28.2. 統計資訊收集器
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.
28.2.1. 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 20 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_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 and write times.
The parameter track_wal_io_timing enables monitoring of WAL write 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.
28.2.2. Viewing Statistics
Several predefined views, listed in Table 28.1, are available to show the current state of the system. There are also several other views, listed in Table 28.2, available to show the accumulated statistics. Alternatively, one can build custom views using the underlying cumulative statistics functions, as discussed in Section 28.2.24.
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 28.1 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
(see also Section 22.5) can see all the information about all sessions.
Table 28.1. Dynamic Statistics Views
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 28.4.1.
pg_stat_progress_create_index
One row for each backend running CREATE INDEX
or REINDEX
, showing current progress. See Section 28.4.2.
pg_stat_progress_vacuum
One row for each backend (including autovacuum worker processes) running VACUUM
, showing current progress. See Section 28.4.3.
pg_stat_progress_cluster
One row for each backend running CLUSTER
or VACUUM FULL
, showing current progress. See Section 28.4.4.
pg_stat_progress_basebackup
One row for each WAL sender process streaming a base backup, showing current progress. See Section 28.4.5.
pg_stat_progress_copy
One row for each backend running COPY
, showing current progress. See Section 28.4.6.
Table 28.2. Collected Statistics Views
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_wal
One row only, showing statistics about WAL activity. See pg_stat_wal
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_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_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.
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_stat_slru
One row per SLRU, showing statistics of operations. See pg_stat_slru
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_subscription_stats
One row per subscription, showing statistics about errors. See pg_stat_subscription_stats
for details.
The per-index statistics are particularly useful to determine which indexes are being used and how effective they are.
The pg_statio_
views are primarily useful to determine the effectiveness of the buffer cache. When the number of actual disk reads is much smaller than the number of buffer hits, then the cache is satisfying most read requests without invoking a kernel call. However, these statistics do not give the entire story: due to the way in which PostgreSQL handles disk I/O, data that is not in the PostgreSQL buffer cache might still reside in the kernel's I/O cache, and might therefore still be fetched without requiring a physical read. Users interested in obtaining more detailed information on PostgreSQL I/O behavior are advised to use the PostgreSQL statistics views in combination with operating system utilities that allow insight into the kernel's handling of I/O.
28.2.3. pg_stat_activity
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 28.3. pg_stat_activity
View
pg_stat_activity
ViewColumn 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. NULL
if this process is a parallel group leader or does not participate in parallel query.
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 28.4.
wait_event
text
Wait event name if backend is currently waiting, otherwise NULL. See Table 28.5 through Table 28.13.
state
text
Current overall state of this backend. Possible values are:
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 toidle 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.
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
, startup
, walreceiver
, walsender
and walwriter
. 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.
Table 28.4. Wait Event Types
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 28.5.
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 28.6.
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 28.7.
Extension
The server process is waiting for some condition defined by an extension module. See Table 28.8.
IO
The server process is waiting for an I/O operation to complete. wait_event
will identify the specific wait point; see Table 28.9.
IPC
The server process is waiting for some interaction with another server process. wait_event
will identify the specific wait point; see Table 28.10.
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 28.11.
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 28.12.
Timeout
The server process is waiting for a timeout to expire. wait_event
will identify the specific wait point; see Table 28.13.
Table 28.5. Wait Events of Type Activity
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.
LogicalApplyMain
Waiting in main loop of logical replication apply process.
LogicalLauncherMain
Waiting in main loop of logical replication launcher process.
RecoveryWalStream
Waiting in main loop of startup process for WAL to arrive, during streaming recovery.
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.
WalWriterMain
Waiting in main loop of WAL writer process.
Table 28.6. Wait Events of Type BufferPin
BufferPin
BufferPin
Wait Event
Description
BufferPin
Waiting to acquire an exclusive pin on a buffer.
Table 28.7. Wait Events of Type Client
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.
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 28.8. Wait Events of Type Extension
Extension
Extension
Wait Event
Description
Extension
Waiting in an extension.
Table 28.9. Wait Events of Type IO
IO
IO
Wait Event
Description
BaseBackupRead
Waiting for base backup to read from a file.
BufFileRead
Waiting for a read from a buffered file.
BufFileWrite
Waiting for a write to a buffered file.
BufFileTruncate
Waiting for a buffered file to be truncated.
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.
CopyFileRead
Waiting for a read during a file copy operation.
CopyFileWrite
Waiting for a write during a file copy operation.
DSMFillZeroWrite
Waiting to fill a dynamic shared memory backing file with zeroes.
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.
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.
RelationMapSync
Waiting for the relation map file to reach durable storage.
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.
VersionFileWrite
Waiting for the version file to be written while creating a database.
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.
WALSenderTimelineHistoryRead
Waiting for a read from a timeline history file during a walsender timeline command.
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 28.10. Wait Events of Type IPC
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.
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.
HashGrowBatchesAllocate
Waiting for an elected Parallel Hash participant to allocate more batches.
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.
HashGrowBatchesRepartition
Waiting for other Parallel Hash participants to finish repartitioning.
HashGrowBucketsAllocate
Waiting for an elected Parallel Hash participant to finish allocating more buckets.
HashGrowBucketsElect
Waiting to elect a Parallel Hash participant to allocate more buckets.
HashGrowBucketsReinsert
Waiting for other Parallel Hash participants to finish inserting tuples into new buckets.
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.
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 end of a parallel operation.
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.
XactGroupUpdate
Waiting for the group leader to update transaction status at end of a parallel operation.
Table 28.11. Wait Events of Type Lock
Lock
Lock
Wait Event
Description
advisory
Waiting to acquire an advisory user lock.
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.
Table 28.12. Wait Events of Type LWLock
LWLock
LWLock
Wait Event
Description
AddinShmemInit
Waiting to manage an extension's space allocation in shared memory.
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