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Add infrastructure to track WAL usage.

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

View File

@@ -139,6 +139,7 @@
#define PARALLEL_VACUUM_KEY_DEAD_TUPLES 2
#define PARALLEL_VACUUM_KEY_QUERY_TEXT 3
#define PARALLEL_VACUUM_KEY_BUFFER_USAGE 4
#define PARALLEL_VACUUM_KEY_WAL_USAGE 5
/*
* Macro to check if we are in a parallel vacuum. If true, we are in the
@@ -275,6 +276,9 @@ typedef struct LVParallelState
/* Points to buffer usage area in DSM */
BufferUsage *buffer_usage;
/* Points to WAL usage area in DSM */
WalUsage *wal_usage;
/*
* The number of indexes that support parallel index bulk-deletion and
* parallel index cleanup respectively.
@@ -2143,8 +2147,8 @@ lazy_parallel_vacuum_indexes(Relation *Irel, IndexBulkDeleteResult **stats,
vacrelstats->dead_tuples, nindexes, vacrelstats);
/*
* Next, accumulate buffer usage. (This must wait for the workers to
* finish, or we might get incomplete data.)
* Next, accumulate buffer and WAL usage. (This must wait for the workers
* to finish, or we might get incomplete data.)
*/
if (nworkers > 0)
{
@@ -2154,7 +2158,7 @@ lazy_parallel_vacuum_indexes(Relation *Irel, IndexBulkDeleteResult **stats,
WaitForParallelWorkersToFinish(lps->pcxt);
for (i = 0; i < lps->pcxt->nworkers_launched; i++)
InstrAccumParallelQuery(&lps->buffer_usage[i]);
InstrAccumParallelQuery(&lps->buffer_usage[i], &lps->wal_usage[i]);
}
/*
@@ -3171,6 +3175,7 @@ begin_parallel_vacuum(Oid relid, Relation *Irel, LVRelStats *vacrelstats,
LVShared *shared;
LVDeadTuples *dead_tuples;
BufferUsage *buffer_usage;
WalUsage *wal_usage;
bool *can_parallel_vacuum;
long maxtuples;
char *sharedquery;
@@ -3255,15 +3260,19 @@ begin_parallel_vacuum(Oid relid, Relation *Irel, LVRelStats *vacrelstats,
shm_toc_estimate_keys(&pcxt->estimator, 1);
/*
* Estimate space for BufferUsage -- PARALLEL_VACUUM_KEY_BUFFER_USAGE.
* Estimate space for BufferUsage and WalUsage --
* PARALLEL_VACUUM_KEY_BUFFER_USAGE and PARALLEL_VACUUM_KEY_WAL_USAGE.
*
* If there are no extensions loaded that care, we could skip this. We
* have no way of knowing whether anyone's looking at pgBufferUsage, so do
* it unconditionally.
* have no way of knowing whether anyone's looking at pgBufferUsage or
* pgWalUsage, so do it unconditionally.
*/
shm_toc_estimate_chunk(&pcxt->estimator,
mul_size(sizeof(BufferUsage), pcxt->nworkers));
shm_toc_estimate_keys(&pcxt->estimator, 1);
shm_toc_estimate_chunk(&pcxt->estimator,
mul_size(sizeof(WalUsage), pcxt->nworkers));
shm_toc_estimate_keys(&pcxt->estimator, 1);
/* Finally, estimate PARALLEL_VACUUM_KEY_QUERY_TEXT space */
querylen = strlen(debug_query_string);
@@ -3299,11 +3308,18 @@ begin_parallel_vacuum(Oid relid, Relation *Irel, LVRelStats *vacrelstats,
shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_DEAD_TUPLES, dead_tuples);
vacrelstats->dead_tuples = dead_tuples;
/* Allocate space for each worker's BufferUsage; no need to initialize */
/*
* Allocate space for each worker's BufferUsage and WalUsage; no need to
* initialize
*/
buffer_usage = shm_toc_allocate(pcxt->toc,
mul_size(sizeof(BufferUsage), pcxt->nworkers));
shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_BUFFER_USAGE, buffer_usage);
lps->buffer_usage = buffer_usage;
wal_usage = shm_toc_allocate(pcxt->toc,
mul_size(sizeof(WalUsage), pcxt->nworkers));
shm_toc_insert(pcxt->toc, PARALLEL_VACUUM_KEY_WAL_USAGE, wal_usage);
lps->wal_usage = wal_usage;
/* Store query string for workers */
sharedquery = (char *) shm_toc_allocate(pcxt->toc, querylen + 1);
@@ -3435,6 +3451,7 @@ parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
LVShared *lvshared;
LVDeadTuples *dead_tuples;
BufferUsage *buffer_usage;
WalUsage *wal_usage;
int nindexes;
char *sharedquery;
IndexBulkDeleteResult **stats;
@@ -3511,9 +3528,11 @@ parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
parallel_vacuum_index(indrels, stats, lvshared, dead_tuples, nindexes,
&vacrelstats);
/* Report buffer usage during parallel execution */
/* Report buffer/WAL usage during parallel execution */
buffer_usage = shm_toc_lookup(toc, PARALLEL_VACUUM_KEY_BUFFER_USAGE, false);
InstrEndParallelQuery(&buffer_usage[ParallelWorkerNumber]);
wal_usage = shm_toc_lookup(toc, PARALLEL_VACUUM_KEY_WAL_USAGE, false);
InstrEndParallelQuery(&buffer_usage[ParallelWorkerNumber],
&wal_usage[ParallelWorkerNumber]);
/* Pop the error context stack */
error_context_stack = errcallback.previous;