Allow parallel create index to accumulate buffer usage stats.

Currently, we don't account for buffer usage incurred by parallel workers
for parallel create index.  This commit allows each worker to record the
buffer usage stats and leader backend to accumulate that stats at the
end of the operation.  This will allow pg_stat_statements to display
correct buffer usage stats for (parallel) create index command.

Reported-by: Julien Rouhaud
Author: Sawada Masahiko
Reviewed-by: Dilip Kumar, Julien Rouhaud and Amit Kapila
Backpatch-through: 11, where this was introduced
Discussion: https://postgr.es/m/20200328151721.GB12854@nol

diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index 9d249f7a6b65b903d0f1941dc3fd61161f8d43fd..ba230bbcd2eb5c711c3f387d15297cf64f461235 100644 (file)
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -71,6 +71,7 @@
 #define PARALLEL_KEY_TUPLESORT_SPOOL2  UINT64CONST(0xA000000000000003)
 #define PARALLEL_KEY_QUERY_TEXT            UINT64CONST(0xA000000000000004)
 #define PARALLEL_KEY_WAL_USAGE         UINT64CONST(0xA000000000000005)
+#define PARALLEL_KEY_BUFFER_USAGE      UINT64CONST(0xA000000000000006)
 
 /*
  * DISABLE_LEADER_PARTICIPATION disables the leader's participation in
@@ -194,6 +195,7 @@ typedef struct BTLeader
    Sharedsort *sharedsort2;
    Snapshot    snapshot;
    WalUsage   *walusage;
+   BufferUsage *bufferusage;
 } BTLeader;
 
 /*
@@ -1457,6 +1459,7 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
    BTSpool    *btspool = buildstate->spool;
    BTLeader   *btleader = (BTLeader *) palloc0(sizeof(BTLeader));
    WalUsage   *walusage;
+   BufferUsage *bufferusage;
    bool        leaderparticipates = true;
    char       *sharedquery;
    int         querylen;
@@ -1510,16 +1513,19 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
    }
 
    /*
-    * Estimate space for WalUsage -- PARALLEL_KEY_WAL_USAGE
+    * Estimate space for WalUsage and BufferUsage -- PARALLEL_KEY_WAL_USAGE
+    * and PARALLEL_KEY_BUFFER_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.
+    * If there are no extensions loaded that care, we could skip this.  We
+    * have no way of knowing whether anyone's looking at pgWalUsage or
+    * pgBufferUsage, so do it unconditionally.
     */
    shm_toc_estimate_chunk(&pcxt->estimator,
                           mul_size(sizeof(WalUsage), pcxt->nworkers));
    shm_toc_estimate_keys(&pcxt->estimator, 1);
+   shm_toc_estimate_chunk(&pcxt->estimator,
+                          mul_size(sizeof(BufferUsage), pcxt->nworkers));
+   shm_toc_estimate_keys(&pcxt->estimator, 1);
 
    /* Finally, estimate PARALLEL_KEY_QUERY_TEXT space */
    querylen = strlen(debug_query_string);
@@ -1592,10 +1598,16 @@ _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 */
+   /*
+    * Allocate space for each worker's WalUsage and BufferUsage; 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);
+   bufferusage = shm_toc_allocate(pcxt->toc,
+                                  mul_size(sizeof(BufferUsage), pcxt->nworkers));
+   shm_toc_insert(pcxt->toc, PARALLEL_KEY_BUFFER_USAGE, bufferusage);
 
    /* Launch workers, saving status for leader/caller */
    LaunchParallelWorkers(pcxt);
@@ -1608,6 +1620,7 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
    btleader->sharedsort2 = sharedsort2;
    btleader->snapshot = snapshot;
    btleader->walusage = walusage;
+   btleader->bufferusage = bufferusage;
 
    /* If no workers were successfully launched, back out (do serial build) */
    if (pcxt->nworkers_launched == 0)
@@ -1646,7 +1659,7 @@ _bt_end_parallel(BTLeader *btleader)
     * or we might get incomplete data.)
     */
    for (i = 0; i < btleader->pcxt->nworkers_launched; i++)
-       InstrAccumParallelQuery(NULL, &btleader->walusage[i]);
+       InstrAccumParallelQuery(&btleader->bufferusage[i], &btleader->walusage[i]);
 
    /* Free last reference to MVCC snapshot, if one was used */
    if (IsMVCCSnapshot(btleader->snapshot))
@@ -1779,6 +1792,7 @@ _bt_parallel_build_main(dsm_segment *seg, shm_toc *toc)
    LOCKMODE    heapLockmode;
    LOCKMODE    indexLockmode;
    WalUsage   *walusage;
+   BufferUsage *bufferusage;
    int         sortmem;
 
 #ifdef BTREE_BUILD_STATS
@@ -1848,9 +1862,11 @@ _bt_parallel_build_main(dsm_segment *seg, shm_toc *toc)
    _bt_parallel_scan_and_sort(btspool, btspool2, btshared, sharedsort,
                               sharedsort2, sortmem, false);
 
-   /* Report WAL usage during parallel execution */
+   /* Report WAL/buffer usage during parallel execution */
+   bufferusage = shm_toc_lookup(toc, PARALLEL_KEY_BUFFER_USAGE, false);
    walusage = shm_toc_lookup(toc, PARALLEL_KEY_WAL_USAGE, false);
-   InstrEndParallelQuery(NULL, &walusage[ParallelWorkerNumber]);
+   InstrEndParallelQuery(&bufferusage[ParallelWorkerNumber],
+                         &walusage[ParallelWorkerNumber]);
 
 #ifdef BTREE_BUILD_STATS
    if (log_btree_build_stats)

diff --git a/src/backend/executor/instrument.c b/src/backend/executor/instrument.c
index 74ee4808e364d61f4b6f7d65d283b3ef0c24cb8a..3b9c6aebb929e54b38ff5bdae7f6628fd564c32c 100644 (file)
--- a/src/backend/executor/instrument.c
+++ b/src/backend/executor/instrument.c
@@ -188,11 +188,8 @@ InstrStartParallelQuery(void)
 void
 InstrEndParallelQuery(BufferUsage *bufusage, WalUsage *walusage)
 {
-   if (bufusage)
-   {
-       memset(bufusage, 0, sizeof(BufferUsage));
-       BufferUsageAccumDiff(bufusage, &pgBufferUsage, &save_pgBufferUsage);
-   }
+   memset(bufusage, 0, sizeof(BufferUsage));
+   BufferUsageAccumDiff(bufusage, &pgBufferUsage, &save_pgBufferUsage);
    memset(walusage, 0, sizeof(WalUsage));
    WalUsageAccumDiff(walusage, &pgWalUsage, &save_pgWalUsage);
 }
@@ -201,8 +198,7 @@ InstrEndParallelQuery(BufferUsage *bufusage, WalUsage *walusage)
 void
 InstrAccumParallelQuery(BufferUsage *bufusage, WalUsage *walusage)
 {
-   if (bufusage)
-       BufferUsageAdd(&pgBufferUsage, bufusage);
+   BufferUsageAdd(&pgBufferUsage, bufusage);
    WalUsageAdd(&pgWalUsage, walusage);
 }