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27.2. The Cumulative Statistics System #

   27.2.1. Statistics Collection Configuration
   27.2.2. Viewing Statistics
   27.2.3. pg_stat_activity
   27.2.4. pg_stat_replication
   27.2.5. pg_stat_replication_slots
   27.2.6. pg_stat_wal_receiver
   27.2.7. pg_stat_recovery_prefetch
   27.2.8. pg_stat_subscription
   27.2.9. pg_stat_subscription_stats
   27.2.10. pg_stat_ssl
   27.2.11. pg_stat_gssapi
   27.2.12. pg_stat_archiver
   27.2.13. pg_stat_io
   27.2.14. pg_stat_bgwriter
   27.2.15. pg_stat_checkpointer
   27.2.16. pg_stat_wal
   27.2.17. pg_stat_database
   27.2.18. pg_stat_database_conflicts
   27.2.19. pg_stat_all_tables
   27.2.20. pg_stat_all_indexes
   27.2.21. pg_statio_all_tables
   27.2.22. pg_statio_all_indexes
   27.2.23. pg_statio_all_sequences
   27.2.24. pg_stat_user_functions
   27.2.25. pg_stat_slru
   27.2.26. Statistics Functions

   PostgreSQL's cumulative statistics system supports collection and
   reporting of information about server activity. Presently, accesses to
   tables and indexes in both disk-block and individual-row terms are
   counted. The total number of rows in each table, and information about
   vacuum and analyze actions for each table are also counted. If enabled,
   calls to user-defined functions and the total time spent in each one
   are counted as well.

   PostgreSQL also supports reporting dynamic information about exactly
   what is going on in the system right now, such as the exact command
   currently being executed by other server processes, and which other
   connections exist in the system. This facility is independent of the
   cumulative statistics system.

27.2.1. Statistics Collection Configuration #

   Since collection of statistics adds some overhead to query execution,
   the system can be configured to collect or not collect information.
   This is controlled by configuration parameters that are normally set in
   postgresql.conf. (See Chapter 19 for details about setting
   configuration parameters.)

   The parameter track_activities enables monitoring of the current
   command being executed by any server process.

   The parameter track_cost_delay_timing enables monitoring of cost-based
   vacuum delay.

   The parameter track_counts controls whether cumulative statistics are
   collected about table and index accesses.

   The parameter track_functions enables tracking of usage of user-defined
   functions.

   The parameter track_io_timing enables monitoring of block read, write,
   extend, and fsync times.

   The parameter track_wal_io_timing enables monitoring of WAL read, write
   and fsync times.

   Normally these parameters are set in postgresql.conf so that they apply
   to all server processes, but it is possible to turn them on or off in
   individual sessions using the SET command. (To prevent ordinary users
   from hiding their activity from the administrator, only superusers are
   allowed to change these parameters with SET.)

   Cumulative statistics are collected in shared memory. Every PostgreSQL
   process collects statistics locally, then updates the shared data at
   appropriate intervals. When a server, including a physical replica,
   shuts down cleanly, a permanent copy of the statistics data is stored
   in the pg_stat subdirectory, so that statistics can be retained across
   server restarts. In contrast, when starting from an unclean shutdown
   (e.g., after an immediate shutdown, a server crash, starting from a
   base backup, and point-in-time recovery), all statistics counters are
   reset.

27.2.2. Viewing Statistics #

   Several predefined views, listed in Table 27.1, are available to show
   the current state of the system. There are also several other views,
   listed in Table 27.2, available to show the accumulated statistics.
   Alternatively, one can build custom views using the underlying
   cumulative statistics functions, as discussed in Section 27.2.26.

   When using the cumulative statistics views and functions to monitor
   collected data, it is important to realize that the information does
   not update instantaneously. Each individual server process flushes out
   accumulated statistics to shared memory just before going idle, but not
   more frequently than once per PGSTAT_MIN_INTERVAL milliseconds (1
   second unless altered while building the server); so a query or
   transaction still in progress does not affect the displayed totals and
   the displayed information lags behind actual activity. However,
   current-query information collected by track_activities is always
   up-to-date.

   Another important point is that when a server process is asked to
   display any of the accumulated statistics, accessed values are cached
   until the end of its current transaction in the default configuration.
   So the statistics will show static information as long as you continue
   the current transaction. Similarly, information about the current
   queries of all sessions is collected when any such information is first
   requested within a transaction, and the same information will be
   displayed throughout the transaction. This is a feature, not a bug,
   because it allows you to perform several queries on the statistics and
   correlate the results without worrying that the numbers are changing
   underneath you. When analyzing statistics interactively, or with
   expensive queries, the time delta between accesses to individual
   statistics can lead to significant skew in the cached statistics. To
   minimize skew, stats_fetch_consistency can be set to snapshot, at the
   price of increased memory usage for caching not-needed statistics data.
   Conversely, if it's known that statistics are only accessed once,
   caching accessed statistics is unnecessary and can be avoided by
   setting stats_fetch_consistency to none. You can invoke
   pg_stat_clear_snapshot() to discard the current transaction's
   statistics snapshot or cached values (if any). The next use of
   statistical information will (when in snapshot mode) cause a new
   snapshot to be built or (when in cache mode) accessed statistics to be
   cached.

   A transaction can also see its own statistics (not yet flushed out to
   the shared memory statistics) in the views pg_stat_xact_all_tables,
   pg_stat_xact_sys_tables, pg_stat_xact_user_tables, and
   pg_stat_xact_user_functions. These numbers do not act as stated above;
   instead they update continuously throughout the transaction.

   Some of the information in the dynamic statistics views shown in
   Table 27.1 is security restricted. Ordinary users can only see all the
   information about their own sessions (sessions belonging to a role that
   they are a member of). In rows about other sessions, many columns will
   be null. Note, however, that the existence of a session and its general
   properties such as its sessions user and database are visible to all
   users. Superusers and roles with privileges of built-in role
   pg_read_all_stats can see all the information about all sessions.

   Table 27.1. Dynamic Statistics Views
   View Name Description
   pg_stat_activity One row per server process, showing information
   related to the current activity of that process, such as state and
   current query. See pg_stat_activity for details.
   pg_stat_replication One row per WAL sender process, showing statistics
   about replication to that sender's connected standby server. See
   pg_stat_replication for details.
   pg_stat_wal_receiver Only one row, showing statistics about the WAL
   receiver from that receiver's connected server. See
   pg_stat_wal_receiver for details.
   pg_stat_recovery_prefetch Only one row, showing statistics about blocks
   prefetched during recovery. See pg_stat_recovery_prefetch for details.
   pg_stat_subscription At least one row per subscription, showing
   information about the subscription workers. See pg_stat_subscription
   for details.
   pg_stat_ssl One row per connection (regular and replication), showing
   information about SSL used on this connection. See pg_stat_ssl for
   details.
   pg_stat_gssapi One row per connection (regular and replication),
   showing information about GSSAPI authentication and encryption used on
   this connection. See pg_stat_gssapi for details.
   pg_stat_progress_analyze One row for each backend (including autovacuum
   worker processes) running ANALYZE, showing current progress. See
   Section 27.4.1.
   pg_stat_progress_create_index One row for each backend running CREATE
   INDEX or REINDEX, showing current progress. See Section 27.4.4.
   pg_stat_progress_vacuum One row for each backend (including autovacuum
   worker processes) running VACUUM, showing current progress. See
   Section 27.4.5.
   pg_stat_progress_cluster One row for each backend running CLUSTER or
   VACUUM FULL, showing current progress. See Section 27.4.2.
   pg_stat_progress_basebackup One row for each WAL sender process
   streaming a base backup, showing current progress. See Section 27.4.6.
   pg_stat_progress_copy One row for each backend running COPY, showing
   current progress. See Section 27.4.3.

   Table 27.2. Collected Statistics Views
   View Name Description
   pg_stat_archiver One row only, showing statistics about the WAL
   archiver process's activity. See pg_stat_archiver for details.
   pg_stat_bgwriter One row only, showing statistics about the background
   writer process's activity. See pg_stat_bgwriter for details.
   pg_stat_checkpointer One row only, showing statistics about the
   checkpointer process's activity. See pg_stat_checkpointer for details.
   pg_stat_database One row per database, showing database-wide
   statistics. See pg_stat_database for details.
   pg_stat_database_conflicts One row per database, showing database-wide
   statistics about query cancels due to conflict with recovery on standby
   servers. See pg_stat_database_conflicts for details.
   pg_stat_io One row for each combination of backend type, context, and
   target object containing cluster-wide I/O statistics. See pg_stat_io
   for details.
   pg_stat_replication_slots One row per replication slot, showing
   statistics about the replication slot's usage. See
   pg_stat_replication_slots for details.
   pg_stat_slru One row per SLRU, showing statistics of operations. See
   pg_stat_slru for details.
   pg_stat_subscription_stats One row per subscription, showing statistics
   about errors and conflicts. See pg_stat_subscription_stats for details.
   pg_stat_wal One row only, showing statistics about WAL activity. See
   pg_stat_wal for details.
   pg_stat_all_tables One row for each table in the current database,
   showing statistics about accesses to that specific table. See
   pg_stat_all_tables for details.
   pg_stat_sys_tables Same as pg_stat_all_tables, except that only system
   tables are shown.
   pg_stat_user_tables Same as pg_stat_all_tables, except that only user
   tables are shown.
   pg_stat_xact_all_tables Similar to pg_stat_all_tables, but counts
   actions taken so far within the current transaction (which are not yet
   included in pg_stat_all_tables and related views). The columns for
   numbers of live and dead rows and vacuum and analyze actions are not
   present in this view.
   pg_stat_xact_sys_tables Same as pg_stat_xact_all_tables, except that
   only system tables are shown.
   pg_stat_xact_user_tables Same as pg_stat_xact_all_tables, except that
   only user tables are shown.
   pg_stat_all_indexes One row for each index in the current database,
   showing statistics about accesses to that specific index. See
   pg_stat_all_indexes for details.
   pg_stat_sys_indexes Same as pg_stat_all_indexes, except that only
   indexes on system tables are shown.
   pg_stat_user_indexes Same as pg_stat_all_indexes, except that only
   indexes on user tables are shown.
   pg_stat_user_functions One row for each tracked function, showing
   statistics about executions of that function. See
   pg_stat_user_functions for details.
   pg_stat_xact_user_functions Similar to pg_stat_user_functions, but
   counts only calls during the current transaction (which are not yet
   included in pg_stat_user_functions).
   pg_statio_all_tables One row for each table in the current database,
   showing statistics about I/O on that specific table. See
   pg_statio_all_tables for details.
   pg_statio_sys_tables Same as pg_statio_all_tables, except that only
   system tables are shown.
   pg_statio_user_tables Same as pg_statio_all_tables, except that only
   user tables are shown.
   pg_statio_all_indexes One row for each index in the current database,
   showing statistics about I/O on that specific index. See
   pg_statio_all_indexes for details.
   pg_statio_sys_indexes Same as pg_statio_all_indexes, except that only
   indexes on system tables are shown.
   pg_statio_user_indexes Same as pg_statio_all_indexes, except that only
   indexes on user tables are shown.
   pg_statio_all_sequences One row for each sequence in the current
   database, showing statistics about I/O on that specific sequence. See
   pg_statio_all_sequences for details.
   pg_statio_sys_sequences Same as pg_statio_all_sequences, except that
   only system sequences are shown. (Presently, no system sequences are
   defined, so this view is always empty.)
   pg_statio_user_sequences Same as pg_statio_all_sequences, except that
   only user sequences are shown.

