Monitoring Stats – ProtonBase 文档

The Statistics Collector

ProtonBase's statistics collector is a subsystem that supports collection and reporting of information about server activity. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. It also tracks the total number of rows in each table, and information about vacuum and analyze actions for each table. It can also count calls to user-defined functions and the total time spent in each one.

ProtonBase 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 collector process.

Viewing Statistics

Several predefined views, listed in Table 11.1, are available to show the current state of the system. There are also several other views, listed in "monitoring-stats-views-table", available to show the results of statistics collection. Alternatively, one can build custom views using the underlying statistics functions, as discussed in "monitoring-stats-functions".

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 11.1 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 can see all the information about all sessions.

Table 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_activity`

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

Table pg_stat_activity View

Column Type Description

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. `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 "guc-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 11.3.
`wait_event` `text` Wait event name if backend is currently waiting, otherwise NULL. See Table 11.4 through Table 11.12.
`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 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 "guc-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 "guc-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 "guc-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.

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 "guc-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 11.3.

wait_event text

Wait event name if backend is currently waiting, otherwise NULL. See Table 11.4 through Table 11.12.

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 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 "guc-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 "guc-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 "guc-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.

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 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 11.4.
`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 11.5.
`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 11.6.
`Extension`	The server process is waiting for some condition defined by an extension module. See Table 11.7.
`IO`	The server process is waiting for an I/O operation to complete. `wait_event` will identify the specific wait point; see Table 11.8.
`IPC`	The server process is waiting for some interaction with another server process. `wait_event` will identify the specific wait point; see Table 11.9.
`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 11.10.
`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 11.11.
`Timeout`	The server process is waiting for a timeout to expire. `wait_event` will identify the specific wait point; see Table 11.12.

Table 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.
`LogicalApplyMain`	Waiting in main loop of logical replication apply process.
`LogicalLauncherMain`	Waiting in main loop of logical replication launcher process.
`PgStatMain`	Waiting in main loop of statistics collector 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 Wait Events of Type BufferPin

`BufferPin` Wait Event	Description
`BufferPin`	Waiting to acquire an exclusive pin on a buffer.

Table 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.
`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 Wait Events of Type Extension

`Extension` Wait Event	Description
`Extension`	Waiting in an extension.

Table Wait Events of Type 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.
`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.
`LogicalChangesRead`	Waiting for a read from a logical changes file.
`LogicalChangesWrite`	Waiting for a write to a logical changes file.
`LogicalSubxactRead`	Waiting for a read from a logical subxact file.
`LogicalSubxactWrite`	Waiting for a write to a logical subxact file.

