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
pg_stat_replication
pg_stat_wal_receiver
pg_stat_recovery_prefetch
pg_stat_subscription
pg_stat_ssl
pg_stat_gssapi
pg_stat_progress_analyze
pg_stat_progress_create_index
pg_stat_progress_vacuum
pg_stat_progress_cluster
pg_stat_progress_basebackup
pg_stat_progress_copy
Table 28.2. Collected Statistics Views
pg_stat_archiver
pg_stat_bgwriter
pg_stat_wal
pg_stat_database
pg_stat_database_conflicts
pg_stat_all_tables
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
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
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
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
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
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
pg_stat_replication_slots
pg_stat_subscription_stats
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
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
wait_event
text
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.
backend_xid
xid
Top-level transaction identifier of this backend, if any.
backend_xmin
xid
The current backend's xmin
horizon.
query_id
bigint
query
text
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
BufferPin
Client
Extension
IO
IPC
Lock
LWLock
Timeout
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
ArchiveCommand
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
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
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
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.
PgStatsDSA
Waiting for stats dynamic shared memory allocator access
PgStatsHash
Waiting for stats shared memory hash table access
PgStatsData
Waiting for shared memory stats data access
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.
Note
Extensions can add LWLock
types to the list shown in Table 28.12. 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 28.13. Wait Events of Type Timeout
Timeout
Timeout
Wait Event
Description
BaseBackupThrottle
Waiting during base backup when throttling activity.
CheckpointWriteDelay
Waiting between writes while performing a checkpoint.
PgSleep
Waiting due to a call to pg_sleep
or a sibling function.
RecoveryApplyDelay
Waiting to apply WAL during recovery because of a delay setting.
RecoveryRetrieveRetryInterval
Waiting during recovery when WAL data is not available from any source (pg_wal
, archive or stream).
RegisterSyncRequest
Waiting while sending synchronization requests to the checkpointer, because the request queue is full.
VacuumDelay
Waiting in a cost-based vacuum delay point.
VacuumTruncate
Waiting to acquire an exclusive lock to truncate off any empty pages at the end of a table vacuumed.
Here is an example of how wait events can be viewed:
28.2.4. pg_stat_replication
pg_stat_replication
The pg_stat_replication
view will contain one row per WAL sender process, showing statistics about replication to that sender's connected standby server. Only directly connected standbys are listed; no information is available about downstream standby servers.
Table 28.14. pg_stat_replication
View
pg_stat_replication
ViewColumn Type
Description
pid
integer
Process ID of a WAL sender process
usesysid
oid
OID of the user logged into this WAL sender process
usename
name
Name of the user logged into this WAL sender process
application_name
text
Name of the application that is connected to this WAL sender
client_addr
inet
IP address of the client connected to this WAL sender. If this field is null, it indicates that the client is connected via a Unix socket on the server machine.
client_hostname
text
client_port
integer
TCP port number that the client is using for communication with this WAL sender, or -1
if a Unix socket is used
backend_start
timestamp with time zone
Time when this process was started, i.e., when the client connected to this WAL sender
backend_xmin
xid
state
text
Current WAL sender state. Possible values are:
startup
: This WAL sender is starting up.catchup
: This WAL sender's connected standby is catching up with the primary.streaming
: This WAL sender is streaming changes after its connected standby server has caught up with the primary.backup
: This WAL sender is sending a backup.stopping
: This WAL sender is stopping.
sent_lsn
pg_lsn
Last write-ahead log location sent on this connection
write_lsn
pg_lsn
Last write-ahead log location written to disk by this standby server
flush_lsn
pg_lsn
Last write-ahead log location flushed to disk by this standby server
replay_lsn
pg_lsn
Last write-ahead log location replayed into the database on this standby server
write_lag
interval
Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written it (but not yet flushed it or applied it). This can be used to gauge the delay that synchronous_commit
level remote_write
incurred while committing if this server was configured as a synchronous standby.
flush_lag
interval
Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written and flushed it (but not yet applied it). This can be used to gauge the delay that synchronous_commit
level on
incurred while committing if this server was configured as a synchronous standby.
replay_lag
interval
Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. This can be used to gauge the delay that synchronous_commit
level remote_apply
incurred while committing if this server was configured as a synchronous standby.