   The per-index statistics are particularly useful to determine which
   indexes are being used and how effective they are.

   The pg_stat_io and pg_statio_ set of views are useful for determining
   the effectiveness of the buffer cache. They can be used to calculate a
   cache hit ratio. Note that while PostgreSQL's I/O statistics capture
   most instances in which the kernel was invoked in order to perform I/O,
   they do not differentiate between data which had to be fetched from
   disk and that which already resided in the kernel page cache. Users are
   advised to use the PostgreSQL statistics views in combination with
   operating system utilities for a more complete picture of their
   database's I/O performance.

27.2.3. pg_stat_activity #

   The pg_stat_activity view will have one row per server process, showing
   information related to the current activity of that process.

   Table 27.3. pg_stat_activity View

   Column Type

   Description

   datid oid

   OID of the database this backend is connected to

   datname name

   Name of the database this backend is connected to

   pid integer

   Process ID of this backend

   leader_pid integer

   Process ID of the parallel group leader if this process is a parallel
   query worker, or process ID of the leader apply worker if this process
   is a parallel apply worker. NULL indicates that this process is a
   parallel group leader or leader apply worker, or does not participate
   in any parallel operation.

   usesysid oid

   OID of the user logged into this backend

   usename name

   Name of the user logged into this backend

   application_name text

   Name of the application that is connected to this backend

   client_addr inet

   IP address of the client connected to this backend. If this field is
   null, it indicates either that the client is connected via a Unix
   socket on the server machine or that this is an internal process such
   as autovacuum.

   client_hostname text

   Host name of the connected client, as reported by a reverse DNS lookup
   of client_addr. This field will only be non-null for IP connections,
   and only when log_hostname is enabled.

   client_port integer

   TCP port number that the client is using for communication with this
   backend, or -1 if a Unix socket is used. If this field is null, it
   indicates that this is an internal server process.

   backend_start timestamp with time zone

   Time when this process was started. For client backends, this is the
   time the client connected to the server.

   xact_start timestamp with time zone

   Time when this process' current transaction was started, or null if no
   transaction is active. If the current query is the first of its
   transaction, this column is equal to the query_start column.

   query_start timestamp with time zone

   Time when the currently active query was started, or if state is not
   active, when the last query was started

   state_change timestamp with time zone

   Time when the state was last changed

   wait_event_type text

   The type of event for which the backend is waiting, if any; otherwise
   NULL. See Table 27.4.

   wait_event text

   Wait event name if backend is currently waiting, otherwise NULL. See
   Table 27.5 through Table 27.13.

   state text

   Current overall state of this backend. Possible values are:
     * starting: The backend is in initial startup. Client authentication
       is performed during this phase.
     * active: The backend is executing a query.
     * idle: The backend is waiting for a new client command.
     * idle in transaction: The backend is in a transaction, but is not
       currently executing a query.
     * idle in transaction (aborted): This state is similar to idle in
       transaction, except one of the statements in the transaction caused
       an error.
     * fastpath function call: The backend is executing a fast-path
       function.
     * disabled: This state is reported if track_activities is disabled in
       this backend.

   backend_xid xid

   Top-level transaction identifier of this backend, if any; see
   Section 67.1.

   backend_xmin xid

   The current backend's xmin horizon.

   query_id bigint

   Identifier of this backend's most recent query. If state is active this
   field shows the identifier of the currently executing query. In all
   other states, it shows the identifier of last query that was executed.
   Query identifiers are not computed by default so this field will be
   null unless compute_query_id parameter is enabled or a third-party
   module that computes query identifiers is configured.

   query text

   Text of this backend's most recent query. If state is active this field
   shows the currently executing query. In all other states, it shows the
   last query that was executed. By default the query text is truncated at
   1024 bytes; this value can be changed via the parameter
   track_activity_query_size.

   backend_type text

   Type of current backend. Possible types are autovacuum launcher,
   autovacuum worker, logical replication launcher, logical replication
   worker, parallel worker, background writer, client backend,
   checkpointer, archiver, standalone backend, startup, walreceiver,
   walsender, walwriter and walsummarizer. In addition, background workers
   registered by extensions may have additional types.

Note

   The wait_event and state columns are independent. If a backend is in
   the active state, it may or may not be waiting on some event. If the
   state is active and wait_event is non-null, it means that a query is
   being executed, but is being blocked somewhere in the system. To keep
   the reporting overhead low, the system does not attempt to synchronize
   different aspects of activity data for a backend. As a result,
   ephemeral discrepancies may exist between the view's columns.

   Table 27.4. Wait Event Types
   Wait Event Type Description
   Activity The server process is idle. This event type indicates a
   process waiting for activity in its main processing loop. wait_event
   will identify the specific wait point; see Table 27.5.
   BufferPin The server process is waiting for exclusive access to a data
   buffer. Buffer pin waits can be protracted if another process holds an
   open cursor that last read data from the buffer in question. See
   Table 27.6.
   Client The server process is waiting for activity on a socket connected
   to a user application. Thus, the server expects something to happen
   that is independent of its internal processes. wait_event will identify
   the specific wait point; see Table 27.7.
   Extension The server process is waiting for some condition defined by
   an extension module. See Table 27.8.
   InjectionPoint The server process is waiting for an injection point to
   reach an outcome defined in a test. See Section 36.10.14 for more
   details. This type has no predefined wait points.
   IO The server process is waiting for an I/O operation to complete.
   wait_event will identify the specific wait point; see Table 27.9.
   IPC The server process is waiting for some interaction with another
   server process. wait_event will identify the specific wait point; see
   Table 27.10.
   Lock The server process is waiting for a heavyweight lock. Heavyweight
   locks, also known as lock manager locks or simply locks, primarily
   protect SQL-visible objects such as tables. However, they are also used
   to ensure mutual exclusion for certain internal operations such as
   relation extension. wait_event will identify the type of lock awaited;
   see Table 27.11.
   LWLock The server process is waiting for a lightweight lock. Most such
   locks protect a particular data structure in shared memory. wait_event
   will contain a name identifying the purpose of the lightweight lock.
   (Some locks have specific names; others are part of a group of locks
   each with a similar purpose.) See Table 27.12.
   Timeout The server process is waiting for a timeout to expire.
   wait_event will identify the specific wait point; see Table 27.13.

   Table 27.5. Wait Events of Type Activity
   Activity Wait Event Description
   ArchiverMain Waiting in main loop of archiver process.
   AutovacuumMain Waiting in main loop of autovacuum launcher process.
   BgwriterHibernate Waiting in background writer process, hibernating.
   BgwriterMain Waiting in main loop of background writer process.
   CheckpointerMain Waiting in main loop of checkpointer process.
   CheckpointerShutdown Waiting for checkpointer process to be terminated.
   IoWorkerMain Waiting in main loop of IO Worker process.
   LogicalApplyMain Waiting in main loop of logical replication apply
   process.
   LogicalLauncherMain Waiting in main loop of logical replication
   launcher process.
   LogicalParallelApplyMain Waiting in main loop of logical replication
   parallel apply process.
   RecoveryWalStream Waiting in main loop of startup process for WAL to
   arrive, during streaming recovery.
   ReplicationSlotsyncMain Waiting in main loop of slot sync worker.
   ReplicationSlotsyncShutdown Waiting for slot sync worker to shut down.
   SysloggerMain Waiting in main loop of syslogger process.
   WalReceiverMain Waiting in main loop of WAL receiver process.
   WalSenderMain Waiting in main loop of WAL sender process.
   WalSummarizerWal Waiting in WAL summarizer for more WAL to be
   generated.
   WalWriterMain Waiting in main loop of WAL writer process.

   Table 27.6. Wait Events of Type Bufferpin
   BufferPin Wait Event                   Description
   BufferPin            Waiting to acquire an exclusive pin on a buffer.

   Table 27.7. Wait Events of Type Client
   Client Wait Event Description
   ClientRead Waiting to read data from the client.
   ClientWrite Waiting to write data to the client.
   GssOpenServer Waiting to read data from the client while establishing a
   GSSAPI session.
   LibpqwalreceiverConnect Waiting in WAL receiver to establish connection
   to remote server.
   LibpqwalreceiverReceive Waiting in WAL receiver to receive data from
   remote server.
   SslOpenServer Waiting for SSL while attempting connection.
   WaitForStandbyConfirmation Waiting for WAL to be received and flushed
   by the physical standby.
   WalSenderWaitForWal Waiting for WAL to be flushed in WAL sender
   process.
   WalSenderWriteData Waiting for any activity when processing replies
   from WAL receiver in WAL sender process.

   Table 27.8. Wait Events of Type Extension
   Extension Wait Event       Description
   Extension            Waiting in an extension.

