27.2. 統計資訊收集器
版本:11
PostgreSQL 的統計資訊收集器是一個子系統,支援收集和回報有關伺服器活動的資訊。目前,收集器可以以磁區和單個資料列的方式計算對資料表和索引的存取。它也追踪著每個資料表中的總資料筆數,以及有關每個資料表的清理和分析操作的資訊。它還可以計算對使用者定義函數的呼叫以及每個函數所花費的總時間。
PostgreSQL 也支援回報有關目前系統中確切正在發生情況的動態資訊,例如目前由其他伺服器程序執行的確切指令以及系統中存在哪些其他連線。此功能獨立於收集器程序。
27.2.1. Statistics Collection Configuration
由於收集統計資訊會增加查詢執行的成本,因此可以將系統配置為收集或不收集資訊。這由通常由 postgresql.conf 中的配置參數所控制。 (有關設定配置參數的詳細資訊,請參閱第 19 章。)
The parameter track_activities enables monitoring of the current command being executed by any server process.
The parameter track_counts controls whether 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.
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
.)
The statistics collector transmits the collected information to other PostgreSQL processes through temporary files. These files are stored in the directory named by the stats_temp_directory parameter, pg_stat_tmp
by default. For better performance, stats_temp_directory
can be pointed at a RAM-based file system, decreasing physical I/O requirements. When the server 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. When recovery is performed at server start (e.g. after immediate shutdown, server crash, 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 results of statistics collection. Alternatively, one can build custom views using the underlying statistics functions, as discussed in Section 27.2.3.
When using the statistics to monitor collected data, it is important to realize that the information does not update instantaneously. Each individual server process transmits new statistical counts to the collector just before going idle; so a query or transaction still in progress does not affect the displayed totals. Also, the collector itself emits a new report at most once per PGSTAT_STAT_INTERVAL
milliseconds (500 ms unless altered while building the server). So 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 these statistics, it first fetches the most recent report emitted by the collector process and then continues to use this snapshot for all statistical views and functions until the end of its current transaction. 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. But if you want to see new results with each query, be sure to do the queries outside any transaction block. Alternatively, you can invoke pg_stat_clear_snapshot
(), which will discard the current transaction's statistics snapshot (if any). The next use of statistical information will cause a new snapshot to be fetched.
A transaction can also see its own statistics (as yet untransmitted to the collector) 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 members of the built-in role pg_read_all_stats
(see also Section 21.5) 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_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_create_index
One row for each backend running CREATE INDEX
or REINDEX
, showing current progress. See Section 27.4.1.
pg_stat_progress_vacuum
One row for each backend (including autovacuum worker processes) running VACUUM
, showing current progress. See Section 27.4.2.
pg_stat_progress_cluster
One row for each backend running CLUSTER
or VACUUM FULL
, 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_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
).
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 collector in combination with operating system utilities that allow insight into the kernel's handling of I/O.
Table 27.3. 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
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
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. Possible values are:
LWLock
: The backend is waiting for a lightweight lock. Each such lock protects 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.)Lock
: The backend 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.BufferPin
: The server process is waiting to access to a data buffer during a period when no other process can be examining that buffer. Buffer pin waits can be protracted if another process holds an open cursor which last read data from the buffer in question.Activity
: The server process is idle. This is used by system processes waiting for activity in their main processing loop.wait_event
will identify the specific wait point.Extension
: The server process is waiting for activity in an extension module. This category is useful for modules to track custom waiting points.Client
: The server process is waiting for some activity on a socket from user applications, and that the server expects something to happen that is independent from its internal processes.wait_event
will identify the specific wait point.IPC
: The server process is waiting for some activity from another process in the server.wait_event
will identify the specific wait point.Timeout
: The server process is waiting for a timeout to expire.wait_event
will identify the specific wait point.IO
: The server process is waiting for a IO to complete.wait_event
will identify the specific wait point.
wait_event
text
Wait event name if backend is currently waiting, otherwise NULL. See Table 27.4for details.