sync_priority
integer
Priority of this standby server for being chosen as the synchronous standby in a priority-based synchronous replication. This has no effect in a quorum-based synchronous replication.
sync_state
text
Synchronous state of this standby server. Possible values are:
async
: This standby server is asynchronous.potential
: This standby server is now asynchronous, but can potentially become synchronous if one of current synchronous ones fails.sync
: This standby server is synchronous.quorum
: This standby server is considered as a candidate for quorum standbys.
reply_time
timestamp with time zone
Send time of last reply message received from standby server
The lag times reported in the pg_stat_replication
view are measurements of the time taken for recent WAL to be written, flushed and replayed and for the sender to know about it. These times represent the commit delay that was (or would have been) introduced by each synchronous commit level, if the remote server was configured as a synchronous standby. For an asynchronous standby, the replay_lag
column approximates the delay before recent transactions became visible to queries. If the standby server has entirely caught up with the sending server and there is no more WAL activity, the most recently measured lag times will continue to be displayed for a short time and then show NULL.
Lag times work automatically for physical replication. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag.
Note
The reported lag times are not predictions of how long it will take for the standby to catch up with the sending server assuming the current rate of replay. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. In particular, when the standby has caught up completely, pg_stat_replication
shows the time taken to write, flush and replay the most recent reported WAL location rather than zero as some users might expect. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. To reduce confusion for users expecting a different model of lag, the lag columns revert to NULL after a short time on a fully replayed idle system. Monitoring systems should choose whether to represent this as missing data, zero or continue to display the last known value.
28.2.5. pg_stat_replication_slots
pg_stat_replication_slots
The pg_stat_replication_slots
view will contain one row per logical replication slot, showing statistics about its usage.
Table 28.15. pg_stat_replication_slots
View
pg_stat_replication_slots
ViewColumn Type
Description
slot_name
text
A unique, cluster-wide identifier for the replication slot
spill_txns
bigint
Number of transactions spilled to disk once the memory used by logical decoding to decode changes from WAL has exceeded logical_decoding_work_mem
. The counter gets incremented for both top-level transactions and subtransactions.
spill_count
bigint
Number of times transactions were spilled to disk while decoding changes from WAL for this slot. This counter is incremented each time a transaction is spilled, and the same transaction may be spilled multiple times.
spill_bytes
bigint
Amount of decoded transaction data spilled to disk while performing decoding of changes from WAL for this slot. This and other spill counters can be used to gauge the I/O which occurred during logical decoding and allow tuning logical_decoding_work_mem
.
stream_txns
bigint
Number of in-progress transactions streamed to the decoding output plugin after the memory used by logical decoding to decode changes from WAL for this slot has exceeded logical_decoding_work_mem
. Streaming only works with top-level transactions (subtransactions can't be streamed independently), so the counter is not incremented for subtransactions.
stream_countbigint
Number of times in-progress transactions were streamed to the decoding output plugin while decoding changes from WAL for this slot. This counter is incremented each time a transaction is streamed, and the same transaction may be streamed multiple times.
stream_bytesbigint
Amount of transaction data decoded for streaming in-progress transactions to the decoding output plugin while decoding changes from WAL for this slot. This and other streaming counters for this slot can be used to tune logical_decoding_work_mem
.
total_txns
bigint
Number of decoded transactions sent to the decoding output plugin for this slot. This counts top-level transactions only, and is not incremented for subtransactions. Note that this includes the transactions that are streamed and/or spilled.
total_bytesbigint
Amount of transaction data decoded for sending transactions to the decoding output plugin while decoding changes from WAL for this slot. Note that this includes data that is streamed and/or spilled.
stats_reset
timestamp with time zone
Time at which these statistics were last reset
28.2.6. pg_stat_wal_receiver
pg_stat_wal_receiver
The pg_stat_wal_receiver
view will contain only one row, showing statistics about the WAL receiver from that receiver's connected server.