   Table 27.9. Wait Events of Type Io
   IO Wait Event Description
   AioIoCompletion Waiting for another process to complete IO.
   AioIoUringExecution Waiting for IO execution via io_uring.
   AioIoUringSubmit Waiting for IO submission via io_uring.
   BasebackupRead Waiting for base backup to read from a file.
   BasebackupSync Waiting for data written by a base backup to reach
   durable storage.
   BasebackupWrite Waiting for base backup to write to a file.
   BuffileRead Waiting for a read from a buffered file.
   BuffileTruncate Waiting for a buffered file to be truncated.
   BuffileWrite Waiting for a write to a buffered file.
   ControlFileRead Waiting for a read from the pg_control file.
   ControlFileSync Waiting for the pg_control file to reach durable
   storage.
   ControlFileSyncUpdate Waiting for an update to the pg_control file to
   reach durable storage.
   ControlFileWrite Waiting for a write to the pg_control file.
   ControlFileWriteUpdate Waiting for a write to update the pg_control
   file.
   CopyFileCopy Waiting for a file copy operation.
   CopyFileRead Waiting for a read during a file copy operation.
   CopyFileWrite Waiting for a write during a file copy operation.
   DataFileExtend Waiting for a relation data file to be extended.
   DataFileFlush Waiting for a relation data file to reach durable
   storage.
   DataFileImmediateSync Waiting for an immediate synchronization of a
   relation data file to durable storage.
   DataFilePrefetch Waiting for an asynchronous prefetch from a relation
   data file.
   DataFileRead Waiting for a read from a relation data file.
   DataFileSync Waiting for changes to a relation data file to reach
   durable storage.
   DataFileTruncate Waiting for a relation data file to be truncated.
   DataFileWrite Waiting for a write to a relation data file.
   DsmAllocate Waiting for a dynamic shared memory segment to be
   allocated.
   DsmFillZeroWrite Waiting to fill a dynamic shared memory backing file
   with zeroes.
   LockFileAddtodatadirRead Waiting for a read while adding a line to the
   data directory lock file.
   LockFileAddtodatadirSync Waiting for data to reach durable storage
   while adding a line to the data directory lock file.
   LockFileAddtodatadirWrite Waiting for a write while adding a line to
   the data directory lock file.
   LockFileCreateRead Waiting to read while creating the data directory
   lock file.
   LockFileCreateSync Waiting for data to reach durable storage while
   creating the data directory lock file.
   LockFileCreateWrite Waiting for a write while creating the data
   directory lock file.
   LockFileRecheckdatadirRead Waiting for a read during recheck of the
   data directory lock file.
   LogicalRewriteCheckpointSync Waiting for logical rewrite mappings to
   reach durable storage during a checkpoint.
   LogicalRewriteMappingSync Waiting for mapping data to reach durable
   storage during a logical rewrite.
   LogicalRewriteMappingWrite Waiting for a write of mapping data during a
   logical rewrite.
   LogicalRewriteSync Waiting for logical rewrite mappings to reach
   durable storage.
   LogicalRewriteTruncate Waiting for truncate of mapping data during a
   logical rewrite.
   LogicalRewriteWrite Waiting for a write of logical rewrite mappings.
   RelationMapRead Waiting for a read of the relation map file.
   RelationMapReplace Waiting for durable replacement of a relation map
   file.
   RelationMapWrite Waiting for a write to the relation map file.
   ReorderBufferRead Waiting for a read during reorder buffer management.
   ReorderBufferWrite Waiting for a write during reorder buffer
   management.
   ReorderLogicalMappingRead Waiting for a read of a logical mapping
   during reorder buffer management.
   ReplicationSlotRead Waiting for a read from a replication slot control
   file.
   ReplicationSlotRestoreSync Waiting for a replication slot control file
   to reach durable storage while restoring it to memory.
   ReplicationSlotSync Waiting for a replication slot control file to
   reach durable storage.
   ReplicationSlotWrite Waiting for a write to a replication slot control
   file.
   SlruFlushSync Waiting for SLRU data to reach durable storage during a
   checkpoint or database shutdown.
   SlruRead Waiting for a read of an SLRU page.
   SlruSync Waiting for SLRU data to reach durable storage following a
   page write.
   SlruWrite Waiting for a write of an SLRU page.
   SnapbuildRead Waiting for a read of a serialized historical catalog
   snapshot.
   SnapbuildSync Waiting for a serialized historical catalog snapshot to
   reach durable storage.
   SnapbuildWrite Waiting for a write of a serialized historical catalog
   snapshot.
   TimelineHistoryFileSync Waiting for a timeline history file received
   via streaming replication to reach durable storage.
   TimelineHistoryFileWrite Waiting for a write of a timeline history file
   received via streaming replication.
   TimelineHistoryRead Waiting for a read of a timeline history file.
   TimelineHistorySync Waiting for a newly created timeline history file
   to reach durable storage.
   TimelineHistoryWrite Waiting for a write of a newly created timeline
   history file.
   TwophaseFileRead Waiting for a read of a two phase state file.
   TwophaseFileSync Waiting for a two phase state file to reach durable
   storage.
   TwophaseFileWrite Waiting for a write of a two phase state file.
   VersionFileSync Waiting for the version file to reach durable storage
   while creating a database.
   VersionFileWrite Waiting for the version file to be written while
   creating a database.
   WalsenderTimelineHistoryRead Waiting for a read from a timeline history
   file during a walsender timeline command.
   WalBootstrapSync Waiting for WAL to reach durable storage during
   bootstrapping.
   WalBootstrapWrite Waiting for a write of a WAL page during
   bootstrapping.
   WalCopyRead Waiting for a read when creating a new WAL segment by
   copying an existing one.
   WalCopySync Waiting for a new WAL segment created by copying an
   existing one to reach durable storage.
   WalCopyWrite Waiting for a write when creating a new WAL segment by
   copying an existing one.
   WalInitSync Waiting for a newly initialized WAL file to reach durable
   storage.
   WalInitWrite Waiting for a write while initializing a new WAL file.
   WalRead Waiting for a read from a WAL file.
   WalSummaryRead Waiting for a read from a WAL summary file.
   WalSummaryWrite Waiting for a write to a WAL summary file.
   WalSync Waiting for a WAL file to reach durable storage.
   WalSyncMethodAssign Waiting for data to reach durable storage while
   assigning a new WAL sync method.
   WalWrite Waiting for a write to a WAL file.

   Table 27.10. Wait Events of Type Ipc
   IPC Wait Event Description
   AppendReady Waiting for subplan nodes of an Append plan node to be
   ready.
   ArchiveCleanupCommand Waiting for archive_cleanup_command to complete.
   ArchiveCommand Waiting for archive_command to complete.
   BackendTermination Waiting for the termination of another backend.
   BackupWaitWalArchive Waiting for WAL files required for a backup to be
   successfully archived.
   BgworkerShutdown Waiting for background worker to shut down.
   BgworkerStartup Waiting for background worker to start up.
   BtreePage Waiting for the page number needed to continue a parallel
   B-tree scan to become available.
   BufferIo Waiting for buffer I/O to complete.
   CheckpointDelayComplete Waiting for a backend that blocks a checkpoint
   from completing.
   CheckpointDelayStart Waiting for a backend that blocks a checkpoint
   from starting.
   CheckpointDone Waiting for a checkpoint to complete.
   CheckpointStart Waiting for a checkpoint to start.
   ExecuteGather Waiting for activity from a child process while executing
   a Gather plan node.
   HashBatchAllocate Waiting for an elected Parallel Hash participant to
   allocate a hash table.
   HashBatchElect Waiting to elect a Parallel Hash participant to allocate
   a hash table.
   HashBatchLoad Waiting for other Parallel Hash participants to finish
   loading a hash table.
   HashBuildAllocate Waiting for an elected Parallel Hash participant to
   allocate the initial hash table.
   HashBuildElect Waiting to elect a Parallel Hash participant to allocate
   the initial hash table.
   HashBuildHashInner Waiting for other Parallel Hash participants to
   finish hashing the inner relation.
   HashBuildHashOuter Waiting for other Parallel Hash participants to
   finish partitioning the outer relation.
   HashGrowBatchesDecide Waiting to elect a Parallel Hash participant to
   decide on future batch growth.
   HashGrowBatchesElect Waiting to elect a Parallel Hash participant to
   allocate more batches.
   HashGrowBatchesFinish Waiting for an elected Parallel Hash participant
   to decide on future batch growth.
   HashGrowBatchesReallocate Waiting for an elected Parallel Hash
   participant to allocate more batches.
   HashGrowBatchesRepartition Waiting for other Parallel Hash participants
   to finish repartitioning.
   HashGrowBucketsElect Waiting to elect a Parallel Hash participant to
   allocate more buckets.
   HashGrowBucketsReallocate Waiting for an elected Parallel Hash
   participant to finish allocating more buckets.
   HashGrowBucketsReinsert Waiting for other Parallel Hash participants to
   finish inserting tuples into new buckets.
   LogicalApplySendData Waiting for a logical replication leader apply
   process to send data to a parallel apply process.
   LogicalParallelApplyStateChange Waiting for a logical replication
   parallel apply process to change state.
   LogicalSyncData Waiting for a logical replication remote server to send
   data for initial table synchronization.
   LogicalSyncStateChange Waiting for a logical replication remote server
   to change state.
   MessageQueueInternal Waiting for another process to be attached to a
   shared message queue.
   MessageQueuePutMessage Waiting to write a protocol message to a shared
   message queue.
   MessageQueueReceive Waiting to receive bytes from a shared message
   queue.
   MessageQueueSend Waiting to send bytes to a shared message queue.
   MultixactCreation Waiting for a multixact creation to complete.
   ParallelBitmapScan Waiting for parallel bitmap scan to become
   initialized.
   ParallelCreateIndexScan Waiting for parallel CREATE INDEX workers to
   finish heap scan.
   ParallelFinish Waiting for parallel workers to finish computing.
   ProcarrayGroupUpdate Waiting for the group leader to clear the
   transaction ID at transaction end.
   ProcSignalBarrier Waiting for a barrier event to be processed by all
   backends.
   Promote Waiting for standby promotion.
   RecoveryConflictSnapshot Waiting for recovery conflict resolution for a
   vacuum cleanup.
   RecoveryConflictTablespace Waiting for recovery conflict resolution for
   dropping a tablespace.
   RecoveryEndCommand Waiting for recovery_end_command to complete.
   RecoveryPause Waiting for recovery to be resumed.
   ReplicationOriginDrop Waiting for a replication origin to become
   inactive so it can be dropped.
   ReplicationSlotDrop Waiting for a replication slot to become inactive
   so it can be dropped.
   RestoreCommand Waiting for restore_command to complete.
   SafeSnapshot Waiting to obtain a valid snapshot for a READ ONLY
   DEFERRABLE transaction.
   SyncRep Waiting for confirmation from a remote server during
   synchronous replication.
   WalReceiverExit Waiting for the WAL receiver to exit.
   WalReceiverWaitStart Waiting for startup process to send initial data
   for streaming replication.
   WalSummaryReady Waiting for a new WAL summary to be generated.
   XactGroupUpdate Waiting for the group leader to update transaction
   status at transaction end.

   Table 27.11. Wait Events of Type Lock
   Lock Wait Event Description
   advisory Waiting to acquire an advisory user lock.
   applytransaction Waiting to acquire a lock on a remote transaction
   being applied by a logical replication subscriber.
   extend Waiting to extend a relation.
   frozenid Waiting to update pg_database.datfrozenxid and
   pg_database.datminmxid.
   object Waiting to acquire a lock on a non-relation database object.
   page Waiting to acquire a lock on a page of a relation.
   relation Waiting to acquire a lock on a relation.
   spectoken Waiting to acquire a speculative insertion lock.
   transactionid Waiting for a transaction to finish.
   tuple Waiting to acquire a lock on a tuple.
   userlock Waiting to acquire a user lock.
   virtualxid Waiting to acquire a virtual transaction ID lock; see
   Section 67.1.