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
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 characters; 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
, startup
, walreceiver
, walsender
and walwriter
. In addition, background workers registered by extensions may have additional types.
The pg_stat_activity
view will have one row per server process, showing information related to the current activity of that process.
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 27.4. wait_event
Description
wait_event
DescriptionWait Event Type
Wait Event Name
Description
LWLock
ShmemIndexLock
Waiting to find or allocate space in shared memory.
OidGenLock
Waiting to allocate or assign an OID.
XidGenLock
Waiting to allocate or assign a transaction id.
ProcArrayLock
Waiting to get a snapshot or clearing a transaction id at transaction end.
SInvalReadLock
Waiting to retrieve or remove messages from shared invalidation queue.
SInvalWriteLock
Waiting to add a message in shared invalidation queue.
WALBufMappingLock
Waiting to replace a page in WAL buffers.
WALWriteLock
Waiting for WAL buffers to be written to disk.
ControlFileLock
Waiting to read or update the control file or creation of a new WAL file.
CheckpointLock
Waiting to perform checkpoint.
CLogControlLock
Waiting to read or update transaction status.
SubtransControlLock
Waiting to read or update sub-transaction information.
MultiXactGenLock
Waiting to read or update shared multixact state.
MultiXactOffsetControlLock
Waiting to read or update multixact offset mappings.
MultiXactMemberControlLock
Waiting to read or update multixact member mappings.
RelCacheInitLock
Waiting to read or write relation cache initialization file.
CheckpointerCommLock
Waiting to manage fsync requests.
TwoPhaseStateLock
Waiting to read or update the state of prepared transactions.
TablespaceCreateLock
Waiting to create or drop the tablespace.
BtreeVacuumLock
Waiting to read or update vacuum-related information for a B-tree index.
AddinShmemInitLock
Waiting to manage space allocation in shared memory.
AutovacuumLock
Autovacuum worker or launcher waiting to update or read the current state of autovacuum workers.
AutovacuumScheduleLock
Waiting to ensure that the table it has selected for a vacuum still needs vacuuming.
SyncScanLock
Waiting to get the start location of a scan on a table for synchronized scans.
RelationMappingLock
Waiting to update the relation map file used to store catalog to filenode mapping.
AsyncCtlLock
Waiting to read or update shared notification state.
AsyncQueueLock
Waiting to read or update notification messages.
SerializableXactHashLock
Waiting to retrieve or store information about serializable transactions.
SerializableFinishedListLock
Waiting to access the list of finished serializable transactions.
SerializablePredicateLockListLock
Waiting to perform an operation on a list of locks held by serializable transactions.
OldSerXidLock
Waiting to read or record conflicting serializable transactions.
SyncRepLock
Waiting to read or update information about synchronous replicas.
BackgroundWorkerLock
Waiting to read or update background worker state.
DynamicSharedMemoryControlLock
Waiting to read or update dynamic shared memory state.
AutoFileLock
Waiting to update the postgresql.auto.conf
file.
ReplicationSlotAllocationLock
Waiting to allocate or free a replication slot.
ReplicationSlotControlLock
Waiting to read or update replication slot state.
CommitTsControlLock
Waiting to read or update transaction commit timestamps.
CommitTsLock
Waiting to read or update the last value set for the transaction timestamp.
ReplicationOriginLock
Waiting to setup, drop or use replication origin.
MultiXactTruncationLock
Waiting to read or truncate multixact information.
OldSnapshotTimeMapLock
Waiting to read or update old snapshot control information.
LogicalRepWorkerLock
Waiting for action on logical replication worker to finish.
