27.2. The Cumulative Statistics System

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27.2. The Cumulative Statistics System #

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.
WalReceiverUpstreamCatchup Waiting for upstream server WAL flush position to catch up to requested start point.
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

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