   Table 27.12. Wait Events of Type Lwlock
   LWLock Wait Event Description
   AddinShmemInit Waiting to manage an extension's space allocation in
   shared memory.
   AioUringCompletion Waiting for another process to complete IO via
   io_uring.
   AioWorkerSubmissionQueue Waiting to access AIO worker submission queue.
   AutoFile Waiting to update the postgresql.auto.conf file.
   Autovacuum Waiting to read or update the current state of autovacuum
   workers.
   AutovacuumSchedule Waiting to ensure that a table selected for
   autovacuum still needs vacuuming.
   BackgroundWorker Waiting to read or update background worker state.
   BtreeVacuum Waiting to read or update vacuum-related information for a
   B-tree index.
   BufferContent Waiting to access a data page in memory.
   BufferMapping Waiting to associate a data block with a buffer in the
   buffer pool.
   CheckpointerComm Waiting to manage fsync requests.
   CommitTs Waiting to read or update the last value set for a transaction
   commit timestamp.
   CommitTsBuffer Waiting for I/O on a commit timestamp SLRU buffer.
   CommitTsSLRU Waiting to access the commit timestamp SLRU cache.
   ControlFile Waiting to read or update the pg_control file or create a
   new WAL file.
   DSMRegistry Waiting to read or update the dynamic shared memory
   registry.
   DSMRegistryDSA Waiting to access dynamic shared memory registry's
   dynamic shared memory allocator.
   DSMRegistryHash Waiting to access dynamic shared memory registry's
   shared hash table.
   DynamicSharedMemoryControl Waiting to read or update dynamic shared
   memory allocation information.
   InjectionPoint Waiting to read or update information related to
   injection points.
   LockFastPath Waiting to read or update a process' fast-path lock
   information.
   LockManager Waiting to read or update information about “heavyweight”
   locks.
   LogicalRepLauncherDSA Waiting to access logical replication launcher's
   dynamic shared memory allocator.
   LogicalRepLauncherHash Waiting to access logical replication launcher's
   shared hash table.
   LogicalRepWorker Waiting to read or update the state of logical
   replication workers.
   MultiXactGen Waiting to read or update shared multixact state.
   MultiXactMemberBuffer Waiting for I/O on a multixact member SLRU
   buffer.
   MultiXactMemberSLRU Waiting to access the multixact member SLRU cache.
   MultiXactOffsetBuffer Waiting for I/O on a multixact offset SLRU
   buffer.
   MultiXactOffsetSLRU Waiting to access the multixact offset SLRU cache.
   MultiXactTruncation Waiting to read or truncate multixact information.
   NotifyBuffer Waiting for I/O on a NOTIFY message SLRU buffer.
   NotifyQueue Waiting to read or update NOTIFY messages.
   NotifyQueueTail Waiting to update limit on NOTIFY message storage.
   NotifySLRU Waiting to access the NOTIFY message SLRU cache.
   OidGen Waiting to allocate a new OID.
   ParallelAppend Waiting to choose the next subplan during Parallel
   Append plan execution.
   ParallelBtreeScan Waiting to synchronize workers during Parallel B-tree
   scan plan execution.
   ParallelHashJoin Waiting to synchronize workers during Parallel Hash
   Join plan execution.
   ParallelQueryDSA Waiting for parallel query dynamic shared memory
   allocation.
   ParallelVacuumDSA Waiting for parallel vacuum dynamic shared memory
   allocation.
   PerSessionDSA Waiting for parallel query dynamic shared memory
   allocation.
   PerSessionRecordType Waiting to access a parallel query's information
   about composite types.
   PerSessionRecordTypmod Waiting to access a parallel query's information
   about type modifiers that identify anonymous record types.
   PerXactPredicateList Waiting to access the list of predicate locks held
   by the current serializable transaction during a parallel query.
   PgStatsData Waiting for shared memory stats data access.
   PgStatsDSA Waiting for stats dynamic shared memory allocator access.
   PgStatsHash Waiting for stats shared memory hash table access.
   PredicateLockManager Waiting to access predicate lock information used
   by serializable transactions.
   ProcArray Waiting to access the shared per-process data structures
   (typically, to get a snapshot or report a session's transaction ID).
   RelationMapping Waiting to read or update a pg_filenode.map file (used
   to track the filenode assignments of certain system catalogs).
   RelCacheInit Waiting to read or update a pg_internal.init relation
   cache initialization file.
   ReplicationOrigin Waiting to create, drop or use a replication origin.
   ReplicationOriginState Waiting to read or update the progress of one
   replication origin.
   ReplicationSlotAllocation Waiting to allocate or free a replication
   slot.
   ReplicationSlotControl Waiting to read or update replication slot
   state.
   ReplicationSlotIO Waiting for I/O on a replication slot.
   SerialBuffer Waiting for I/O on a serializable transaction conflict
   SLRU buffer.
   SerialControl Waiting to read or update shared pg_serial state.
   SerializableFinishedList Waiting to access the list of finished
   serializable transactions.
   SerializablePredicateList Waiting to access the list of predicate locks
   held by serializable transactions.
   SerializableXactHash Waiting to read or update information about
   serializable transactions.
   SerialSLRU Waiting to access the serializable transaction conflict SLRU
   cache.
   SharedTidBitmap Waiting to access a shared TID bitmap during a parallel
   bitmap index scan.
   SharedTupleStore Waiting to access a shared tuple store during parallel
   query.
   ShmemIndex Waiting to find or allocate space in shared memory.
   SInvalRead Waiting to retrieve messages from the shared catalog
   invalidation queue.
   SInvalWrite Waiting to add a message to the shared catalog invalidation
   queue.
   SubtransBuffer Waiting for I/O on a sub-transaction SLRU buffer.
   SubtransSLRU Waiting to access the sub-transaction SLRU cache.
   SyncRep Waiting to read or update information about the state of
   synchronous replication.
   SyncScan Waiting to select the starting location of a synchronized
   table scan.
   TablespaceCreate Waiting to create or drop a tablespace.
   TwoPhaseState Waiting to read or update the state of prepared
   transactions.
   WaitEventCustom Waiting to read or update custom wait events
   information.
   WALBufMapping Waiting to replace a page in WAL buffers.
   WALInsert Waiting to insert WAL data into a memory buffer.
   WALSummarizer Waiting to read or update WAL summarization state.
   WALWrite Waiting for WAL buffers to be written to disk.
   WrapLimitsVacuum Waiting to update limits on transaction id and
   multixact consumption.
   XactBuffer Waiting for I/O on a transaction status SLRU buffer.
   XactSLRU Waiting to access the transaction status SLRU cache.
   XactTruncation Waiting to execute pg_xact_status or update the oldest
   transaction ID available to it.
   XidGen Waiting to allocate a new transaction ID.

   Table 27.13. Wait Events of Type Timeout
   Timeout Wait Event Description
   BaseBackupThrottle Waiting during base backup when throttling activity.
   CheckpointWriteDelay Waiting between writes while performing a
   checkpoint.
   PgSleep Waiting due to a call to pg_sleep or a sibling function.
   RecoveryApplyDelay Waiting to apply WAL during recovery because of a
   delay setting.
   RecoveryRetrieveRetryInterval Waiting during recovery when WAL data is
   not available from any source (pg_wal, archive or stream).
   RegisterSyncRequest Waiting while sending synchronization requests to
   the checkpointer, because the request queue is full.
   SpinDelay Waiting while acquiring a contended spinlock.
   VacuumDelay Waiting in a cost-based vacuum delay point.
   VacuumTruncate Waiting to acquire an exclusive lock to truncate off any
   empty pages at the end of a table vacuumed.
   WalSummarizerError Waiting after a WAL summarizer error.

   Here are examples of how wait events can be viewed:
SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
s NOT NULL;
 pid  | wait_event_type | wait_event
------+-----------------+------------
 2540 | Lock            | relation
 6644 | LWLock          | ProcArray
(2 rows)

SELECT a.pid, a.wait_event, w.description
  FROM pg_stat_activity a JOIN
       pg_wait_events w ON (a.wait_event_type = w.type AND
                            a.wait_event = w.name)
  WHERE a.wait_event is NOT NULL and a.state = 'active';
-[ RECORD 1 ]------------------------------------------------------​------------
pid         | 686674
wait_event  | WALInitSync
description | Waiting for a newly initialized WAL file to reach durable storage

Note

   Extensions can add Extension, InjectionPoint, and LWLock events to the
   lists shown in Table 27.8 and Table 27.12. In some cases, the name of
   an LWLock assigned by an extension will not be available in all server
   processes. It might be reported as just “extension” rather than the
   extension-assigned name.

27.2.4. pg_stat_replication #

   The pg_stat_replication view will contain one row per WAL sender
   process, showing statistics about replication to that sender's
   connected standby server. Only directly connected standbys are listed;
   no information is available about downstream standby servers.

   Table 27.14. pg_stat_replication View

   Column Type

   Description

   pid integer

   Process ID of a WAL sender process

   usesysid oid

   OID of the user logged into this WAL sender process

   usename name

   Name of the user logged into this WAL sender process

   application_name text

   Name of the application that is connected to this WAL sender

   client_addr inet

   IP address of the client connected to this WAL sender. If this field is
   null, it indicates that the client is connected via a Unix socket on
   the server machine.

   client_hostname text

   Host name of the connected client, as reported by a reverse DNS lookup
   of client_addr. This field will only be non-null for IP connections,
   and only when log_hostname is enabled.

   client_port integer

   TCP port number that the client is using for communication with this
   WAL sender, or -1 if a Unix socket is used

   backend_start timestamp with time zone

   Time when this process was started, i.e., when the client connected to
   this WAL sender

   backend_xmin xid

   This standby's xmin horizon reported by hot_standby_feedback.

   state text

   Current WAL sender state. Possible values are:
     * startup: This WAL sender is starting up.
     * catchup: This WAL sender's connected standby is catching up with
       the primary.
     * streaming: This WAL sender is streaming changes after its connected
       standby server has caught up with the primary.
     * backup: This WAL sender is sending a backup.
     * stopping: This WAL sender is stopping.

   sent_lsn pg_lsn

   Last write-ahead log location sent on this connection

   write_lsn pg_lsn

   Last write-ahead log location written to disk by this standby server

   flush_lsn pg_lsn

   Last write-ahead log location flushed to disk by this standby server

   replay_lsn pg_lsn

   Last write-ahead log location replayed into the database on this
   standby server

   write_lag interval

   Time elapsed between flushing recent WAL locally and receiving
   notification that this standby server has written it (but not yet
   flushed it or applied it). This can be used to gauge the delay that
   synchronous_commit level remote_write incurred while committing if this
   server was configured as a synchronous standby.

   flush_lag interval

   Time elapsed between flushing recent WAL locally and receiving
   notification that this standby server has written and flushed it (but
   not yet applied it). This can be used to gauge the delay that
   synchronous_commit level on incurred while committing if this server
   was configured as a synchronous standby.

   replay_lag interval

   Time elapsed between flushing recent WAL locally and receiving
   notification that this standby server has written, flushed and applied
   it. This can be used to gauge the delay that synchronous_commit level
   remote_apply incurred while committing if this server was configured as
   a synchronous standby.

   sync_priority integer

   Priority of this standby server for being chosen as the synchronous
   standby in a priority-based synchronous replication. This has no effect
   in a quorum-based synchronous replication.

   sync_state text

   Synchronous state of this standby server. Possible values are:
     * async: This standby server is asynchronous.
     * potential: This standby server is now asynchronous, but can
       potentially become synchronous if one of current synchronous ones
       fails.
     * sync: This standby server is synchronous.
     * quorum: This standby server is considered as a candidate for quorum
       standbys.

   reply_time timestamp with time zone

   Send time of last reply message received from standby server

   The lag times reported in the pg_stat_replication view are measurements
   of the time taken for recent WAL to be written, flushed and replayed
   and for the sender to know about it. These times represent the commit
   delay that was (or would have been) introduced by each synchronous
   commit level, if the remote server was configured as a synchronous
   standby. For an asynchronous standby, the replay_lag column
   approximates the delay before recent transactions became visible to
   queries. If the standby server has entirely caught up with the sending
   server and there is no more WAL activity, the most recently measured
   lag times will continue to be displayed for a short time and then show
   NULL.