Table 28.16. pg_stat_wal_receiver
View
pg_stat_wal_receiver
ViewColumn Type
Description
pid
integer
Process ID of the WAL receiver process
status
text
Activity status of the WAL receiver process
receive_start_lsn
pg_lsn
First write-ahead log location used when WAL receiver is started
receive_start_tli
integer
First timeline number used when WAL receiver is started
written_lsn
pg_lsn
Last write-ahead log location already received and written to disk, but not flushed. This should not be used for data integrity checks.
flushed_lsn
pg_lsn
Last write-ahead log location already received and flushed to disk, the initial value of this field being the first log location used when WAL receiver is started
received_tli
integer
Timeline number of last write-ahead log location received and flushed to disk, the initial value of this field being the timeline number of the first log location used when WAL receiver is started
last_msg_send_time
timestamp with time zone
Send time of last message received from origin WAL sender
last_msg_receipt_time
timestamp with time zone
Receipt time of last message received from origin WAL sender
latest_end_lsn
pg_lsn
Last write-ahead log location reported to origin WAL sender
latest_end_time
timestamp with time zone
Time of last write-ahead log location reported to origin WAL sender
slot_name
text
Replication slot name used by this WAL receiver
sender_host
text
Host of the PostgreSQL instance this WAL receiver is connected to. This can be a host name, an IP address, or a directory path if the connection is via Unix socket. (The path case can be distinguished because it will always be an absolute path, beginning with /
.)
sender_port
integer
Port number of the PostgreSQL instance this WAL receiver is connected to.
conninfo
text
Connection string used by this WAL receiver, with security-sensitive fields obfuscated.
28.2.7. pg_stat_recovery_prefetch
pg_stat_recovery_prefetch
The pg_stat_recovery_prefetch
view will contain only one row. The columns wal_distance
, block_distance
and io_depth
show current values, and the other columns show cumulative counters that can be reset with the pg_stat_reset_shared
function.
Table 28.17. pg_stat_recovery_prefetch
View
pg_stat_recovery_prefetch
ViewColumn Type
Description
stats_reset
timestamp with time zone
Time at which these statistics were last reset
prefetch
bigint
Number of blocks prefetched because they were not in the buffer pool
hit
bigint
Number of blocks not prefetched because they were already in the buffer pool
skip_init
bigint
Number of blocks not prefetched because they would be zero-initialized
skip_new
bigint
Number of blocks not prefetched because they didn't exist yet
skip_fpw
bigint
Number of blocks not prefetched because a full page image was included in the WAL
skip_rep
bigint
Number of blocks not prefetched because they were already recently prefetched
wal_distance
int
How many bytes ahead the prefetcher is looking
block_distance
int
How many blocks ahead the prefetcher is looking
io_depth
int
How many prefetches have been initiated but are not yet known to have completed
28.2.8. pg_stat_subscription
pg_stat_subscription
Table 28.18. pg_stat_subscription
View
pg_stat_subscription
ViewColumn Type
Description
subid
oid
OID of the subscription
subname
name
Name of the subscription
pid
integer
Process ID of the subscription worker process
relid
oid
OID of the relation that the worker is synchronizing; null for the main apply worker
received_lsn
pg_lsn
Last write-ahead log location received, the initial value of this field being 0
last_msg_send_time
timestamp with time zone
Send time of last message received from origin WAL sender
last_msg_receipt_time
timestamp with time zone
Receipt time of last message received from origin WAL sender
latest_end_lsn
pg_lsn
Last write-ahead log location reported to origin WAL sender
latest_end_time
timestamp with time zone
Time of last write-ahead log location reported to origin WAL sender
28.2.9. pg_stat_subscription_stats
pg_stat_subscription_stats
The pg_stat_subscription_stats
view will contain one row per subscription.
Table 28.19. pg_stat_subscription_stats
View
pg_stat_subscription_stats
ViewColumn Type
Description
subid
oid
OID of the subscription
subname
name
Name of the subscription
apply_error_count
bigint
Number of times an error occurred while applying changes
sync_error_count
bigint
Number of times an error occurred during the initial table synchronization
stats_reset
timestamp with time zone
Time at which these statistics were last reset
28.2.10. pg_stat_ssl
pg_stat_ssl
The pg_stat_ssl
view will contain one row per backend or WAL sender process, showing statistics about SSL usage on this connection. It can be joined to pg_stat_activity
or pg_stat_replication
on the pid
column to get more details about the connection.
