Add dead items memory usage to VACUUM (VERBOSE) and autovacuum logs.

This commit adds the total memory allocated during vacuum, the number
of times the dead items storage was reset, and the configured memory
limit. This helps users understand how much memory VACUUM required,
and such information can be used to avoid multiple index scans.

Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CAHza6qcPitBCkyiKJosDTt3bmxMvzZOTONoebwCkBZrr3rk65Q%40mail.gmail.com

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 30778a15639e790fcd99ccfba26b3c46a031b6fd..5fa1151e169cb15e05f819ed6ec7327b33a34ebf 100644 (file)
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -347,6 +347,8 @@ typedef struct LVRelState
 
        /* Instrumentation counters */
        int                     num_index_scans;
+       int                     num_dead_items_resets;
+       Size            total_dead_items_bytes;
        /* Counters that follow are only for scanned_pages */
        int64           tuples_deleted; /* # deleted from table */
        int64           tuples_frozen;  /* # newly frozen */
@@ -645,6 +647,7 @@ heap_vacuum_rel(Relation rel, const VacuumParams params,
        BufferUsage startbufferusage = pgBufferUsage;
        ErrorContextCallback errcallback;
        char      **indnames = NULL;
+       Size            dead_items_max_bytes = 0;
 
        verbose = (params.options & VACOPT_VERBOSE) != 0;
        instrument = (verbose || (AmAutoVacuumWorkerProcess() &&
@@ -767,6 +770,8 @@ heap_vacuum_rel(Relation rel, const VacuumParams params,
 
        /* Initialize remaining counters (be tidy) */
        vacrel->num_index_scans = 0;
+       vacrel->num_dead_items_resets = 0;
+       vacrel->total_dead_items_bytes = 0;
        vacrel->tuples_deleted = 0;
        vacrel->tuples_frozen = 0;
        vacrel->lpdead_items = 0;
@@ -864,6 +869,14 @@ heap_vacuum_rel(Relation rel, const VacuumParams params,
         */
        lazy_scan_heap(vacrel);
 
+       /*
+        * Save dead items max_bytes and update the memory usage statistics before
+        * cleanup, they are freed in parallel vacuum cases during
+        * dead_items_cleanup().
+        */
+       dead_items_max_bytes = vacrel->dead_items_info->max_bytes;
+       vacrel->total_dead_items_bytes += TidStoreMemoryUsage(vacrel->dead_items);
+
        /*
         * Free resources managed by dead_items_alloc.  This ends parallel mode in
         * passing when necessary.
@@ -1167,6 +1180,22 @@ heap_vacuum_rel(Relation rel, const VacuumParams params,
                                                         walusage.wal_bytes,
                                                         walusage.wal_fpi_bytes,
                                                         walusage.wal_buffers_full);
+
+                       /*
+                        * Report the dead items memory usage.
+                        *
+                        * The num_dead_items_resets counter increases when we reset the
+                        * collected dead items, so the counter is non-zero if at least
+                        * one dead items are collected, even if index vacuuming is
+                        * disabled.
+                        */
+                       appendStringInfo(&buf,
+                                                        ngettext("memory usage: dead item storage %.2f MB accumulated across %d reset (limit %.2f MB each)\n",
+                                                                         "memory usage: dead item storage %.2f MB accumulated across %d resets (limit %.2f MB each)\n",
+                                                                         vacrel->num_dead_items_resets),
+                                                        (double) vacrel->total_dead_items_bytes / (1024 * 1024),
+                                                        vacrel->num_dead_items_resets,
+                                                        (double) dead_items_max_bytes / (1024 * 1024));
                        appendStringInfo(&buf, _("system usage: %s"), pg_rusage_show(&ru0));
 
                        ereport(verbose ? INFO : LOG,
@@ -3617,6 +3646,10 @@ dead_items_add(LVRelState *vacrel, BlockNumber blkno, OffsetNumber *offsets,
 static void
 dead_items_reset(LVRelState *vacrel)
 {
+       /* Update statistics for dead items */
+       vacrel->num_dead_items_resets++;
+       vacrel->total_dead_items_bytes += TidStoreMemoryUsage(vacrel->dead_items);
+
        if (ParallelVacuumIsActive(vacrel))
        {
                parallel_vacuum_reset_dead_items(vacrel->pvs);