   Lag times work automatically for physical replication. Logical decoding
   plugins may optionally emit tracking messages; if they do not, the
   tracking mechanism will simply display NULL lag.

Note

   The reported lag times are not predictions of how long it will take for
   the standby to catch up with the sending server assuming the current
   rate of replay. Such a system would show similar times while new WAL is
   being generated, but would differ when the sender becomes idle. In
   particular, when the standby has caught up completely,
   pg_stat_replication shows the time taken to write, flush and replay the
   most recent reported WAL location rather than zero as some users might
   expect. This is consistent with the goal of measuring synchronous
   commit and transaction visibility delays for recent write transactions.
   To reduce confusion for users expecting a different model of lag, the
   lag columns revert to NULL after a short time on a fully replayed idle
   system. Monitoring systems should choose whether to represent this as
   missing data, zero or continue to display the last known value.

27.2.5. pg_stat_replication_slots #

   The pg_stat_replication_slots view will contain one row per logical
   replication slot, showing statistics about its usage.

   Table 27.15. pg_stat_replication_slots View

   Column Type

   Description

   slot_name text

   A unique, cluster-wide identifier for the replication slot

   spill_txns bigint

   Number of transactions spilled to disk once the memory used by logical
   decoding to decode changes from WAL has exceeded
   logical_decoding_work_mem. The counter gets incremented for both
   top-level transactions and subtransactions.

   spill_count bigint

   Number of times transactions were spilled to disk while decoding
   changes from WAL for this slot. This counter is incremented each time a
   transaction is spilled, and the same transaction may be spilled
   multiple times.

   spill_bytes bigint

   Amount of decoded transaction data spilled to disk while performing
   decoding of changes from WAL for this slot. This and other spill
   counters can be used to gauge the I/O which occurred during logical
   decoding and allow tuning logical_decoding_work_mem.

   stream_txns bigint

   Number of in-progress transactions streamed to the decoding output
   plugin after the memory used by logical decoding to decode changes from
   WAL for this slot has exceeded logical_decoding_work_mem. Streaming
   only works with top-level transactions (subtransactions can't be
   streamed independently), so the counter is not incremented for
   subtransactions.

   stream_countbigint

   Number of times in-progress transactions were streamed to the decoding
   output plugin while decoding changes from WAL for this slot. This
   counter is incremented each time a transaction is streamed, and the
   same transaction may be streamed multiple times.

   stream_bytesbigint

   Amount of transaction data decoded for streaming in-progress
   transactions to the decoding output plugin while decoding changes from
   WAL for this slot. This and other streaming counters for this slot can
   be used to tune logical_decoding_work_mem.

   total_txns bigint

   Number of decoded transactions sent to the decoding output plugin for
   this slot. This counts top-level transactions only, and is not
   incremented for subtransactions. Note that this includes the
   transactions that are streamed and/or spilled.

   total_bytesbigint

   Amount of transaction data decoded for sending transactions to the
   decoding output plugin while decoding changes from WAL for this slot.
   Note that this includes data that is streamed and/or spilled.

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

27.2.6. pg_stat_wal_receiver #

   The pg_stat_wal_receiver view will contain only one row, showing
   statistics about the WAL receiver from that receiver's connected
   server.

   Table 27.16. pg_stat_wal_receiver View

   Column Type

   Description

   pid integer

   Process ID of the WAL receiver process

   status text

   Activity status of the WAL receiver process

   receive_start_lsn pg_lsn

   First write-ahead log location used when WAL receiver is started

   receive_start_tli integer

   First timeline number used when WAL receiver is started

   written_lsn pg_lsn

   Last write-ahead log location already received and written to disk, but
   not flushed. This should not be used for data integrity checks.

   flushed_lsn pg_lsn

   Last write-ahead log location already received and flushed to disk, the
   initial value of this field being the first log location used when WAL
   receiver is started

   received_tli integer

   Timeline number of last write-ahead log location received and flushed
   to disk, the initial value of this field being the timeline number of
   the first log location used when WAL receiver is started

   last_msg_send_time timestamp with time zone

   Send time of last message received from origin WAL sender

   last_msg_receipt_time timestamp with time zone

   Receipt time of last message received from origin WAL sender

   latest_end_lsn pg_lsn

   Last write-ahead log location reported to origin WAL sender

   latest_end_time timestamp with time zone

   Time of last write-ahead log location reported to origin WAL sender

   slot_name text

   Replication slot name used by this WAL receiver

   sender_host text

   Host of the PostgreSQL instance this WAL receiver is connected to. This
   can be a host name, an IP address, or a directory path if the
   connection is via Unix socket. (The path case can be distinguished
   because it will always be an absolute path, beginning with /.)

   sender_port integer

   Port number of the PostgreSQL instance this WAL receiver is connected
   to.

   conninfo text

   Connection string used by this WAL receiver, with security-sensitive
   fields obfuscated.

27.2.7. pg_stat_recovery_prefetch #

   The pg_stat_recovery_prefetch view will contain only one row. The
   columns wal_distance, block_distance and io_depth show current values,
   and the other columns show cumulative counters that can be reset with
   the pg_stat_reset_shared function.

   Table 27.17. pg_stat_recovery_prefetch View

   Column Type

   Description

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

   prefetch bigint

   Number of blocks prefetched because they were not in the buffer pool

   hit bigint

   Number of blocks not prefetched because they were already in the buffer
   pool

   skip_init bigint

   Number of blocks not prefetched because they would be zero-initialized

   skip_new bigint

   Number of blocks not prefetched because they didn't exist yet

   skip_fpw bigint

   Number of blocks not prefetched because a full page image was included
   in the WAL

   skip_rep bigint

   Number of blocks not prefetched because they were already recently
   prefetched

   wal_distance int

   How many bytes ahead the prefetcher is looking

   block_distance int

   How many blocks ahead the prefetcher is looking

   io_depth int

   How many prefetches have been initiated but are not yet known to have
   completed

27.2.8. pg_stat_subscription #

   Table 27.18. pg_stat_subscription View

   Column Type

   Description

   subid oid

   OID of the subscription

   subname name

   Name of the subscription

   worker_type text

   Type of the subscription worker process. Possible types are apply,
   parallel apply, and table synchronization.

   pid integer

   Process ID of the subscription worker process

   leader_pid integer

   Process ID of the leader apply worker if this process is a parallel
   apply worker; NULL if this process is a leader apply worker or a table
   synchronization worker

   relid oid

   OID of the relation that the worker is synchronizing; NULL for the
   leader apply worker and parallel apply workers

   received_lsn pg_lsn

   Last write-ahead log location received, the initial value of this field
   being 0; NULL for parallel apply workers

   last_msg_send_time timestamp with time zone

   Send time of last message received from origin WAL sender; NULL for
   parallel apply workers

   last_msg_receipt_time timestamp with time zone

   Receipt time of last message received from origin WAL sender; NULL for
   parallel apply workers

   latest_end_lsn pg_lsn

   Last write-ahead log location reported to origin WAL sender; NULL for
   parallel apply workers

   latest_end_time timestamp with time zone

   Time of last write-ahead log location reported to origin WAL sender;
   NULL for parallel apply workers

27.2.9. pg_stat_subscription_stats #

   The pg_stat_subscription_stats view will contain one row per
   subscription.

   Table 27.19. pg_stat_subscription_stats View

   Column Type

   Description

   subid oid

   OID of the subscription

   subname name

   Name of the subscription

   apply_error_count bigint

   Number of times an error occurred while applying changes. Note that any
   conflict resulting in an apply error will be counted in both
   apply_error_count and the corresponding conflict count (e.g., confl_*).

   sync_error_count bigint

   Number of times an error occurred during the initial table
   synchronization

   confl_insert_exists bigint

   Number of times a row insertion violated a NOT DEFERRABLE unique
   constraint during the application of changes. See insert_exists for
   details about this conflict.

   confl_update_origin_differs bigint

   Number of times an update was applied to a row that had been previously
   modified by another source during the application of changes. See
   update_origin_differs for details about this conflict.

   confl_update_exists bigint

   Number of times that an updated row value violated a NOT DEFERRABLE
   unique constraint during the application of changes. See update_exists
   for details about this conflict.

   confl_update_missing bigint

   Number of times the tuple to be updated was not found during the
   application of changes. See update_missing for details about this
   conflict.

   confl_delete_origin_differs bigint

   Number of times a delete operation was applied to row that had been
   previously modified by another source during the application of
   changes. See delete_origin_differs for details about this conflict.

   confl_delete_missing bigint

   Number of times the tuple to be deleted was not found during the
   application of changes. See delete_missing for details about this
   conflict.

   confl_multiple_unique_conflicts bigint

   Number of times a row insertion or an updated row values violated
   multiple NOT DEFERRABLE unique constraints during the application of
   changes. See multiple_unique_conflicts for details about this conflict.

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

27.2.10. pg_stat_ssl #

   The pg_stat_ssl view will contain one row per backend or WAL sender
   process, showing statistics about SSL usage on this connection. It can
   be joined to pg_stat_activity or pg_stat_replication on the pid column
   to get more details about the connection.

   Table 27.20. pg_stat_ssl View

   Column Type

   Description

   pid integer

   Process ID of a backend or WAL sender process

   ssl boolean

   True if SSL is used on this connection

   version text

   Version of SSL in use, or NULL if SSL is not in use on this connection

   cipher text

   Name of SSL cipher in use, or NULL if SSL is not in use on this
   connection

   bits integer

   Number of bits in the encryption algorithm used, or NULL if SSL is not
   used on this connection

   client_dn text

   Distinguished Name (DN) field from the client certificate used, or NULL
   if no client certificate was supplied or if SSL is not in use on this
   connection. This field is truncated if the DN field is longer than
   NAMEDATALEN (64 characters in a standard build).

   client_serial numeric

   Serial number of the client certificate, or NULL if no client
   certificate was supplied or if SSL is not in use on this connection.
   The combination of certificate serial number and certificate issuer
   uniquely identifies a certificate (unless the issuer erroneously reuses
   serial numbers).

   issuer_dn text

   DN of the issuer of the client certificate, or NULL if no client
   certificate was supplied or if SSL is not in use on this connection.
   This field is truncated like client_dn.