Table 28.20. pg_stat_ssl
View
pg_stat_ssl
ViewColumn Type
Description
pid
integer
Process ID of a backend or WAL sender process
ssl
boolean
True if SSL is used on this connection
version
text
Version of SSL in use, or NULL if SSL is not in use on this connection
cipher
text
Name of SSL cipher in use, or NULL if SSL is not in use on this connection
bits
integer
Number of bits in the encryption algorithm used, or NULL if SSL is not used on this connection
client_dn
text
Distinguished Name (DN) field from the client certificate used, or NULL if no client certificate was supplied or if SSL is not in use on this connection. This field is truncated if the DN field is longer than NAMEDATALEN
(64 characters in a standard build).
client_serial
numeric
Serial number of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. The combination of certificate serial number and certificate issuer uniquely identifies a certificate (unless the issuer erroneously reuses serial numbers).
issuer_dn
text
DN of the issuer of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. This field is truncated like client_dn
.
28.2.11. pg_stat_gssapi
pg_stat_gssapi
The pg_stat_gssapi
view will contain one row per backend, showing information about GSSAPI usage on this connection. It can be joined to pg_stat_activity
or pg_stat_replication
on the pid
column to get more details about the connection.
Table 28.21. pg_stat_gssapi
View
pg_stat_gssapi
ViewColumn Type
Description
pid
integer
Process ID of a backend
gss_authenticated
boolean
True if GSSAPI authentication was used for this connection
principal
text
Principal used to authenticate this connection, or NULL if GSSAPI was not used to authenticate this connection. This field is truncated if the principal is longer than NAMEDATALEN
(64 characters in a standard build).
encrypted
boolean
True if GSSAPI encryption is in use on this connection
28.2.12. pg_stat_archiver
pg_stat_archiver
The pg_stat_archiver
view will always have a single row, containing data about the archiver process of the cluster.
Table 28.22. pg_stat_archiver
View
pg_stat_archiver
ViewColumn Type
Description
archived_count
bigint
Number of WAL files that have been successfully archived
last_archived_wal
text
Name of the WAL file most recently successfully archived
last_archived_time
timestamp with time zone
Time of the most recent successful archive operation
failed_count
bigint
Number of failed attempts for archiving WAL files
last_failed_wal
text
Name of the WAL file of the most recent failed archival operation
last_failed_time
timestamp with time zone
Time of the most recent failed archival operation
stats_reset
timestamp with time zone
Time at which these statistics were last reset
Normally, WAL files are archived in order, oldest to newest, but that is not guaranteed, and does not hold under special circumstances like when promoting a standby or after crash recovery. Therefore it is not safe to assume that all files older than last_archived_wal
have also been successfully archived.
28.2.13. pg_stat_bgwriter
pg_stat_bgwriter
The pg_stat_bgwriter
view will always have a single row, containing global data for the cluster.
Table 28.23. pg_stat_bgwriter
View
pg_stat_bgwriter
ViewColumn Type
Description
checkpoints_timed
bigint
Number of scheduled checkpoints that have been performed
checkpoints_req
bigint
Number of requested checkpoints that have been performed
checkpoint_write_time
double precision
Total amount of time that has been spent in the portion of checkpoint processing where files are written to disk, in milliseconds
checkpoint_sync_time
double precision
Total amount of time that has been spent in the portion of checkpoint processing where files are synchronized to disk, in milliseconds
buffers_checkpoint
bigint
Number of buffers written during checkpoints
buffers_clean
bigint
Number of buffers written by the background writer
maxwritten_clean
bigint
Number of times the background writer stopped a cleaning scan because it had written too many buffers
buffers_backend
bigint
Number of buffers written directly by a backend
buffers_backend_fsync
bigint
Number of times a backend had to execute its own fsync
call (normally the background writer handles those even when the backend does its own write)
buffers_alloc
bigint
Number of buffers allocated
stats_reset
timestamp with time zone
Time at which these statistics were last reset
28.2.14. pg_stat_wal
pg_stat_wal
The pg_stat_wal
view will always have a single row, containing data about WAL activity of the cluster.
