aurora_stat_backend_waits - Amazon Aurora

aurora_stat_backend_waits

Displays statistics for wait activity for a specific backend process.

Syntax

aurora_stat_backend_waits(pid)

Arguments

pid – The ID for the backend process. You can obtain process IDs by using the pg_stat_activity view.

Return type

SETOF record with following columns:

  • type_id – A number that denotes the type of wait event, such as 1 for a lightweight lock (LWLock), 3 for a lock, or 6 for a client session, to name some examples. These values become meaningful when you join the results of this function with columns from aurora_stat_wait_type function, as shown in the Examples.

  • event_id – An identifying number for the wait event. Join this value with the columns from aurora_stat_wait_event to obtain meaningful event names.

  • waits – A count of the number of waits accumulated for the specified process ID.

  • wait_time – Wait time in milliseconds.

Usage notes

You can use this function to analyze specific backend (session) wait events that occurred since a connection opened. To get more meaningful information about wait event names and types, you can combine this function aurora_stat_wait_type and aurora_stat_wait_event, by using JOIN as shown in the examples.

Examples

This example shows all waits, types, and event names for a backend process ID 3027.

=> SELECT type_name, event_name, waits, wait_time FROM aurora_stat_backend_waits(3027) NATURAL JOIN aurora_stat_wait_type() NATURAL JOIN aurora_stat_wait_event(); type_name | event_name | waits | wait_time -----------+------------------------+-------+------------ LWLock | ProcArrayLock | 3 | 27 LWLock | wal_insert | 423 | 16336 LWLock | buffer_content | 11840 | 1033634 LWLock | lock_manager | 23821 | 5664506 Lock | tuple | 10258 | 152280165 Lock | transactionid | 78340 | 1239808783 Client | ClientRead | 34072 | 17616684 IO | ControlFileSyncUpdate | 2 | 0 IO | ControlFileWriteUpdate | 4 | 32 IO | RelationMapRead | 2 | 795 IO | WALWrite | 36666 | 98623 IO | XactSync | 4867 | 7331963

This example shows current and cumulative wait types and wait events for all active sessions (pg_stat_activity state <> 'idle') (but without the current session that's invoking the function (pid <> pg_backend_pid()).

=> SELECT a.pid, a.usename, a.app_name, a.current_wait_type, a.current_wait_event, a.current_state, wt.type_name AS wait_type, we.event_name AS wait_event, a.waits, a.wait_time FROM (SELECT pid, usename, left(application_name,16) AS app_name, coalesce(wait_event_type,'CPU') AS current_wait_type, coalesce(wait_event,'CPU') AS current_wait_event, state AS current_state, (aurora_stat_backend_waits(pid)).* FROM pg_stat_activity WHERE pid <> pg_backend_pid() AND state <> 'idle') a NATURAL JOIN aurora_stat_wait_type() wt NATURAL JOIN aurora_stat_wait_event() we; pid | usename | app_name | current_wait_type | current_wait_event | current_state | wait_type | wait_event | waits | wait_time -------+----------+----------+-------------------+--------------------+---------------+-----------+------------------------+-------+----------- 30099 | postgres | pgbench | Lock | transactionid | active | LWLock | wal_insert | 1937 | 29975 30099 | postgres | pgbench | Lock | transactionid | active | LWLock | buffer_content | 22903 | 760498 30099 | postgres | pgbench | Lock | transactionid | active | LWLock | lock_manager | 10012 | 223207 30099 | postgres | pgbench | Lock | transactionid | active | Lock | tuple | 20315 | 63081529 . . . 30099 | postgres | pgbench | Lock | transactionid | active | IO | WALWrite | 93293 | 237440 30099 | postgres | pgbench | Lock | transactionid | active | IO | XactSync | 13010 | 19525143 30100 | postgres | pgbench | Lock | transactionid | active | LWLock | ProcArrayLock | 6 | 53 30100 | postgres | pgbench | Lock | transactionid | active | LWLock | wal_insert | 1913 | 25450 30100 | postgres | pgbench | Lock | transactionid | active | LWLock | buffer_content | 22874 | 778005 . . . 30109 | postgres | pgbench | IO | XactSync | active | LWLock | ProcArrayLock | 3 | 71 30109 | postgres | pgbench | IO | XactSync | active | LWLock | wal_insert | 1940 | 27741 30109 | postgres | pgbench | IO | XactSync | active | LWLock | buffer_content | 22962 | 776352 30109 | postgres | pgbench | IO | XactSync | active | LWLock | lock_manager | 9879 | 218826 30109 | postgres | pgbench | IO | XactSync | active | Lock | tuple | 20401 | 63581306 30109 | postgres | pgbench | IO | XactSync | active | Lock | transactionid | 50769 | 211645008 30109 | postgres | pgbench | IO | XactSync | active | Client | ClientRead | 89901 | 44192439

This example shows current and the top three (3) cumulative wait type and wait events for all active sessions (pg_stat_activity state <> 'idle') excluding current session (pid <>pg_backend_pid()).

=> SELECT top3.* FROM (SELECT a.pid, a.usename, a.app_name, a.current_wait_type, a.current_wait_event, a.current_state, wt.type_name AS wait_type, we.event_name AS wait_event, a.waits, a.wait_time, RANK() OVER (PARTITION BY pid ORDER BY a.wait_time DESC) FROM (SELECT pid, usename, left(application_name,16) AS app_name, coalesce(wait_event_type,'CPU') AS current_wait_type, coalesce(wait_event,'CPU') AS current_wait_event, state AS current_state, (aurora_stat_backend_waits(pid)).* FROM pg_stat_activity WHERE pid <> pg_backend_pid() AND state <> 'idle') a NATURAL JOIN aurora_stat_wait_type() wt NATURAL JOIN aurora_stat_wait_event() we) top3 WHERE RANK <=3; pid | usename | app_name | current_wait_type | current_wait_event | current_state | wait_type | wait_event | waits | wait_time | rank -------+----------+----------+-------------------+--------------------+---------------+-----------+-----------------+---------+------------+------ 20567 | postgres | psql | CPU | CPU | active | LWLock | wal_insert | 25000 | 67512003 | 1 20567 | postgres | psql | CPU | CPU | active | IO | WALWrite | 3071758 | 1016961 | 2 20567 | postgres | psql | CPU | CPU | active | IO | BufFileWrite | 20750 | 184559 | 3 27743 | postgres | pgbench | Lock | transactionid | active | Lock | transactionid | 237350 | 1265580011 | 1 27743 | postgres | pgbench | Lock | transactionid | active | Lock | tuple | 93641 | 341472318 | 2 27743 | postgres | pgbench | Lock | transactionid | active | Client | ClientRead | 417556 | 204796837 | 3 . . . 27745 | postgres | pgbench | IO | XactSync | active | Lock | transactionid | 238068 | 1265816822 | 1 27745 | postgres | pgbench | IO | XactSync | active | Lock | tuple | 93210 | 338312247 | 2 27745 | postgres | pgbench | IO | XactSync | active | Client | ClientRead | 419157 | 207836533 | 3 27746 | postgres | pgbench | Lock | transactionid | active | Lock | transactionid | 237621 | 1264528811 | 1 27746 | postgres | pgbench | Lock | transactionid | active | Lock | tuple | 93563 | 339799310 | 2 27746 | postgres | pgbench | Lock | transactionid | active | Client | ClientRead | 417304 | 208372727 | 3