27.2.11. pg_stat_gssapi #

   The pg_stat_gssapi view will contain one row per backend, showing
   information about GSSAPI usage on this connection. It can be joined to
   pg_stat_activity or pg_stat_replication on the pid column to get more
   details about the connection.

   Table 27.21. pg_stat_gssapi View

   Column Type

   Description

   pid integer

   Process ID of a backend

   gss_authenticated boolean

   True if GSSAPI authentication was used for this connection

   principal text

   Principal used to authenticate this connection, or NULL if GSSAPI was
   not used to authenticate this connection. This field is truncated if
   the principal is longer than NAMEDATALEN (64 characters in a standard
   build).

   encrypted boolean

   True if GSSAPI encryption is in use on this connection

   credentials_delegated boolean

   True if GSSAPI credentials were delegated on this connection.

27.2.12. pg_stat_archiver #

   The pg_stat_archiver view will always have a single row, containing
   data about the archiver process of the cluster.

   Table 27.22. pg_stat_archiver View

   Column Type

   Description

   archived_count bigint

   Number of WAL files that have been successfully archived

   last_archived_wal text

   Name of the WAL file most recently successfully archived

   last_archived_time timestamp with time zone

   Time of the most recent successful archive operation

   failed_count bigint

   Number of failed attempts for archiving WAL files

   last_failed_wal text

   Name of the WAL file of the most recent failed archival operation

   last_failed_time timestamp with time zone

   Time of the most recent failed archival operation

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

   Normally, WAL files are archived in order, oldest to newest, but that
   is not guaranteed, and does not hold under special circumstances like
   when promoting a standby or after crash recovery. Therefore it is not
   safe to assume that all files older than last_archived_wal have also
   been successfully archived.

27.2.13. pg_stat_io #

   The pg_stat_io view will contain one row for each combination of
   backend type, target I/O object, and I/O context, showing cluster-wide
   I/O statistics. Combinations which do not make sense are omitted.

   Currently, I/O on relations (e.g. tables, indexes) and WAL activity are
   tracked. However, relation I/O which bypasses shared buffers (e.g. when
   moving a table from one tablespace to another) is currently not
   tracked.

   Table 27.23. pg_stat_io View

   Column Type

   Description

   backend_type text

   Type of backend (e.g. background worker, autovacuum worker). See
   pg_stat_activity for more information on backend_types. Some
   backend_types do not accumulate I/O operation statistics and will not
   be included in the view.

   object text

   Target object of an I/O operation. Possible values are:
     * relation: Permanent relations.
     * temp relation: Temporary relations.
     * wal: Write Ahead Logs.

   context text

   The context of an I/O operation. Possible values are:
     * normal: The default or standard context for a type of I/O
       operation. For example, by default, relation data is read into and
       written out from shared buffers. Thus, reads and writes of relation
       data to and from shared buffers are tracked in context normal.
     * init: I/O operations performed while creating the WAL segments are
       tracked in context init.
     * vacuum: I/O operations performed outside of shared buffers while
       vacuuming and analyzing permanent relations. Temporary table
       vacuums use the same local buffer pool as other temporary table I/O
       operations and are tracked in context normal.
     * bulkread: Certain large read I/O operations done outside of shared
       buffers, for example, a sequential scan of a large table.
     * bulkwrite: Certain large write I/O operations done outside of
       shared buffers, such as COPY.

   reads bigint

   Number of read operations.

   read_bytes numeric

   The total size of read operations in bytes.

   read_time double precision

   Time spent waiting for read operations in milliseconds (if
   track_io_timing is enabled and object is not wal, or if
   track_wal_io_timing is enabled and object is wal, otherwise zero)

   writes bigint

   Number of write operations.

   write_bytes numeric

   The total size of write operations in bytes.

   write_time double precision

   Time spent waiting for write operations in milliseconds (if
   track_io_timing is enabled and object is not wal, or if
   track_wal_io_timing is enabled and object is wal, otherwise zero)

   writebacks bigint

   Number of units of size BLCKSZ (typically 8kB) which the process
   requested the kernel write out to permanent storage.

   writeback_time double precision

   Time spent waiting for writeback operations in milliseconds (if
   track_io_timing is enabled, otherwise zero). This includes the time
   spent queueing write-out requests and, potentially, the time spent to
   write out the dirty data.

   extends bigint

   Number of relation extend operations.

   extend_bytes numeric

   The total size of relation extend operations in bytes.

   extend_time double precision

   Time spent waiting for extend operations in milliseconds. (if
   track_io_timing is enabled and object is not wal, or if
   track_wal_io_timing is enabled and object is wal, otherwise zero)

   hits bigint

   The number of times a desired block was found in a shared buffer.

   evictions bigint

   Number of times a block has been written out from a shared or local
   buffer in order to make it available for another use.

   In context normal, this counts the number of times a block was evicted
   from a buffer and replaced with another block. In contexts bulkwrite,
   bulkread, and vacuum, this counts the number of times a block was
   evicted from shared buffers in order to add the shared buffer to a
   separate, size-limited ring buffer for use in a bulk I/O operation.

   reuses bigint

   The number of times an existing buffer in a size-limited ring buffer
   outside of shared buffers was reused as part of an I/O operation in the
   bulkread, bulkwrite, or vacuum contexts.

   fsyncs bigint

   Number of fsync calls. These are only tracked in context normal.

   fsync_time double precision

   Time spent waiting for fsync operations in milliseconds (if
   track_io_timing is enabled and object is not wal, or if
   track_wal_io_timing is enabled and object is wal, otherwise zero)

   stats_reset timestamp with time zone

   Time at which these statistics were last reset.

   Some backend types never perform I/O operations on some I/O objects
   and/or in some I/O contexts. These rows are omitted from the view. For
   example, the checkpointer does not checkpoint temporary tables, so
   there will be no rows for backend_type checkpointer and object temp
   relation.

   In addition, some I/O operations will never be performed either by
   certain backend types or on certain I/O objects and/or in certain I/O
   contexts. These cells will be NULL. For example, temporary tables are
   not fsynced, so fsyncs will be NULL for object temp relation. Also, the
   background writer does not perform reads, so reads will be NULL in rows
   for backend_type background writer.

   For the object wal, fsyncs and fsync_time track the fsync activity of
   WAL files done in issue_xlog_fsync. writes and write_time track the
   write activity of WAL files done in XLogWrite. See Section 28.5 for
   more information.

   pg_stat_io can be used to inform database tuning. For example:
     * A high evictions count can indicate that shared buffers should be
       increased.
     * Client backends rely on the checkpointer to ensure data is
       persisted to permanent storage. Large numbers of fsyncs by client
       backends could indicate a misconfiguration of shared buffers or of
       the checkpointer. More information on configuring the checkpointer
       can be found in Section 28.5.
     * Normally, client backends should be able to rely on auxiliary
       processes like the checkpointer and the background writer to write
       out dirty data as much as possible. Large numbers of writes by
       client backends could indicate a misconfiguration of shared buffers
       or of the checkpointer. More information on configuring the
       checkpointer can be found in Section 28.5.

Note

   Columns tracking I/O wait time will only be non-zero when
   track_io_timing is enabled. The user should be careful when referencing
   these columns in combination with their corresponding I/O operations in
   case track_io_timing was not enabled for the entire time since the last
   stats reset.

27.2.14. pg_stat_bgwriter #

   The pg_stat_bgwriter view will always have a single row, containing
   data about the background writer of the cluster.

   Table 27.24. pg_stat_bgwriter View

   Column Type

   Description

   buffers_clean bigint

   Number of buffers written by the background writer

   maxwritten_clean bigint

   Number of times the background writer stopped a cleaning scan because
   it had written too many buffers

   buffers_alloc bigint

   Number of buffers allocated

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

27.2.15. pg_stat_checkpointer #

   The pg_stat_checkpointer view will always have a single row, containing
   data about the checkpointer process of the cluster.

   Table 27.25. pg_stat_checkpointer View

   Column Type

   Description

   num_timed bigint

   Number of scheduled checkpoints due to timeout

   num_requested bigint

   Number of requested checkpoints

   num_done bigint

   Number of checkpoints that have been performed

   restartpoints_timed bigint

   Number of scheduled restartpoints due to timeout or after a failed
   attempt to perform it

   restartpoints_req bigint

   Number of requested restartpoints

   restartpoints_done bigint

   Number of restartpoints that have been performed

   write_time double precision

   Total amount of time that has been spent in the portion of processing
   checkpoints and restartpoints where files are written to disk, in
   milliseconds

   sync_time double precision

   Total amount of time that has been spent in the portion of processing
   checkpoints and restartpoints where files are synchronized to disk, in
   milliseconds

   buffers_written bigint

   Number of shared buffers written during checkpoints and restartpoints

   slru_written bigint

   Number of SLRU buffers written during checkpoints and restartpoints

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

   Checkpoints may be skipped if the server has been idle since the last
   one. num_timed and num_requested count both completed and skipped
   checkpoints, while num_done tracks only the completed ones. Similarly,
   restartpoints may be skipped if the last replayed checkpoint record is
   already the last restartpoint. restartpoints_timed and
   restartpoints_req count both completed and skipped restartpoints, while
   restartpoints_done tracks only the completed ones.

27.2.16. pg_stat_wal #

   The pg_stat_wal view will always have a single row, containing data
   about WAL activity of the cluster.

   Table 27.26. pg_stat_wal View

   Column Type

   Description

   wal_records bigint

   Total number of WAL records generated

   wal_fpi bigint

   Total number of WAL full page images generated

   wal_bytes numeric

   Total amount of WAL generated in bytes

   wal_buffers_full bigint

   Number of times WAL data was written to disk because WAL buffers became
   full

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

27.2.17. pg_stat_database #

   The pg_stat_database view will contain one row for each database in the
   cluster, plus one for shared objects, showing database-wide statistics.