Table 28.24. pg_stat_wal
View
pg_stat_wal
ViewColumn Type
Description
wal_records
bigint
Total number of WAL records generated
wal_fpi
bigint
Total number of WAL full page images generated
wal_bytes
numeric
Total amount of WAL generated in bytes
wal_buffers_full
bigint
Number of times WAL data was written to disk because WAL buffers became full
wal_write
bigint
wal_sync
bigint
wal_write_time
double precision
wal_sync_time
double precision
Total amount of time spent syncing WAL files to disk via issue_xlog_fsync
request, in milliseconds (if track_wal_io_timing
is enabled, fsync
is on
, and wal_sync_method
is either fdatasync
, fsync
or fsync_writethrough
, otherwise zero).
stats_reset
timestamp with time zone
Time at which these statistics were last reset
28.2.15. pg_stat_database
pg_stat_database
The pg_stat_database
view will contain one row for each database in the cluster, plus one for shared objects, showing database-wide statistics.
Table 28.25. pg_stat_database
View
pg_stat_database
ViewColumn Type
Description
datid
oid
OID of this database, or 0 for objects belonging to a shared relation
datname
name
Name of this database, or NULL
for shared objects.
numbackends
integer
Number of backends currently connected to this database, or NULL
for shared objects. This is the only column in this view that returns a value reflecting current state; all other columns return the accumulated values since the last reset.
xact_commit
bigint
Number of transactions in this database that have been committed
xact_rollback
bigint
Number of transactions in this database that have been rolled back
blks_read
bigint
Number of disk blocks read in this database
blks_hit
bigint
Number of times disk blocks were found already in the buffer cache, so that a read was not necessary (this only includes hits in the PostgreSQL buffer cache, not the operating system's file system cache)
tup_returned
bigint
Number of live rows fetched by sequential scans and index entries returned by index scans in this database
tup_fetched
bigint
Number of live rows fetched by index scans in this database
tup_inserted
bigint
Number of rows inserted by queries in this database
tup_updated
bigint
Number of rows updated by queries in this database
tup_deleted
bigint
Number of rows deleted by queries in this database
conflicts
bigint
temp_files
bigint
temp_bytes
bigint
deadlocks
bigint
Number of deadlocks detected in this database
checksum_failures
bigint
Number of data page checksum failures detected in this database (or on a shared object), or NULL if data checksums are not enabled.
checksum_last_failure
timestamp with time zone
Time at which the last data page checksum failure was detected in this database (or on a shared object), or NULL if data checksums are not enabled.
blk_read_time
double precision
blk_write_time
double precision
session_time
double precision
Time spent by database sessions in this database, in milliseconds (note that statistics are only updated when the state of a session changes, so if sessions have been idle for a long time, this idle time won't be included)
active_time
double precision
idle_in_transaction_time
double precision
sessions
bigint
Total number of sessions established to this database
sessions_abandoned
bigint
Number of database sessions to this database that were terminated because connection to the client was lost
sessions_fatal
bigint
Number of database sessions to this database that were terminated by fatal errors
sessions_killed
bigint
Number of database sessions to this database that were terminated by operator intervention
stats_reset
timestamp with time zone
Time at which these statistics were last reset
28.2.16. pg_stat_database_conflicts
pg_stat_database_conflicts
The pg_stat_database_conflicts
view will contain one row per database, showing database-wide statistics about query cancels occurring due to conflicts with recovery on standby servers. This view will only contain information on standby servers, since conflicts do not occur on primary servers.
Table 28.26. pg_stat_database_conflicts
View
pg_stat_database_conflicts
ViewColumn Type
Description
datid
oid
OID of a database
datname
name
Name of this database
confl_tablespace
bigint
Number of queries in this database that have been canceled due to dropped tablespaces
confl_lock
bigint
Number of queries in this database that have been canceled due to lock timeouts
confl_snapshot
bigint
Number of queries in this database that have been canceled due to old snapshots
confl_bufferpin
bigint
Number of queries in this database that have been canceled due to pinned buffers
confl_deadlock
bigint
Number of queries in this database that have been canceled due to deadlocks
28.2.17. pg_stat_all_tables
pg_stat_all_tables
The pg_stat_all_tables
view will contain one row for each table in the current database (including TOAST tables), showing statistics about accesses to that specific table. The pg_stat_user_tables
and pg_stat_sys_tables
views contain the same information, but filtered to only show user and system tables respectively.