Table Wait Events of Type IPC

`IPC` Wait Event	Description
`AppendReady`	Waiting for subplan nodes of an `Append` plan node to be ready.
`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.
`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.
`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 Wait Events of Type 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 Wait Events of Type 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`	Waiting to read or update the last value set for a transaction commit timestamp.
`CommitTsBuffer`	Waiting for I/O on a commit timestamp SLRU buffer.
`CommitTsSLRU`	Waiting to access the commit timestamp SLRU cache.
`ControlFile`	Waiting to read or update the `pg_control` file or create a new WAL file.
`DynamicSharedMemoryControl`	Waiting to read or update dynamic shared memory allocation information.
`LockFastPath`	Waiting to read or update a process' fast-path lock information.
`LockManager`	Waiting to read or update information about “heavyweight” locks.
`LogicalRepWorker`	Waiting to read or update the state of logical replication workers.
`MultiXactGen`	Waiting to read or update shared multixact state.
`MultiXactMemberBuffer`	Waiting for I/O on a multixact member SLRU buffer.
`MultiXactMemberSLRU`	Waiting to access the multixact member SLRU cache.
`MultiXactOffsetBuffer`	Waiting for I/O on a multixact offset SLRU buffer.
`MultiXactOffsetSLRU`	Waiting to access the multixact offset SLRU cache.
`MultiXactTruncation`	Waiting to read or truncate multixact information.
`NotifyBuffer`	Waiting for I/O on a `NOTIFY` message SLRU buffer.
`NotifyQueue`	Waiting to read or update `NOTIFY` messages.
`NotifyQueueTail`	Waiting to update limit on `NOTIFY` message storage.
`NotifySLRU`	Waiting to access the `NOTIFY` message SLRU cache.
`OidGen`	Waiting to allocate a new OID.
`OldSnapshotTimeMap`	Waiting to read or update old snapshot control information.
`ParallelAppend`	Waiting to choose the next subplan during Parallel Append plan execution.
`ParallelHashJoin`	Waiting to synchronize workers during Parallel Hash Join plan execution.
`ParallelQueryDSA`	Waiting for parallel query dynamic shared memory allocation.
`PerSessionDSA`	Waiting for parallel query dynamic shared memory allocation.
`PerSessionRecordType`	Waiting to access a parallel query's information about composite types.
`PerSessionRecordTypmod`	Waiting to access a parallel query's information about type modifiers that identify anonymous record types.
`PerXactPredicateList`	Waiting to access the list of predicate locks held by the current serializable transaction during a parallel query.
`PredicateLockManager`	Waiting to access predicate lock information used by serializable transactions.
`ProcArray`	Waiting to access the shared per-process data structures (typically, to get a snapshot or report a session's transaction ID).
`RelationMapping`	Waiting to read or update a `pg_filenode.map` file (used to track the filenode assignments of certain system catalogs).
`RelCacheInit`	Waiting to read or update a `pg_internal.init` relation cache initialization file.
`ReplicationOrigin`	Waiting to create, drop or use a replication origin.
`ReplicationOriginState`	Waiting to read or update the progress of one replication origin.
`ReplicationSlotAllocation`	Waiting to allocate or free a replication slot.
`ReplicationSlotControl`	Waiting to read or update replication slot state.
`ReplicationSlotIO`	Waiting for I/O on a replication slot.
`SerialBuffer`	Waiting for I/O on a serializable transaction conflict SLRU buffer.
`SerializableFinishedList`	Waiting to access the list of finished serializable transactions.
`SerializablePredicateList`	Waiting to access the list of predicate locks held by serializable transactions.
`SerializableXactHash`	Waiting to read or update information about serializable transactions.
`SerialSLRU`	Waiting to access the serializable transaction conflict SLRU cache.
`SharedTidBitmap`	Waiting to access a shared TID bitmap during a parallel bitmap index scan.
`SharedTupleStore`	Waiting to access a shared tuple store during parallel query.
`ShmemIndex`	Waiting to find or allocate space in shared memory.
`SInvalRead`	Waiting to retrieve messages from the shared catalog invalidation queue.
`SInvalWrite`	Waiting to add a message to the shared catalog invalidation queue.
`SubtransBuffer`	Waiting for I/O on a sub-transaction SLRU buffer.
`SubtransSLRU`	Waiting to access the sub-transaction SLRU cache.
`SyncRep`	Waiting to read or update information about the state of synchronous replication.
`SyncScan`	Waiting to select the starting location of a synchronized table scan.
`TablespaceCreate`	Waiting to create or drop a tablespace.
`TwoPhaseState`	Waiting to read or update the state of prepared transactions.
`WALBufMapping`	Waiting to replace a page in WAL buffers.
`WALInsert`	Waiting to insert WAL data into a memory buffer.
`WALWrite`	Waiting for WAL buffers to be written to disk.
`WrapLimitsVacuum`	Waiting to update limits on transaction id and multixact consumption.
`XactBuffer`	Waiting for I/O on a transaction status SLRU buffer.
`XactSLRU`	Waiting to access the transaction status SLRU cache.
`XactTruncation`	Waiting to execute `pg_xact_status` or update the oldest transaction ID available to it.
`XidGen`	Waiting to allocate a new transaction ID.

Extensions can add LWLock types to the list shown in Table 11.11. In some cases, the name assigned by an extension will not be available in all server processes; so an LWLock wait event might be reported as just “extension” rather than the extension-assigned name.

Table Wait Events of Type Timeout

`Timeout` Wait Event	Description
`BaseBackupThrottle`	Waiting during base backup when throttling activity.
`PgSleep`	Waiting due to a call to `pg_sleep` or a sibling function.
`RecoveryApplyDelay`	Waiting to apply WAL during recovery because of a delay setting.
`RecoveryRetrieveRetryInterval`	Waiting during recovery when WAL data is not available from any source (`pg_wal`, archive or stream).
`VacuumDelay`	Waiting in a cost-based vacuum delay point.

Here is an example of how wait events can be viewed:

SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event is NOT NULL;
pid  | wait_event_type | wait_event
------+----------------+------------
2540 | Lock            | relation
6644 | LWLock          | ProcArray
(2 rows)