   Table 27.27. pg_stat_database View

   Column Type

   Description

   datid oid

   OID of this database, or 0 for objects belonging to a shared relation

   datname name

   Name of this database, or NULL for shared objects.

   numbackends integer

   Number of backends currently connected to this database, or NULL for
   shared objects. This is the only column in this view that returns a
   value reflecting current state; all other columns return the
   accumulated values since the last reset.

   xact_commit bigint

   Number of transactions in this database that have been committed

   xact_rollback bigint

   Number of transactions in this database that have been rolled back

   blks_read bigint

   Number of disk blocks read in this database

   blks_hit bigint

   Number of times disk blocks were found already in the buffer cache, so
   that a read was not necessary (this only includes hits in the
   PostgreSQL buffer cache, not the operating system's file system cache)

   tup_returned bigint

   Number of live rows fetched by sequential scans and index entries
   returned by index scans in this database

   tup_fetched bigint

   Number of live rows fetched by index scans in this database

   tup_inserted bigint

   Number of rows inserted by queries in this database

   tup_updated bigint

   Number of rows updated by queries in this database

   tup_deleted bigint

   Number of rows deleted by queries in this database

   conflicts bigint

   Number of queries canceled due to conflicts with recovery in this
   database. (Conflicts occur only on standby servers; see
   pg_stat_database_conflicts for details.)

   temp_files bigint

   Number of temporary files created by queries in this database. All
   temporary files are counted, regardless of why the temporary file was
   created (e.g., sorting or hashing), and regardless of the
   log_temp_files setting.

   temp_bytes bigint

   Total amount of data written to temporary files by queries in this
   database. All temporary files are counted, regardless of why the
   temporary file was created, and regardless of the log_temp_files
   setting.

   deadlocks bigint

   Number of deadlocks detected in this database

   checksum_failures bigint

   Number of data page checksum failures detected in this database (or on
   a shared object), or NULL if data checksums are disabled.

   checksum_last_failure timestamp with time zone

   Time at which the last data page checksum failure was detected in this
   database (or on a shared object), or NULL if data checksums are
   disabled.

   blk_read_time double precision

   Time spent reading data file blocks by backends in this database, in
   milliseconds (if track_io_timing is enabled, otherwise zero)

   blk_write_time double precision

   Time spent writing data file blocks by backends in this database, in
   milliseconds (if track_io_timing is enabled, otherwise zero)

   session_time double precision

   Time spent by database sessions in this database, in milliseconds (note
   that statistics are only updated when the state of a session changes,
   so if sessions have been idle for a long time, this idle time won't be
   included)

   active_time double precision

   Time spent executing SQL statements in this database, in milliseconds
   (this corresponds to the states active and fastpath function call in
   pg_stat_activity)

   idle_in_transaction_time double precision

   Time spent idling while in a transaction in this database, in
   milliseconds (this corresponds to the states idle in transaction and
   idle in transaction (aborted) in pg_stat_activity)

   sessions bigint

   Total number of sessions established to this database

   sessions_abandoned bigint

   Number of database sessions to this database that were terminated
   because connection to the client was lost

   sessions_fatal bigint

   Number of database sessions to this database that were terminated by
   fatal errors

   sessions_killed bigint

   Number of database sessions to this database that were terminated by
   operator intervention

   parallel_workers_to_launch bigint

   Number of parallel workers planned to be launched by queries on this
   database

   parallel_workers_launched bigint

   Number of parallel workers launched by queries on this database

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

27.2.18. pg_stat_database_conflicts #

   The pg_stat_database_conflicts view will contain one row per database,
   showing database-wide statistics about query cancels occurring due to
   conflicts with recovery on standby servers. This view will only contain
   information on standby servers, since conflicts do not occur on primary
   servers.

   Table 27.28. pg_stat_database_conflicts View

   Column Type

   Description

   datid oid

   OID of a database

   datname name

   Name of this database

   confl_tablespace bigint

   Number of queries in this database that have been canceled due to
   dropped tablespaces

   confl_lock bigint

   Number of queries in this database that have been canceled due to lock
   timeouts

   confl_snapshot bigint

   Number of queries in this database that have been canceled due to old
   snapshots

   confl_bufferpin bigint

   Number of queries in this database that have been canceled due to
   pinned buffers

   confl_deadlock bigint

   Number of queries in this database that have been canceled due to
   deadlocks

   confl_active_logicalslot bigint

   Number of uses of logical slots in this database that have been
   canceled due to old snapshots or too low a wal_level on the primary

27.2.19. pg_stat_all_tables #

   The pg_stat_all_tables view will contain one row for each table in the
   current database (including TOAST tables), showing statistics about
   accesses to that specific table. The pg_stat_user_tables and
   pg_stat_sys_tables views contain the same information, but filtered to
   only show user and system tables respectively.

   Table 27.29. pg_stat_all_tables View

   Column Type

   Description

   relid oid

   OID of a table

   schemaname name

   Name of the schema that this table is in

   relname name

   Name of this table

   seq_scan bigint

   Number of sequential scans initiated on this table

   last_seq_scan timestamp with time zone

   The time of the last sequential scan on this table, based on the most
   recent transaction stop time

   seq_tup_read bigint

   Number of live rows fetched by sequential scans

   idx_scan bigint

   Number of index scans initiated on this table

   last_idx_scan timestamp with time zone

   The time of the last index scan on this table, based on the most recent
   transaction stop time

   idx_tup_fetch bigint

   Number of live rows fetched by index scans

   n_tup_ins bigint

   Total number of rows inserted

   n_tup_upd bigint

   Total number of rows updated. (This includes row updates counted in
   n_tup_hot_upd and n_tup_newpage_upd, and remaining non-HOT updates.)

   n_tup_del bigint

   Total number of rows deleted

   n_tup_hot_upd bigint

   Number of rows HOT updated. These are updates where no successor
   versions are required in indexes.

   n_tup_newpage_upd bigint

   Number of rows updated where the successor version goes onto a new heap
   page, leaving behind an original version with a t_ctid field that
   points to a different heap page. These are always non-HOT updates.

   n_live_tup bigint

   Estimated number of live rows

   n_dead_tup bigint

   Estimated number of dead rows

   n_mod_since_analyze bigint

   Estimated number of rows modified since this table was last analyzed

   n_ins_since_vacuum bigint

   Estimated number of rows inserted since this table was last vacuumed
   (not counting VACUUM FULL)

   last_vacuum timestamp with time zone

   Last time at which this table was manually vacuumed (not counting
   VACUUM FULL)

   last_autovacuum timestamp with time zone

   Last time at which this table was vacuumed by the autovacuum daemon

   last_analyze timestamp with time zone

   Last time at which this table was manually analyzed

   last_autoanalyze timestamp with time zone

   Last time at which this table was analyzed by the autovacuum daemon

   vacuum_count bigint

   Number of times this table has been manually vacuumed (not counting
   VACUUM FULL)

   autovacuum_count bigint

   Number of times this table has been vacuumed by the autovacuum daemon

   analyze_count bigint

   Number of times this table has been manually analyzed

   autoanalyze_count bigint

   Number of times this table has been analyzed by the autovacuum daemon

   total_vacuum_time double precision

   Total time this table has been manually vacuumed, in milliseconds (not
   counting VACUUM FULL). (This includes the time spent sleeping due to
   cost-based delays.)

   total_autovacuum_time double precision

   Total time this table has been vacuumed by the autovacuum daemon, in
   milliseconds. (This includes the time spent sleeping due to cost-based
   delays.)

   total_analyze_time double precision

   Total time this table has been manually analyzed, in milliseconds.
   (This includes the time spent sleeping due to cost-based delays.)

   total_autoanalyze_time double precision

   Total time this table has been analyzed by the autovacuum daemon, in
   milliseconds. (This includes the time spent sleeping due to cost-based
   delays.)

27.2.20. pg_stat_all_indexes #

   The pg_stat_all_indexes view will contain one row for each index in the
   current database, showing statistics about accesses to that specific
   index. The pg_stat_user_indexes and pg_stat_sys_indexes views contain
   the same information, but filtered to only show user and system indexes
   respectively.

   Table 27.30. pg_stat_all_indexes View

   Column Type

   Description

   relid oid

   OID of the table for this index

   indexrelid oid

   OID of this index

   schemaname name

   Name of the schema this index is in

   relname name

   Name of the table for this index

   indexrelname name

   Name of this index

   idx_scan bigint

   Number of index scans initiated on this index

   last_idx_scan timestamp with time zone

   The time of the last scan on this index, based on the most recent
   transaction stop time

   idx_tup_read bigint

   Number of index entries returned by scans on this index

   idx_tup_fetch bigint

   Number of live table rows fetched by simple index scans using this
   index

   Indexes can be used by simple index scans, “bitmap” index scans, and
   the optimizer. In a bitmap scan the output of several indexes can be
   combined via AND or OR rules, so it is difficult to associate
   individual heap row fetches with specific indexes when a bitmap scan is
   used. Therefore, a bitmap scan increments the
   pg_stat_all_indexes.idx_tup_read count(s) for the index(es) it uses,
   and it increments the pg_stat_all_tables.idx_tup_fetch count for the
   table, but it does not affect pg_stat_all_indexes.idx_tup_fetch. The
   optimizer also accesses indexes to check for supplied constants whose
   values are outside the recorded range of the optimizer statistics
   because the optimizer statistics might be stale.

Note

   The idx_tup_read and idx_tup_fetch counts can be different even without
   any use of bitmap scans, because idx_tup_read counts index entries
   retrieved from the index while idx_tup_fetch counts live rows fetched
   from the table. The latter will be less if any dead or
   not-yet-committed rows are fetched using the index, or if any heap
   fetches are avoided by means of an index-only scan.

Note

   Index scans may sometimes perform multiple index searches per
   execution. Each index search increments pg_stat_all_indexes.idx_scan,
   so it's possible for the count of index scans to significantly exceed
   the total number of index scan executor node executions.

   This can happen with queries that use certain SQL constructs to search
   for rows matching any value out of a list or array of multiple scalar
   values (see Section 9.25). It can also happen to queries with a
   column_name = value1 OR column_name = value2 ... construct, though only
   when the optimizer transforms the construct into an equivalent
   multi-valued array representation. Similarly, when B-tree index scans
   use the skip scan optimization, an index search is performed each time
   the scan is repositioned to the next index leaf page that might have
   matching tuples (see Section 11.3).

Tip

   EXPLAIN ANALYZE outputs the total number of index searches performed by
   each index scan node. See Section 14.1.2 for an example demonstrating
   how this works.

27.2.21. pg_statio_all_tables #

   The pg_statio_all_tables view will contain one row for each table in
   the current database (including TOAST tables), showing statistics about
   I/O on that specific table. The pg_statio_user_tables and
   pg_statio_sys_tables views contain the same information, but filtered
   to only show user and system tables respectively.

   Table 27.31. pg_statio_all_tables View

   Column Type

   Description

   relid oid

   OID of a table

   schemaname name

   Name of the schema that this table is in

   relname name

   Name of this table

   heap_blks_read bigint

   Number of disk blocks read from this table

   heap_blks_hit bigint

   Number of buffer hits in this table

   idx_blks_read bigint

   Number of disk blocks read from all indexes on this table

   idx_blks_hit bigint

   Number of buffer hits in all indexes on this table

   toast_blks_read bigint

   Number of disk blocks read from this table's TOAST table (if any)

   toast_blks_hit bigint

   Number of buffer hits in this table's TOAST table (if any)

   tidx_blks_read bigint

   Number of disk blocks read from this table's TOAST table indexes (if
   any)

   tidx_blks_hit bigint

   Number of buffer hits in this table's TOAST table indexes (if any)

27.2.22. pg_statio_all_indexes #

   The pg_statio_all_indexes view will contain one row for each index in
   the current database, showing statistics about I/O on that specific
   index. The pg_statio_user_indexes and pg_statio_sys_indexes views
   contain the same information, but filtered to only show user and system
   indexes respectively.