Table 28.27. pg_stat_all_tables
View
pg_stat_all_tables
ViewColumn Type
Description
relid
oid
OID of a table
schemaname
name
Name of the schema that this table is in
relname
name
Name of this table
seq_scan
bigint
Number of sequential scans initiated on this table
seq_tup_read
bigint
Number of live rows fetched by sequential scans
idx_scan
bigint
Number of index scans initiated on this table
idx_tup_fetch
bigint
Number of live rows fetched by index scans
n_tup_ins
bigint
Number of rows inserted
n_tup_upd
bigint
n_tup_del
bigint
Number of rows deleted
n_tup_hot_upd
bigint
Number of rows HOT updated (i.e., with no separate index update required)
n_live_tup
bigint
Estimated number of live rows
n_dead_tup
bigint
Estimated number of dead rows
n_mod_since_analyze
bigint
Estimated number of rows modified since this table was last analyzed
n_ins_since_vacuum
bigint
Estimated number of rows inserted since this table was last vacuumed
last_vacuum
timestamp with time zone
Last time at which this table was manually vacuumed (not counting VACUUM FULL
)
last_autovacuum
timestamp with time zone
Last time at which this table was vacuumed by the autovacuum daemon
last_analyze
timestamp with time zone
Last time at which this table was manually analyzed
last_autoanalyze
timestamp with time zone
Last time at which this table was analyzed by the autovacuum daemon
vacuum_count
bigint
Number of times this table has been manually vacuumed (not counting VACUUM FULL
)
autovacuum_count
bigint
Number of times this table has been vacuumed by the autovacuum daemon
analyze_count
bigint
Number of times this table has been manually analyzed
autoanalyze_count
bigint
Number of times this table has been analyzed by the autovacuum daemon
28.2.18. pg_stat_all_indexes
pg_stat_all_indexes
The pg_stat_all_indexes
view will contain one row for each index in the current database, showing statistics about accesses to that specific index. The pg_stat_user_indexes
and pg_stat_sys_indexes
views contain the same information, but filtered to only show user and system indexes respectively.
Table 28.28. pg_stat_all_indexes
View
pg_stat_all_indexes
ViewColumn Type
Description
relid
oid
OID of the table for this index
indexrelid
oid
OID of this index
schemaname
name
Name of the schema this index is in
relname
name
Name of the table for this index
indexrelname
name
Name of this index
idx_scan
bigint
Number of index scans initiated on this index
idx_tup_read
bigint
Number of index entries returned by scans on this index
idx_tup_fetch
bigint
Number of live table rows fetched by simple index scans using this index
Indexes can be used by simple index scans, “bitmap” index scans, and the optimizer. In a bitmap scan the output of several indexes can be combined via AND or OR rules, so it is difficult to associate individual heap row fetches with specific indexes when a bitmap scan is used. Therefore, a bitmap scan increments the pg_stat_all_indexes
.idx_tup_read
count(s) for the index(es) it uses, and it increments the pg_stat_all_tables
.idx_tup_fetch
count for the table, but it does not affect pg_stat_all_indexes
.idx_tup_fetch
. The optimizer also accesses indexes to check for supplied constants whose values are outside the recorded range of the optimizer statistics because the optimizer statistics might be stale.
Note
The idx_tup_read
and idx_tup_fetch
counts can be different even without any use of bitmap scans, because idx_tup_read
counts index entries retrieved from the index while idx_tup_fetch
counts live rows fetched from the table. The latter will be less if any dead or not-yet-committed rows are fetched using the index, or if any heap fetches are avoided by means of an index-only scan.
28.2.19. pg_statio_all_tables
pg_statio_all_tables
The pg_statio_all_tables
view will contain one row for each table in the current database (including TOAST tables), showing statistics about I/O on that specific table. The pg_statio_user_tables
and pg_statio_sys_tables
views contain the same information, but filtered to only show user and system tables respectively.