CLogTruncationLock
Waiting to execute txid_status
or update the oldest transaction id available to it.
clog
Waiting for I/O on a clog (transaction status) buffer.
commit_timestamp
Waiting for I/O on commit timestamp buffer.
subtrans
Waiting for I/O a subtransaction buffer.
multixact_offset
Waiting for I/O on a multixact offset buffer.
multixact_member
Waiting for I/O on a multixact_member buffer.
async
Waiting for I/O on an async (notify) buffer.
oldserxid
Waiting for I/O on an oldserxid buffer.
wal_insert
Waiting to insert WAL into a memory buffer.
buffer_content
Waiting to read or write a data page in memory.
buffer_io
Waiting for I/O on a data page.
replication_origin
Waiting to read or update the replication progress.
replication_slot_io
Waiting for I/O on a replication slot.
proc
Waiting to read or update the fast-path lock information.
buffer_mapping
Waiting to associate a data block with a buffer in the buffer pool.
lock_manager
Waiting to add or examine locks for backends, or waiting to join or exit a locking group (used by parallel query).
predicate_lock_manager
Waiting to add or examine predicate lock information.
serializable_xact
Waiting to perform an operation on a serializable transaction in a parallel query.
parallel_query_dsa
Waiting for parallel query dynamic shared memory allocation lock.
tbm
Waiting for TBM shared iterator lock.
parallel_append
Waiting to choose the next subplan during Parallel Append plan execution.
parallel_hash_join
Waiting to allocate or exchange a chunk of memory or update counters during Parallel Hash plan execution.
Lock
relation
Waiting to acquire a lock on a relation.
extend
Waiting to extend a relation.
page
Waiting to acquire a lock on page of a relation.
tuple
Waiting to acquire a lock on a tuple.
transactionid
Waiting for a transaction to finish.
virtualxid
Waiting to acquire a virtual xid lock.
speculative token
Waiting to acquire a speculative insertion lock.
object
Waiting to acquire a lock on a non-relation database object.
userlock
Waiting to acquire a user lock.
advisory
Waiting to acquire an advisory user lock.
BufferPin
BufferPin
Waiting to acquire a pin on a buffer.
Activity
ArchiverMain
Waiting in main loop of the 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 background worker.
CheckpointerMain
Waiting in main loop of checkpointer process.
LogicalApplyMain
Waiting in main loop of logical apply process.
LogicalLauncherMain
Waiting in main loop of logical launcher process.
PgStatMain
Waiting in main loop of the statistics collector process.
RecoveryWalAll
Waiting for WAL from a stream at recovery.
RecoveryWalStream
Waiting when WAL data is not available from any kind of sources (local, archive or stream) before trying again to retrieve WAL data, at 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.
Client
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 the 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.
WalReceiverWaitStart
Waiting for startup process to send initial data for streaming replication.
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.
Extension
Extension
Waiting in an extension.
IPC
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.
CheckpointDone
Waiting for a checkpoint to complete.
CheckpointStart
Waiting for a checkpoint to start.
ClogGroupUpdate
Waiting for group leader to update transaction status at transaction end.
ExecuteGather
Waiting for activity from child process when executing Gather
node.
Hash/Batch/Allocating
Waiting for an elected Parallel Hash participant to allocate a hash table.
Hash/Batch/Electing
Electing a Parallel Hash participant to allocate a hash table.
Hash/Batch/Loading
Waiting for other Parallel Hash participants to finish loading a hash table.
Hash/Build/Allocating
Waiting for an elected Parallel Hash participant to allocate the initial hash table.
Hash/Build/Electing
Electing a Parallel Hash participant to allocate the initial hash table.
Hash/Build/HashingInner
Waiting for other Parallel Hash participants to finish hashing the inner relation.
Hash/Build/HashingOuter
Waiting for other Parallel Hash participants to finish partitioning the outer relation.
Hash/GrowBatches/Allocating
Waiting for an elected Parallel Hash participant to allocate more batches.
Hash/GrowBatches/Deciding
Electing a Parallel Hash participant to decide on future batch growth.
