From 6d84255845e9f945f96a30e787befe93fb162695 Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Wed, 24 Nov 2021 12:07:37 -0500 Subject: [PATCH v17 5/7] Add system view tracking IO ops per backend type Add pg_stat_buffers, a system view which tracks the number of IO operations (allocs, writes, fsyncs, and extends) done through each IO path (e.g. shared buffers, local buffers, unbuffered IO) by each type of backend. Some of these should always be zero. For example, checkpointer does not use a BufferAccessStrategy (currently), so the "strategy" IO path for checkpointer will be 0 for all IO operations (alloc, write, fsync, and extend). All possible combinations of IO Path and IO Op are enumerated in the view but not all are populated or even possible at this point. All backends increment a counter in their PgBackendStatus when performing an IO operation. On exit, backends send these stats to the stats collector to be persisted. When the pg_stat_buffers view is queried, one backend will sum live backends' stats with saved stats from exited backends and subtract saved reset stats, returning the total. Each row of the view is stats for a particular backend type for a particular IO path (e.g. shared buffer accesses by checkpointer) and each column in the view is the total number of IO operations done (e.g. writes). So a cell in the view would be, for example, the number of shared buffers written by checkpointer since the last stats reset. Discussion: https://www.postgresql.org/message-id/flat/20210415235954.qcypb4urtovzkat5%40alap3.anarazel.de#724d5cce4bcb587f9167b80a5824bc5c --- doc/src/sgml/monitoring.sgml | 110 +++++++++++++- src/backend/catalog/system_views.sql | 11 ++ src/backend/postmaster/pgstat.c | 13 ++ src/backend/utils/activity/backend_status.c | 19 ++- src/backend/utils/adt/pgstatfuncs.c | 154 ++++++++++++++++++++ src/include/catalog/pg_proc.dat | 9 ++ src/include/pgstat.h | 1 + src/include/utils/backend_status.h | 5 + src/test/regress/expected/rules.out | 8 + 9 files changed, 327 insertions(+), 3 deletions(-) diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index bda3eef309..b16952d439 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -435,6 +435,15 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser + + pg_stat_bufferspg_stat_buffers + A row for each IO path for each backend type showing + statistics about backend IO operations. See + + pg_stat_buffers for details. + + + pg_stat_walpg_stat_wal One row only, showing statistics about WAL activity. See @@ -3613,6 +3622,101 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i + + <structname>pg_stat_buffers</structname> + + + pg_stat_buffers + + + + The pg_stat_buffers view has a row for each backend + type for each possible IO path, containing global data for the cluster for + that backend and IO path. + + + + <structname>pg_stat_buffers</structname> View + + + + + Column Type + + + Description + + + + + + + backend_type text + + + Type of backend (e.g. background worker, autovacuum worker). + + + + + + io_path text + + + IO path taken (e.g. shared buffers, direct). + + + + + + alloc bigint + + + Number of buffers allocated. + + + + + + extend bigint + + + Number of buffers extended. + + + + + + fsync bigint + + + Number of buffers fsynced. + + + + + + write bigint + + + Number of buffers written. + + + + + + stats_reset timestamp with time zone + + + Time at which these statistics were last reset. + + + + +
