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Add infrastructure to track WAL usage.

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This allows gathering the WAL generation statistics for each statement
execution.  The three statistics that we collect are the number of WAL
records, the number of full page writes and the amount of WAL bytes
generated.

This helps the users who have write-intensive workload to see the impact
of I/O due to WAL.  This further enables us to see approximately what
percentage of overall WAL is due to full page writes.

In the future, we can extend this functionality to allow us to compute the
the exact amount of WAL data due to full page writes.

This patch in itself is just an infrastructure to compute WAL usage data.
The upcoming patches will expose this data via explain, auto_explain,
pg_stat_statements and verbose (auto)vacuum output.

Author: Kirill Bychik, Julien Rouhaud
Reviewed-by: Dilip Kumar, Fujii Masao and Amit Kapila
Discussion: https://postgr.es/m/CAB-hujrP8ZfUkvL5OYETipQwA=e3n7oqHFU=4ZLxWS_Cza3kQQ@mail.gmail.com
This commit is contained in:
Amit Kapila
2020-04-04 10:02:08 +05:30
parent 0588ee63aa
commit df3b181499
10 changed files with 182 additions and 32 deletions
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40
src/backend/access/nbtree/nbtsort.c
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@@ -67,6 +67,7 @@
#include "access/xloginsert.h"
#include "catalog/index.h"
#include "commands/progress.h"
#include "executor/instrument.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/smgr.h"
@@ -81,6 +82,7 @@
#define PARALLEL_KEY_TUPLESORT UINT64CONST(0xA000000000000002)
#define PARALLEL_KEY_TUPLESORT_SPOOL2 UINT64CONST(0xA000000000000003)
#define PARALLEL_KEY_QUERY_TEXT UINT64CONST(0xA000000000000004)
#define PARALLEL_KEY_WAL_USAGE UINT64CONST(0xA000000000000005)
/*
* DISABLE_LEADER_PARTICIPATION disables the leader's participation in
@@ -203,6 +205,7 @@ typedef struct BTLeader
Sharedsort *sharedsort;
Sharedsort *sharedsort2;
Snapshot snapshot;
WalUsage *walusage;
} BTLeader;
/*
@@ -1476,6 +1479,7 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
Sharedsort *sharedsort2;
BTSpool *btspool = buildstate->spool;
BTLeader *btleader = (BTLeader *) palloc0(sizeof(BTLeader));
WalUsage *walusage;
bool leaderparticipates = true;
char *sharedquery;
int querylen;
@@ -1528,6 +1532,18 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
shm_toc_estimate_keys(&pcxt->estimator, 3);
}
/*
* Estimate space for WalUsage -- PARALLEL_KEY_WAL_USAGE
*
* WalUsage during execution of maintenance command can be used by an
* extension that reports the WAL usage, such as pg_stat_statements. We
* have no way of knowing whether anyone's looking at pgWalUsage, so do it
* unconditionally.
*/
shm_toc_estimate_chunk(&pcxt->estimator,
mul_size(sizeof(WalUsage), pcxt->nworkers));
shm_toc_estimate_keys(&pcxt->estimator, 1);
/* Finally, estimate PARALLEL_KEY_QUERY_TEXT space */
querylen = strlen(debug_query_string);
shm_toc_estimate_chunk(&pcxt->estimator, querylen + 1);
@@ -1599,6 +1615,11 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
memcpy(sharedquery, debug_query_string, querylen + 1);
shm_toc_insert(pcxt->toc, PARALLEL_KEY_QUERY_TEXT, sharedquery);
/* Allocate space for each worker's WalUsage; no need to initialize */
walusage = shm_toc_allocate(pcxt->toc,
mul_size(sizeof(WalUsage), pcxt->nworkers));
shm_toc_insert(pcxt->toc, PARALLEL_KEY_WAL_USAGE, walusage);
/* Launch workers, saving status for leader/caller */
LaunchParallelWorkers(pcxt);
btleader->pcxt = pcxt;
@@ -1609,6 +1630,7 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
btleader->sharedsort = sharedsort;
btleader->sharedsort2 = sharedsort2;
btleader->snapshot = snapshot;
btleader->walusage = walusage;
/* If no workers were successfully launched, back out (do serial build) */
if (pcxt->nworkers_launched == 0)
@@ -1637,8 +1659,18 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
static void
_bt_end_parallel(BTLeader *btleader)
{
int i;
/* Shutdown worker processes */
WaitForParallelWorkersToFinish(btleader->pcxt);
/*
* Next, accumulate WAL usage. (This must wait for the workers to finish,
* or we might get incomplete data.)
*/
for (i = 0; i < btleader->pcxt->nworkers_launched; i++)
InstrAccumParallelQuery(NULL, &btleader->walusage[i]);
/* Free last reference to MVCC snapshot, if one was used */
if (IsMVCCSnapshot(btleader->snapshot))
UnregisterSnapshot(btleader->snapshot);
@@ -1769,6 +1801,7 @@ _bt_parallel_build_main(dsm_segment *seg, shm_toc *toc)
Relation indexRel;
LOCKMODE heapLockmode;
LOCKMODE indexLockmode;
WalUsage *walusage;
int sortmem;
#ifdef BTREE_BUILD_STATS
@@ -1830,11 +1863,18 @@ _bt_parallel_build_main(dsm_segment *seg, shm_toc *toc)
tuplesort_attach_shared(sharedsort2, seg);
}
/* Prepare to track buffer usage during parallel execution */
InstrStartParallelQuery();
/* Perform sorting of spool, and possibly a spool2 */
sortmem = maintenance_work_mem / btshared->scantuplesortstates;
_bt_parallel_scan_and_sort(btspool, btspool2, btshared, sharedsort,
sharedsort2, sortmem, false);
/* Report WAL usage during parallel execution */
walusage = shm_toc_lookup(toc, PARALLEL_KEY_WAL_USAGE, false);
InstrEndParallelQuery(NULL, &walusage[ParallelWorkerNumber]);
#ifdef BTREE_BUILD_STATS
if (log_btree_build_stats)
{