Hash/GrowBatches/Electing
Electing a Parallel Hash participant to allocate more batches.
Hash/GrowBatches/Finishing
Waiting for an elected Parallel Hash participant to decide on future batch growth.
Hash/GrowBatches/Repartitioning
Waiting for other Parallel Hash participants to finishing repartitioning.
Hash/GrowBuckets/Allocating
Waiting for an elected Parallel Hash participant to finish allocating more buckets.
Hash/GrowBuckets/Electing
Electing a Parallel Hash participant to allocate more buckets.
Hash/GrowBuckets/Reinserting
Waiting for other Parallel Hash participants to finish inserting tuples into new buckets.
LogicalSyncData
Waiting for logical replication remote server to send data for initial table synchronization.
LogicalSyncStateChange
Waiting for logical replication remote server to change state.
MessageQueueInternal
Waiting for other process to be attached in 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 group leader to clear transaction id at transaction end.
Promote
Waiting for standby promotion.
ReplicationOriginDrop
Waiting for a replication origin to become inactive to be dropped.
ReplicationSlotDrop
Waiting for a replication slot to become inactive to be dropped.
SafeSnapshot
Waiting for a snapshot for a READ ONLY DEFERRABLE
transaction.
SyncRep
Waiting for confirmation from remote server during synchronous replication.
Timeout
BaseBackupThrottle
Waiting during base backup when throttling activity.
PgSleep
Waiting in process that called pg_sleep
.
RecoveryApplyDelay
Waiting to apply WAL at recovery because it is delayed.
IO
BufFileRead
Waiting for a read from a buffered file.
BufFileWrite
Waiting for a write to a buffered file.
ControlFileRead
Waiting for a read from the control file.
ControlFileSync
Waiting for the control file to reach stable storage.
ControlFileSyncUpdate
Waiting for an update to the control file to reach stable storage.
ControlFileWrite
Waiting for a write to the control file.
ControlFileWriteUpdate
Waiting for a write to update the control file.
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 stable storage.
DataFileImmediateSync
Waiting for an immediate synchronization of a relation data file to stable 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 stable storage.
DataFileTruncate
Waiting for a relation data file to be truncated.
DataFileWrite
Waiting for a write to a relation data file.
DSMFillZeroWrite
Waiting to write zero bytes to a dynamic shared memory backing file.
LockFileAddToDataDirRead
Waiting for a read while adding a line to the data directory lock file.
LockFileAddToDataDirSync
Waiting for data to reach stable 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 stable 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 stable storage during a checkpoint.
LogicalRewriteMappingSync
Waiting for mapping data to reach stable 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 stable 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 stable 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 stable storage while restoring it to memory.
ReplicationSlotSync
Waiting for a replication slot control file to reach stable storage.
ReplicationSlotWrite
Waiting for a write to a replication slot control file.
SLRUFlushSync
Waiting for SLRU data to reach stable storage during a checkpoint or database shutdown.
SLRURead
Waiting for a read of an SLRU page.
SLRUSync
Waiting for SLRU data to reach stable 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 stable 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 stable 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 stable 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 stable storage.
TwophaseFileWrite
Waiting for a write of a two phase state file.
WALBootstrapSync
Waiting for WAL to reach stable 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 a new WAL segment created by copying an existing one to reach stable 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 stable 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 walsender timeline command.
WALSync
Waiting for a WAL file to reach stable storage.
WALSyncMethodAssign
Waiting for data to reach stable storage while assigning WAL sync method.
WALWrite
Waiting for a write to a WAL file.
Note
For tranches registered by extensions, the name is specified by extension and this will be displayed as wait_event
. It is quite possible that user has registered the tranche in one of the backends (by having allocation in dynamic shared memory) in which case other backends won't have that information, so we display extension
for such cases.
Here is an example of how wait events can be viewed
Table 27.5. pg_stat_replication
View
Column
Type
Description
pid