Table 28.29. pg_statio_all_tables
View
pg_statio_all_tables
ViewColumn Type
Description
relid
oid
OID of a table
schemaname
name
Name of the schema that this table is in
relname
name
Name of this table
heap_blks_read
bigint
Number of disk blocks read from this table
heap_blks_hit
bigint
Number of buffer hits in this table
idx_blks_read
bigint
Number of disk blocks read from all indexes on this table
idx_blks_hit
bigint
Number of buffer hits in all indexes on this table
toast_blks_read
bigint
Number of disk blocks read from this table's TOAST table (if any)
toast_blks_hit
bigint
Number of buffer hits in this table's TOAST table (if any)
tidx_blks_read
bigint
Number of disk blocks read from this table's TOAST table indexes (if any)
tidx_blks_hit
bigint
Number of buffer hits in this table's TOAST table indexes (if any)
28.2.20. pg_statio_all_indexes
pg_statio_all_indexes
The pg_statio_all_indexes
view will contain one row for each index in the current database, showing statistics about I/O on that specific index. The pg_statio_user_indexes
and pg_statio_sys_indexes
views contain the same information, but filtered to only show user and system indexes respectively.
Table 28.30. pg_statio_all_indexes
View
pg_statio_all_indexes
ViewColumn Type
Description
relid
oid
OID of the table for this index
indexrelid
oid
OID of this index
schemaname
name
Name of the schema this index is in
relname
name
Name of the table for this index
indexrelname
name
Name of this index
idx_blks_read
bigint
Number of disk blocks read from this index
idx_blks_hit
bigint
Number of buffer hits in this index
28.2.21. pg_statio_all_sequences
pg_statio_all_sequences
The pg_statio_all_sequences
view will contain one row for each sequence in the current database, showing statistics about I/O on that specific sequence.
Table 28.31. pg_statio_all_sequences
View
pg_statio_all_sequences
ViewColumn Type
Description
relid
oid
OID of a sequence
schemaname
name
Name of the schema this sequence is in
relname
name
Name of this sequence
blks_read
bigint
Number of disk blocks read from this sequence
blks_hit
bigint
Number of buffer hits in this sequence
28.2.22. pg_stat_user_functions
pg_stat_user_functions
The pg_stat_user_functions
view will contain one row for each tracked function, showing statistics about executions of that function. The track_functions parameter controls exactly which functions are tracked.
Table 28.32. pg_stat_user_functions
View
pg_stat_user_functions
ViewColumn Type
Description
funcid
oid
OID of a function
schemaname
name
Name of the schema this function is in
funcname
name
Name of this function
calls
bigint
Number of times this function has been called
total_time
double precision
Total time spent in this function and all other functions called by it, in milliseconds
self_time
double precision
Total time spent in this function itself, not including other functions called by it, in milliseconds
28.2.23. pg_stat_slru
pg_stat_slru
PostgreSQL accesses certain on-disk information via SLRU (simple least-recently-used) caches. The pg_stat_slru
view will contain one row for each tracked SLRU cache, showing statistics about access to cached pages.
Table 28.33. pg_stat_slru
View
pg_stat_slru
ViewColumn Type
Description
name
text
Name of the SLRU
blks_zeroed
bigint
Number of blocks zeroed during initializations
blks_hit
bigint
Number of times disk blocks were found already in the SLRU, so that a read was not necessary (this only includes hits in the SLRU, not the operating system's file system cache)
blks_read
bigint
Number of disk blocks read for this SLRU
blks_written
bigint
Number of disk blocks written for this SLRU
blks_exists
bigint
Number of blocks checked for existence for this SLRU
flushes
bigint
Number of flushes of dirty data for this SLRU
truncates
bigint
Number of truncates for this SLRU
stats_reset
timestamp with time zone
Time at which these statistics were last reset
28.2.24. Statistics Functions
Other ways of looking at the statistics can be set up by writing queries that use the same underlying statistics access functions used by the standard views shown above. For details such as the functions' names, consult the definitions of the standard views. (For example, in psql you could issue \d+ pg_stat_activity
.) The access functions for per-database statistics take a database OID as an argument to identify which database to report on. The per-table and per-index functions take a table or index OID. The functions for per-function statistics take a function OID. Note that only tables, indexes, and functions in the current database can be seen with these functions.
Additional functions related to the cumulative statistics system are listed in Table 28.34.