+ + + <structname>pg_stat_wal</structname> @@ -5213,8 +5317,10 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i all the counters shown in the pg_stat_bgwriter view, archiver to reset all the counters shown in - the pg_stat_archiver view or wal - to reset all the counters shown in the pg_stat_wal view. + the pg_stat_archiver view, wal + to reset all the counters shown in the pg_stat_wal view, + or buffers to reset all the counters shown in the + pg_stat_buffers view. This function is restricted to superusers by default, but other users diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql index 61b515cdb8..e214d23056 100644 --- a/src/backend/catalog/system_views.sql +++ b/src/backend/catalog/system_views.sql @@ -1076,6 +1076,17 @@ CREATE VIEW pg_stat_bgwriter AS pg_stat_get_buf_alloc() AS buffers_alloc, pg_stat_get_bgwriter_stat_reset_time() AS stats_reset; +CREATE VIEW pg_stat_buffers AS +SELECT + b.backend_type, + b.io_path, + b.alloc, + b.extend, + b.fsync, + b.write, + b.stats_reset +FROM pg_stat_get_buffers() b; + CREATE VIEW pg_stat_wal AS SELECT w.wal_records, diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c index c40b375b9a..9b041cb1b9 100644 --- a/src/backend/postmaster/pgstat.c +++ b/src/backend/postmaster/pgstat.c @@ -2925,6 +2925,19 @@ pgstat_twophase_postabort(TransactionId xid, uint16 info, rec->tuples_inserted + rec->tuples_updated; } +/* + * Support function for SQL-callable pgstat* functions. Returns a pointer to + * the PgStat_BackendIOPathOps structure tracking IO op statistics for both + * exited backends and reset arithmetic. + */ +PgStat_BackendIOPathOps * +pgstat_fetch_exited_backend_buffers(void) +{ + backend_read_statsfile(); + + return &globalStats.buffers; +} + /* ---------- * pgstat_fetch_stat_dbentry() - diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c index 9e9ca3e5a6..f1997441bc 100644 --- a/src/backend/utils/activity/backend_status.c +++ b/src/backend/utils/activity/backend_status.c @@ -50,7 +50,7 @@ int pgstat_track_activity_query_size = 1024; PgBackendStatus *MyBEEntry = NULL; -static PgBackendStatus *BackendStatusArray = NULL; +PgBackendStatus *BackendStatusArray = NULL; static char *BackendAppnameBuffer = NULL; static char *BackendClientHostnameBuffer = NULL; static char *BackendActivityBuffer = NULL; @@ -236,6 +236,23 @@ CreateSharedBackendStatus(void) #endif } +const char * +GetIOPathDesc(IOPath io_path) +{ + switch (io_path) + { + case IOPATH_DIRECT: + return "direct"; + case IOPATH_LOCAL: + return "local"; + case IOPATH_SHARED: + return "shared"; + case IOPATH_STRATEGY: + return "strategy"; + } + return "unknown IO path"; +} + /* * Initialize pgstats backend activity state, and set up our on-proc-exit * hook. Called from InitPostgres and AuxiliaryProcessMain. For auxiliary diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c index f529c1561a..9fd7a8cdb9 100644 --- a/src/backend/utils/adt/pgstatfuncs.c +++ b/src/backend/utils/adt/pgstatfuncs.c @@ -1796,6 +1796,160 @@ pg_stat_get_buf_alloc(PG_FUNCTION_ARGS) PG_RETURN_INT64(pgstat_fetch_stat_bgwriter()->buf_alloc); } +/* +* When adding a new column to the pg_stat_buffers view, add a new enum +* value here above COLUMN_LENGTH. +*/ +enum +{ + COLUMN_BACKEND_TYPE, + COLUMN_IO_PATH, + COLUMN_ALLOCS, + COLUMN_EXTENDS, + COLUMN_FSYNCS, + COLUMN_WRITES, + COLUMN_RESET_TIME, + COLUMN_LENGTH, +}; + +/* + * Helper function to get the correct row in the pg_stat_buffers view. + */ +static inline Datum * +get_pg_stat_buffers_row(Datum all_values[BACKEND_NUM_TYPES][IOPATH_NUM_TYPES][COLUMN_LENGTH], + BackendType backend_type, IOPath io_path) +{ + /* + * Caller must pass in a valid BackendType, as there are no rows for + * B_INVALID. Subtract 1 to arrive at the correct row. + */ + Assert(backend_type > B_INVALID); + return all_values[backend_type - 1][io_path]; +} + +Datum +pg_stat_get_buffers(PG_FUNCTION_ARGS) +{ + PgStat_BackendIOPathOps *backend_io_path_ops; + PgBackendStatus *beentry; + Datum reset_time; + + ReturnSetInfo *rsinfo; + TupleDesc tupdesc; + Tuplestorestate *tupstore; + MemoryContext per_query_ctx; + MemoryContext oldcontext; + + Datum all_values[BACKEND_NUM_TYPES][IOPATH_NUM_TYPES][COLUMN_LENGTH]; + bool all_nulls[BACKEND_NUM_TYPES][IOPATH_NUM_TYPES][COLUMN_LENGTH]; + + rsinfo = (ReturnSetInfo *) fcinfo->resultinfo; + + /* check to see if caller supports us returning a tuplestore */ + if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo)) + ereport(ERROR, + (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), + errmsg("set-valued function called in context that cannot accept a set"))); + if (!(rsinfo->allowedModes & SFRM_Materialize)) + ereport(ERROR, + (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), + errmsg("materialize mode required, but it is not allowed in this context"))); + + /* Build a tuple descriptor for our result type */ + if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE) + elog(ERROR, "return type must be a row type"); + + per_query_ctx = rsinfo->econtext->ecxt_per_query_memory; + oldcontext = MemoryContextSwitchTo(per_query_ctx); + tupstore = tuplestore_begin_heap((bool) (rsinfo->allowedModes & SFRM_Materialize_Random), + false, work_mem); + rsinfo->returnMode = SFRM_Materialize; + rsinfo->setResult = tupstore; + rsinfo->setDesc = tupdesc; + MemoryContextSwitchTo(oldcontext); + + memset(all_values, 0, sizeof(all_values)); + memset(all_nulls, 0, sizeof(all_nulls)); + + /* Loop through all live backends and count their IO Ops for each IO Path */ + beentry = BackendStatusArray; + + for (int i = 0; i < MaxBackends + NUM_AUXPROCTYPES; i++, beentry++) + { + IOOps *io_ops; + + /* Don't count dead backends. They will be added below */ + Assert(beentry->st_backendType >= B_INVALID); + if (beentry->st_procpid == 0 || beentry->st_backendType == B_INVALID) + continue; + + io_ops = beentry->io_path_stats; + + for (int io_path = 0; io_path < IOPATH_NUM_TYPES; io_path++) + { + Datum *row = get_pg_stat_buffers_row(all_values, beentry->st_backendType, io_path); + + /* + * COLUMN_RESET_TIME, COLUMN_BACKEND_TYPE, and COLUMN_IO_PATH will + * all be set when looping through exited backends array + */ + row[COLUMN_ALLOCS] += pg_atomic_read_u64(&io_ops->allocs); + row[COLUMN_EXTENDS] += pg_atomic_read_u64(&io_ops->extends); + row[COLUMN_FSYNCS] += pg_atomic_read_u64(&io_ops->fsyncs); + row[COLUMN_WRITES] += pg_atomic_read_u64(&io_ops->writes); + io_ops++; + } + } + + /* Add stats from all exited backends */ + backend_io_path_ops = pgstat_fetch_exited_backend_buffers(); + + reset_time = TimestampTzGetDatum(backend_io_path_ops->stat_reset_timestamp); + + for (int backend_type_idx = 0; backend_type_idx < BACKEND_NUM_TYPES; backend_type_idx++) + { + PgStatIOOps *io_ops = backend_io_path_ops->ops[backend_type_idx].io_path_ops; + PgStatIOOps *resets = backend_io_path_ops->resets[backend_type_idx].io_path_ops; + + Datum backend_type_desc = + CStringGetTextDatum(GetBackendTypeDesc(backend_type_idx + 1)); + + for (int io_path = 0; io_path < IOPATH_NUM_TYPES; io_path++) + { + /* + * all_values does not include rows for the B_INVALID BackendType + * and get_pg_stat_buffers_row() expects a valid BackendType, so + * add 1 to the backend_type_idx to ensure the correct rows are + * returned for the desired BackendType. + */ + Datum *row = get_pg_stat_buffers_row(all_values, backend_type_idx + 1, io_path); + + row[COLUMN_BACKEND_TYPE] = backend_type_desc; + row[COLUMN_IO_PATH] = CStringGetTextDatum(GetIOPathDesc(io_path)); + row[COLUMN_RESET_TIME] = reset_time; + row[COLUMN_ALLOCS] += io_ops->allocs - resets->allocs; + row[COLUMN_EXTENDS] += io_ops->extends - resets->extends; + row[COLUMN_FSYNCS] += io_ops->fsyncs - resets->fsyncs; + row[COLUMN_WRITES] += io_ops->writes - resets->writes; + io_ops++; + resets++; + } + } + + for (int backend_type_idx = 0; backend_type_idx < BACKEND_NUM_TYPES; backend_type_idx++) + { + for (int io_path = 0; io_path < IOPATH_NUM_TYPES; io_path++) + { + Datum *values = all_values[backend_type_idx][io_path]; + bool *nulls = all_nulls[backend_type_idx][io_path]; + + tuplestore_putvalues(tupstore, tupdesc, values, nulls); + } + } + + return (Datum) 0; +} + /* * Returns statistics of WAL activity */ diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat index 79d787cd26..32253383ba 100644 --- a/src/include/catalog/pg_proc.dat +++ b/src/include/catalog/pg_proc.dat @@ -5654,6 +5654,15 @@ proname => 'pg_stat_get_buf_alloc', provolatile => 's', proparallel => 'r', prorettype => 'int8', proargtypes => '', prosrc => 'pg_stat_get_buf_alloc' }, +{ oid => '8459', descr => 'statistics: counts of all IO operations done to all IO paths by each type of backend.', + proname => 'pg_stat_get_buffers', provolatile => 's', proisstrict => 'f', + prorows => '52', proretset => 't', + proparallel => 'r', prorettype => 'record', proargtypes => '', + proallargtypes => '{text,text,int8,int8,int8,int8,timestamptz}', + proargmodes => '{o,o,o,o,o,o,o}', + proargnames => '{backend_type,io_path,alloc,extend,fsync,write,stats_reset}', + prosrc => 'pg_stat_get_buffers' }, + { oid => '1136', descr => 'statistics: information about WAL activity', proname => 'pg_stat_get_wal', proisstrict => 'f', provolatile => 's', proparallel => 'r', prorettype => 'record', proargtypes => '', diff --git a/src/include/pgstat.h b/src/include/pgstat.h index 2496d7e071..9e1c635108 100644 --- a/src/include/pgstat.h +++ b/src/include/pgstat.h @@ -1278,6 +1278,7 @@ extern void pgstat_sum_io_path_ops(PgStatIOOps *dest, IOOps *src); * generate the pgstat* views. * ---------- */ +extern PgStat_BackendIOPathOps *pgstat_fetch_exited_backend_buffers(void); extern PgStat_StatDBEntry *pgstat_fetch_stat_dbentry(Oid dbid); extern PgStat_StatTabEntry *pgstat_fetch_stat_tabentry(Oid relid); extern PgStat_StatFuncEntry *pgstat_fetch_stat_funcentry(Oid funcid); diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h index acb4a85eef..4dbf32d48e 100644 --- a/src/include/utils/backend_status.h +++ b/src/include/utils/backend_status.h @@ -317,6 +317,7 @@ extern PGDLLIMPORT int pgstat_track_activity_query_size; * ---------- */ extern PGDLLIMPORT PgBackendStatus *MyBEEntry; +extern PGDLLIMPORT PgBackendStatus *BackendStatusArray; /* ---------- @@ -332,6 +333,10 @@ extern void CreateSharedBackendStatus(void); * ---------- */ +/* Utility functions */ +extern const char *GetIOPathDesc(IOPath io_path); + + /* Initialization functions */ extern void pgstat_beinit(void); extern void pgstat_bestart(void); diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out index b58b062b10..5869ce442f 100644 --- a/src/test/regress/expected/rules.out +++ b/src/test/regress/expected/rules.out @@ -1828,6 +1828,14 @@ pg_stat_bgwriter| SELECT pg_stat_get_bgwriter_timed_checkpoints() AS checkpoints pg_stat_get_buf_fsync_backend() AS buffers_backend_fsync, pg_stat_get_buf_alloc() AS buffers_alloc, pg_stat_get_bgwriter_stat_reset_time() AS stats_reset; +pg_stat_buffers| SELECT b.backend_type, + b.io_path, + b.alloc, + b.extend, + b.fsync, + b.write, + b.stats_reset + FROM pg_stat_get_buffers() b(backend_type, io_path, alloc, extend, fsync, write, stats_reset); pg_stat_database| SELECT d.oid AS datid, d.datname, CASE -- 2.32.0