   Table 27.32. pg_statio_all_indexes View

   Column Type

   Description

   relid oid

   OID of the table for this index

   indexrelid oid

   OID of this index

   schemaname name

   Name of the schema this index is in

   relname name

   Name of the table for this index

   indexrelname name

   Name of this index

   idx_blks_read bigint

   Number of disk blocks read from this index

   idx_blks_hit bigint

   Number of buffer hits in this index

27.2.23. pg_statio_all_sequences #

   The pg_statio_all_sequences view will contain one row for each sequence
   in the current database, showing statistics about I/O on that specific
   sequence.

   Table 27.33. pg_statio_all_sequences View

   Column Type

   Description

   relid oid

   OID of a sequence

   schemaname name

   Name of the schema this sequence is in

   relname name

   Name of this sequence

   blks_read bigint

   Number of disk blocks read from this sequence

   blks_hit bigint

   Number of buffer hits in this sequence

27.2.24. pg_stat_user_functions #

   The pg_stat_user_functions view will contain one row for each tracked
   function, showing statistics about executions of that function. The
   track_functions parameter controls exactly which functions are tracked.

   Table 27.34. pg_stat_user_functions View

   Column Type

   Description

   funcid oid

   OID of a function

   schemaname name

   Name of the schema this function is in

   funcname name

   Name of this function

   calls bigint

   Number of times this function has been called

   total_time double precision

   Total time spent in this function and all other functions called by it,
   in milliseconds

   self_time double precision

   Total time spent in this function itself, not including other functions
   called by it, in milliseconds

27.2.25. pg_stat_slru #

   PostgreSQL accesses certain on-disk information via SLRU (simple
   least-recently-used) caches. The pg_stat_slru view will contain one row
   for each tracked SLRU cache, showing statistics about access to cached
   pages.

   For each SLRU cache that's part of the core server, there is a
   configuration parameter that controls its size, with the suffix
   _buffers appended.

   Table 27.35. pg_stat_slru View

   Column Type

   Description

   name text

   Name of the SLRU

   blks_zeroed bigint

   Number of blocks zeroed during initializations

   blks_hit bigint

   Number of times disk blocks were found already in the SLRU, so that a
   read was not necessary (this only includes hits in the SLRU, not the
   operating system's file system cache)

   blks_read bigint

   Number of disk blocks read for this SLRU

   blks_written bigint

   Number of disk blocks written for this SLRU

   blks_exists bigint

   Number of blocks checked for existence for this SLRU

   flushes bigint

   Number of flushes of dirty data for this SLRU

   truncates bigint

   Number of truncates for this SLRU

   stats_reset timestamp with time zone

   Time at which these statistics were last reset

27.2.26. Statistics Functions #

   Other ways of looking at the statistics can be set up by writing
   queries that use the same underlying statistics access functions used
   by the standard views shown above. For details such as the functions'
   names, consult the definitions of the standard views. (For example, in
   psql you could issue \d+ pg_stat_activity.) The access functions for
   per-database statistics take a database OID as an argument to identify
   which database to report on. The per-table and per-index functions take
   a table or index OID. The functions for per-function statistics take a
   function OID. Note that only tables, indexes, and functions in the
   current database can be seen with these functions.

   Additional functions related to the cumulative statistics system are
   listed in Table 27.36.

   Table 27.36. Additional Statistics Functions

   Function

   Description

   pg_backend_pid () → integer

   Returns the process ID of the server process attached to the current
   session.

   pg_stat_get_backend_io ( integer ) → setof record

   Returns I/O statistics about the backend with the specified process ID.
   The output fields are exactly the same as the ones in the pg_stat_io
   view.

   The function does not return I/O statistics for the checkpointer, the
   background writer, the startup process and the autovacuum launcher as
   they are already visible in the pg_stat_io view and there is only one
   of each.

   pg_stat_get_activity ( integer ) → setof record

   Returns a record of information about the backend with the specified
   process ID, or one record for each active backend in the system if NULL
   is specified. The fields returned are a subset of those in the
   pg_stat_activity view.

   pg_stat_get_backend_wal ( integer ) → record

   Returns WAL statistics about the backend with the specified process ID.
   The output fields are exactly the same as the ones in the pg_stat_wal
   view.

   The function does not return WAL statistics for the checkpointer, the
   background writer, the startup process and the autovacuum launcher.

   pg_stat_get_snapshot_timestamp () → timestamp with time zone

   Returns the timestamp of the current statistics snapshot, or NULL if no
   statistics snapshot has been taken. A snapshot is taken the first time
   cumulative statistics are accessed in a transaction if
   stats_fetch_consistency is set to snapshot

   pg_stat_get_xact_blocks_fetched ( oid ) → bigint

   Returns the number of block read requests for table or index, in the
   current transaction. This number minus pg_stat_get_xact_blocks_hit
   gives the number of kernel read() calls; the number of actual physical
   reads is usually lower due to kernel-level buffering.

   pg_stat_get_xact_blocks_hit ( oid ) → bigint

   Returns the number of block read requests for table or index, in the
   current transaction, found in cache (not triggering kernel read()
   calls).

   pg_stat_clear_snapshot () → void

   Discards the current statistics snapshot or cached information.

   pg_stat_reset () → void

   Resets all statistics counters for the current database to zero.

   This function is restricted to superusers by default, but other users
   can be granted EXECUTE to run the function.

   pg_stat_reset_shared ( [ target text DEFAULT NULL ] ) → void

   Resets some cluster-wide statistics counters to zero, depending on the
   argument. target can be:
     * archiver: Reset all the counters shown in the pg_stat_archiver
       view.
     * bgwriter: Reset all the counters shown in the pg_stat_bgwriter
       view.
     * checkpointer: Reset all the counters shown in the
       pg_stat_checkpointer view.
     * io: Reset all the counters shown in the pg_stat_io view.
     * recovery_prefetch: Reset all the counters shown in the
       pg_stat_recovery_prefetch view.
     * slru: Reset all the counters shown in the pg_stat_slru view.
     * wal: Reset all the counters shown in the pg_stat_wal view.
     * NULL or not specified: All the counters from the views listed above
       are reset.

   This function is restricted to superusers by default, but other users
   can be granted EXECUTE to run the function.

   pg_stat_reset_single_table_counters ( oid ) → void

   Resets statistics for a single table or index in the current database
   or shared across all databases in the cluster to zero.

   This function is restricted to superusers by default, but other users
   can be granted EXECUTE to run the function.

   pg_stat_reset_backend_stats ( integer ) → void

   Resets statistics for a single backend with the specified process ID to
   zero.

   This function is restricted to superusers by default, but other users
   can be granted EXECUTE to run the function.

   pg_stat_reset_single_function_counters ( oid ) → void

   Resets statistics for a single function in the current database to
   zero.

   This function is restricted to superusers by default, but other users
   can be granted EXECUTE to run the function.

   pg_stat_reset_slru ( [ target text DEFAULT NULL ] ) → void

   Resets statistics to zero for a single SLRU cache, or for all SLRUs in
   the cluster. If target is NULL or is not specified, all the counters
   shown in the pg_stat_slru view for all SLRU caches are reset. The
   argument can be one of commit_timestamp, multixact_member,
   multixact_offset, notify, serializable, subtransaction, or transaction
   to reset the counters for only that entry. If the argument is other (or
   indeed, any unrecognized name), then the counters for all other SLRU
   caches, such as extension-defined caches, are reset.

   This function is restricted to superusers by default, but other users
   can be granted EXECUTE to run the function.

   pg_stat_reset_replication_slot ( text ) → void

   Resets statistics of the replication slot defined by the argument. If
   the argument is NULL, resets statistics for all the replication slots.

   This function is restricted to superusers by default, but other users
   can be granted EXECUTE to run the function.

   pg_stat_reset_subscription_stats ( oid ) → void

   Resets statistics for a single subscription shown in the
   pg_stat_subscription_stats view to zero. If the argument is NULL, reset
   statistics for all subscriptions.

   This function is restricted to superusers by default, but other users
   can be granted EXECUTE to run the function.

Warning

   Using pg_stat_reset() also resets counters that autovacuum uses to
   determine when to trigger a vacuum or an analyze. Resetting these
   counters can cause autovacuum to not perform necessary work, which can
   cause problems such as table bloat or out-dated table statistics. A
   database-wide ANALYZE is recommended after the statistics have been
   reset.

   pg_stat_get_activity, the underlying function of the pg_stat_activity
   view, returns a set of records containing all the available information
   about each backend process. Sometimes it may be more convenient to
   obtain just a subset of this information. In such cases, another set of
   per-backend statistics access functions can be used; these are shown in
   Table 27.37. These access functions use the session's backend ID
   number, which is a small integer (>= 0) that is distinct from the
   backend ID of any concurrent session, although a session's ID can be
   recycled as soon as it exits. The backend ID is used, among other
   things, to identify the session's temporary schema if it has one. The
   function pg_stat_get_backend_idset provides a convenient way to list
   all the active backends' ID numbers for invoking these functions. For
   example, to show the PIDs and current queries of all backends:
SELECT pg_stat_get_backend_pid(backendid) AS pid,
       pg_stat_get_backend_activity(backendid) AS query
FROM pg_stat_get_backend_idset() AS backendid;

   Table 27.37. Per-Backend Statistics Functions

   Function

   Description

   pg_stat_get_backend_activity ( integer ) → text

   Returns the text of this backend's most recent query.

   pg_stat_get_backend_activity_start ( integer ) → timestamp with time
   zone

   Returns the time when the backend's most recent query was started.

   pg_stat_get_backend_client_addr ( integer ) → inet

   Returns the IP address of the client connected to this backend.

   pg_stat_get_backend_client_port ( integer ) → integer

   Returns the TCP port number that the client is using for communication.

   pg_stat_get_backend_dbid ( integer ) → oid

   Returns the OID of the database this backend is connected to.

   pg_stat_get_backend_idset () → setof integer

   Returns the set of currently active backend ID numbers.

   pg_stat_get_backend_pid ( integer ) → integer

   Returns the process ID of this backend.

   pg_stat_get_backend_start ( integer ) → timestamp with time zone

   Returns the time when this process was started.

   pg_stat_get_backend_subxact ( integer ) → record

   Returns a record of information about the subtransactions of the
   backend with the specified ID. The fields returned are subxact_count,
   which is the number of subtransactions in the backend's subtransaction
   cache, and subxact_overflow, which indicates whether the backend's
   subtransaction cache is overflowed or not.

   pg_stat_get_backend_userid ( integer ) → oid

   Returns the OID of the user logged into this backend.

   pg_stat_get_backend_wait_event ( integer ) → text

   Returns the wait event name if this backend is currently waiting,
   otherwise NULL. See Table 27.5 through Table 27.13.

   pg_stat_get_backend_wait_event_type ( integer ) → text

   Returns the wait event type name if this backend is currently waiting,
   otherwise NULL. See Table 27.4 for details.

   pg_stat_get_backend_xact_start ( integer ) → timestamp with time zone

   Returns the time when the backend's current transaction was started.