Table 28.34. Additional Statistics Functions
Function
Description
pg_backend_pid
() → integer
Returns the process ID of the server process attached to the current session.
pg_stat_get_activity
( integer
) → setof record
Returns a record of information about the backend with the specified process ID, or one record for each active backend in the system if NULL
is specified. The fields returned are a subset of those in the pg_stat_activity
view.
pg_stat_get_snapshot_timestamp
() → timestamp with time zone
Returns the timestamp of the current statistics snapshot, or NULL if no statistics snapshot has been taken. A snapshot is taken the first time cumulative statistics are accessed in a transaction if stats_fetch_consistency
is set to snapshot
pg_stat_clear_snapshot
() → void
Discards the current statistics snapshot or cached information.
pg_stat_reset
() → void
Resets all statistics counters for the current database to zero.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_stat_reset_shared
( text
) → void
Resets some cluster-wide statistics counters to zero, depending on the argument. The argument can be bgwriter
to reset all the counters shown in the pg_stat_bgwriter
view, archiver
to reset all the counters shown in the pg_stat_archiver
view, wal
to reset all the counters shown in the pg_stat_wal
view or recovery_prefetch
to reset all the counters shown in the pg_stat_recovery_prefetch
view.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_stat_reset_single_table_counters
( oid
) → void
Resets statistics for a single table or index in the current database or shared across all databases in the cluster to zero.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_stat_reset_single_function_counters
( oid
) → void
Resets statistics for a single function in the current database to zero.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_stat_reset_slru
( text
) → void
Resets statistics to zero for a single SLRU cache, or for all SLRUs in the cluster. If the argument is NULL, all counters shown in the pg_stat_slru
view for all SLRU caches are reset. The argument can be one of CommitTs
, MultiXactMember
, MultiXactOffset
, Notify
, Serial
, Subtrans
, or Xact
to reset the counters for only that entry. If the argument is other
(or indeed, any unrecognized name), then the counters for all other SLRU caches, such as extension-defined caches, are reset.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_stat_reset_replication_slot
( text
) → void
Resets statistics of the replication slot defined by the argument. If the argument is NULL
, resets statistics for all the replication slots.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_stat_reset_subscription_stats
( oid
) → void
Resets statistics for a single subscription shown in the pg_stat_subscription_stats
view to zero. If the argument is NULL
, reset statistics for all subscriptions.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
Warning
Using pg_stat_reset()
also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Resetting these counters can cause autovacuum to not perform necessary work, which can cause problems such as table bloat or out-dated table statistics. A database-wide ANALYZE
is recommended after the statistics have been reset.
pg_stat_get_activity
, the underlying function of the pg_stat_activity
view, returns a set of records containing all the available information about each backend process. Sometimes it may be more convenient to obtain just a subset of this information. In such cases, an older set of per-backend statistics access functions can be used; these are shown in Table 28.35. These access functions use a backend ID number, which ranges from one to the number of currently active backends. The function pg_stat_get_backend_idset
provides a convenient way to generate one row for each active backend for invoking these functions. For example, to show the PIDs and current queries of all backends:
Table 28.35. Per-Backend Statistics Functions
Function
Description
pg_stat_get_backend_idset
() → setof integer
Returns the set of currently active backend ID numbers (from 1 to the number of active backends).
pg_stat_get_backend_activity
( integer
) → text
Returns the text of this backend's most recent query.
pg_stat_get_backend_activity_start
( integer
) → timestamp with time zone
Returns the time when the backend's most recent query was started.
pg_stat_get_backend_client_addr
( integer
) → inet
Returns the IP address of the client connected to this backend.
pg_stat_get_backend_client_port
( integer
) → integer
Returns the TCP port number that the client is using for communication.
pg_stat_get_backend_dbid
( integer
) → oid
Returns the OID of the database this backend is connected to.
pg_stat_get_backend_pid
( integer
) → integer
Returns the process ID of this backend.
pg_stat_get_backend_start
( integer
) → timestamp with time zone
Returns the time when this process was started.
pg_stat_get_backend_userid
( integer
) → oid
Returns the OID of the user logged into this backend.
pg_stat_get_backend_wait_event_type
( integer
) → text
pg_stat_get_backend_wait_event
( integer
) → text
pg_stat_get_backend_xact_start
( integer
) → timestamp with time zone
Returns the time when the backend's current transaction was started.