From 10ea0f924a2788f9e701d6213745aaa5ca3efb8a Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Mon, 19 Dec 2022 14:43:09 -0500 Subject: [PATCH] Expose some information about backend subxact status. A new function pg_stat_get_backend_subxact() can be used to get information about the number of subtransactions in the cache of a particular backend and whether that cache has overflowed. This can be useful for tracking down performance problems that can result from overflowed snapshots. Dilip Kumar, reviewed by Zhihong Yu, Nikolay Samokhvalov, Justin Pryzby, Nathan Bossart, Ashutosh Sharma, Julien Rouhaud. Additional design comments from Andres Freund, Tom Lane, Bruce Momjian, and David G. Johnston. Discussion: http://postgr.es/m/CAFiTN-ut0uwkRJDQJeDPXpVyTWD46m3gt3JDToE02hTfONEN=Q@mail.gmail.com --- doc/src/sgml/monitoring.sgml | 18 ++++++++++ src/backend/storage/ipc/sinvaladt.c | 13 ++++--- src/backend/utils/activity/backend_status.c | 4 ++- src/backend/utils/adt/pgstatfuncs.c | 38 +++++++++++++++++++++ src/include/catalog/catversion.h | 2 +- src/include/catalog/pg_proc.dat | 7 ++++ src/include/storage/sinvaladt.h | 4 ++- src/include/utils/backend_status.h | 11 ++++++ 8 files changed, 90 insertions(+), 7 deletions(-) diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index 11a8ebe5ec..363b183e5f 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -5671,6 +5671,24 @@ FROM pg_stat_get_backend_idset() AS backendid; + + + + pg_stat_get_backend_subxact + + pg_stat_get_backend_subxact ( integer ) + record + + + Returns a record of information about the subtransactions of the + backend with the specified ID. + The fields returned are subxact_count, which + is the number of subtransactions in the backend's subtransaction cache, + and subxact_overflow, which indicates whether + the backend's subtransaction cache is overflowed or not. + + + diff --git a/src/backend/storage/ipc/sinvaladt.c b/src/backend/storage/ipc/sinvaladt.c index 59310b708f..4a20fe7ebe 100644 --- a/src/backend/storage/ipc/sinvaladt.c +++ b/src/backend/storage/ipc/sinvaladt.c @@ -404,17 +404,20 @@ BackendIdGetProc(int backendID) /* * BackendIdGetTransactionIds - * Get the xid and xmin of the backend. The result may be out of date - * arbitrarily quickly, so the caller must be careful about how this - * information is used. + * Get the xid, xmin, nsubxid and overflow status of the backend. The + * result may be out of date arbitrarily quickly, so the caller must be + * careful about how this information is used. */ void -BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmin) +BackendIdGetTransactionIds(int backendID, TransactionId *xid, + TransactionId *xmin, int *nsubxid, bool *overflowed) { SISeg *segP = shmInvalBuffer; *xid = InvalidTransactionId; *xmin = InvalidTransactionId; + *nsubxid = 0; + *overflowed = false; /* Need to lock out additions/removals of backends */ LWLockAcquire(SInvalWriteLock, LW_SHARED); @@ -428,6 +431,8 @@ BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmi { *xid = proc->xid; *xmin = proc->xmin; + *nsubxid = proc->subxidStatus.count; + *overflowed = proc->subxidStatus.overflowed; } } diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c index 1146a6c33c..7ecf467b8c 100644 --- a/src/backend/utils/activity/backend_status.c +++ b/src/backend/utils/activity/backend_status.c @@ -855,7 +855,9 @@ pgstat_read_current_status(void) localentry->backend_id = i; BackendIdGetTransactionIds(i, &localentry->backend_xid, - &localentry->backend_xmin); + &localentry->backend_xmin, + &localentry->backend_subxact_count, + &localentry->backend_subxact_overflowed); localentry++; localappname += NAMEDATALEN; diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c index 04a5a99002..46f98fd67f 100644 --- a/src/backend/utils/adt/pgstatfuncs.c +++ b/src/backend/utils/adt/pgstatfuncs.c @@ -687,6 +687,44 @@ pg_stat_get_backend_userid(PG_FUNCTION_ARGS) PG_RETURN_OID(beentry->st_userid); } +Datum +pg_stat_get_backend_subxact(PG_FUNCTION_ARGS) +{ +#define PG_STAT_GET_SUBXACT_COLS 2 + TupleDesc tupdesc; + Datum values[PG_STAT_GET_SUBXACT_COLS]; + bool nulls[PG_STAT_GET_SUBXACT_COLS]; + int32 beid = PG_GETARG_INT32(0); + LocalPgBackendStatus *local_beentry; + + /* Initialise values and NULL flags arrays */ + MemSet(values, 0, sizeof(values)); + MemSet(nulls, 0, sizeof(nulls)); + + /* Initialise attributes information in the tuple descriptor */ + tupdesc = CreateTemplateTupleDesc(PG_STAT_GET_SUBXACT_COLS); + TupleDescInitEntry(tupdesc, (AttrNumber) 1, "subxact_count", + INT4OID, -1, 0); + TupleDescInitEntry(tupdesc, (AttrNumber) 2, "subxact_overflow", + BOOLOID, -1, 0); + + BlessTupleDesc(tupdesc); + + if ((local_beentry = pgstat_fetch_stat_local_beentry(beid)) != NULL) + { + /* Fill values and NULLs */ + values[0] = Int32GetDatum(local_beentry->backend_subxact_count); + values[1] = BoolGetDatum(local_beentry->backend_subxact_overflowed); + } + else + { + nulls[0] = true; + nulls[1] = true; + } + + /* Returns the record as Datum */ + PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls))); +} Datum pg_stat_get_backend_activity(PG_FUNCTION_ARGS) diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h index 5cb12437a6..094f59f82d 100644 --- a/src/include/catalog/catversion.h +++ b/src/include/catalog/catversion.h @@ -57,6 +57,6 @@ */ /* yyyymmddN */ -#define CATALOG_VERSION_NO 202212131 +#define CATALOG_VERSION_NO 202212191 #endif diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat index 719599649a..d763419c0d 100644 --- a/src/include/catalog/pg_proc.dat +++ b/src/include/catalog/pg_proc.dat @@ -5441,6 +5441,13 @@ proname => 'pg_stat_get_backend_dbid', provolatile => 's', proparallel => 'r', prorettype => 'oid', proargtypes => 'int4', prosrc => 'pg_stat_get_backend_dbid' }, +{ oid => '6107', descr => 'statistics: get subtransaction status of backend', + proname => 'pg_stat_get_backend_subxact', provolatile => 's', proparallel => 'r', + prorettype => 'record', proargtypes => 'int4', + proallargtypes => '{int4,int4,bool}', + proargmodes => '{i,o,o}', + proargnames => '{bid,subxact_count,subxact_overflowed}', + prosrc => 'pg_stat_get_backend_subxact' }, { oid => '1939', descr => 'statistics: user ID of backend', proname => 'pg_stat_get_backend_userid', provolatile => 's', proparallel => 'r', prorettype => 'oid', proargtypes => 'int4', diff --git a/src/include/storage/sinvaladt.h b/src/include/storage/sinvaladt.h index 91e24189a7..bf739ebdba 100644 --- a/src/include/storage/sinvaladt.h +++ b/src/include/storage/sinvaladt.h @@ -32,7 +32,9 @@ extern Size SInvalShmemSize(void); extern void CreateSharedInvalidationState(void); extern void SharedInvalBackendInit(bool sendOnly); extern PGPROC *BackendIdGetProc(int backendID); -extern void BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmin); +extern void BackendIdGetTransactionIds(int backendID, TransactionId *xid, + TransactionId *xmin, int *nsubxid, + bool *overflowed); extern void SIInsertDataEntries(const SharedInvalidationMessage *data, int n); extern int SIGetDataEntries(SharedInvalidationMessage *data, int datasize); diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h index b582b46e9f..e076adcaa8 100644 --- a/src/include/utils/backend_status.h +++ b/src/include/utils/backend_status.h @@ -266,6 +266,17 @@ typedef struct LocalPgBackendStatus * not. */ TransactionId backend_xmin; + + /* + * Number of cached subtransactions in the current session. + */ + int backend_subxact_count; + + /* + * The number of subtransactions in the current session exceeded the cached + * subtransaction limit. + */ + bool backend_subxact_overflowed; } LocalPgBackendStatus; -- 2.39.5