Fix VACUUM's reporting of dead-tuple counts to the stats collector.

Historically, VACUUM has just reported its new_rel_tuples estimate
(the same thing it puts into pg_class.reltuples) to the stats collector.
That number counts both live and dead-but-not-yet-reclaimable tuples.
This behavior may once have been right, but modern versions of the
pgstats code track live and dead tuple counts separately, so putting
the total into n_live_tuples and zero into n_dead_tuples is surely
pretty bogus.  Fix it to report live and dead tuple counts separately.

This doesn't really do much for situations where updating transactions
commit concurrently with a VACUUM scan (possibly causing double-counting or
omission of the tuples they add or delete); but it's clearly an improvement
over what we were doing before.

Hari Babu, reviewed by Amit Kapila

diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index e0000e6be32d4afc2fe1f2a2df9fa35b85670b26..75e5f157eaaa1242d8936f2aec98a515cf3d69b3 100644 (file)
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -106,6 +106,7 @@ typedef struct LVRelStats
        double          scanned_tuples; /* counts only tuples on scanned pages */
        double          old_rel_tuples; /* previous value of pg_class.reltuples */
        double          new_rel_tuples; /* new estimated total # of tuples */
+       double          new_dead_tuples;        /* new estimated total # of dead tuples */
        BlockNumber pages_removed;
        double          tuples_deleted;
        BlockNumber nonempty_pages; /* actually, last nonempty page + 1 */
@@ -185,6 +186,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
        BlockNumber new_rel_pages;
        double          new_rel_tuples;
        BlockNumber new_rel_allvisible;
+       double          new_live_tuples;
        TransactionId new_frozen_xid;
        MultiXactId new_min_multi;
 
@@ -307,9 +309,14 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
                                                new_min_multi);
 
        /* report results to the stats collector, too */
+       new_live_tuples = new_rel_tuples - vacrelstats->new_dead_tuples;
+       if (new_live_tuples < 0)
+               new_live_tuples = 0;    /* just in case */
+
        pgstat_report_vacuum(RelationGetRelid(onerel),
                                                 onerel->rd_rel->relisshared,
-                                                new_rel_tuples);
+                                                new_live_tuples,
+                                                vacrelstats->new_dead_tuples);
 
        /* and log the action if appropriate */
        if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0)
@@ -334,7 +341,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
                        ereport(LOG,
                                        (errmsg("automatic vacuum of table \"%s.%s.%s\": index scans: %d\n"
                                                        "pages: %d removed, %d remain\n"
-                                                       "tuples: %.0f removed, %.0f remain\n"
+                                                       "tuples: %.0f removed, %.0f remain, %.0f are dead but not yet removable\n"
                                                        "buffer usage: %d hits, %d misses, %d dirtied\n"
                                          "avg read rate: %.3f MB/s, avg write rate: %.3f MB/s\n"
                                                        "system usage: %s",
@@ -346,6 +353,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
                                                        vacrelstats->rel_pages,
                                                        vacrelstats->tuples_deleted,
                                                        vacrelstats->new_rel_tuples,
+                                                       vacrelstats->new_dead_tuples,
                                                        VacuumPageHit,
                                                        VacuumPageMiss,
                                                        VacuumPageDirty,
@@ -1036,6 +1044,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
        /* save stats for use later */
        vacrelstats->scanned_tuples = num_tuples;
        vacrelstats->tuples_deleted = tups_vacuumed;
+       vacrelstats->new_dead_tuples = nkeep;
 
        /* now we can compute the new value for pg_class.reltuples */
        vacrelstats->new_rel_tuples = vac_estimate_reltuples(onerel, false,

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index ffe43acd6bd5b2f130744202a59819d205c447c5..1c3b481015d14c9ede4b3bd2426e930d021beeb6 100644 (file)
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -1327,7 +1327,8 @@ pgstat_report_autovac(Oid dboid)
  * ---------
  */
 void
-pgstat_report_vacuum(Oid tableoid, bool shared, PgStat_Counter tuples)
+pgstat_report_vacuum(Oid tableoid, bool shared,
+                                        PgStat_Counter livetuples, PgStat_Counter deadtuples)
 {
        PgStat_MsgVacuum msg;
 
@@ -1339,7 +1340,8 @@ pgstat_report_vacuum(Oid tableoid, bool shared, PgStat_Counter tuples)
        msg.m_tableoid = tableoid;
        msg.m_autovacuum = IsAutoVacuumWorkerProcess();
        msg.m_vacuumtime = GetCurrentTimestamp();
-       msg.m_tuples = tuples;
+       msg.m_live_tuples = livetuples;
+       msg.m_dead_tuples = deadtuples;
        pgstat_send(&msg, sizeof(msg));
 }
 
@@ -4809,9 +4811,8 @@ pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len)
 
        tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
 
-       tabentry->n_live_tuples = msg->m_tuples;
-       /* Resetting dead_tuples to 0 is an approximation ... */
-       tabentry->n_dead_tuples = 0;
+       tabentry->n_live_tuples = msg->m_live_tuples;
+       tabentry->n_dead_tuples = msg->m_dead_tuples;
 
        if (msg->m_autovacuum)
        {

diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 96ecc3aff656f898b3f3c43170f4f6a28a11db96..0b458e59bb2a425a94fde5de07356c2cd67b0012 100644 (file)
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -333,7 +333,8 @@ typedef struct PgStat_MsgVacuum
        Oid                     m_tableoid;
        bool            m_autovacuum;
        TimestampTz m_vacuumtime;
-       PgStat_Counter m_tuples;
+       PgStat_Counter m_live_tuples;
+       PgStat_Counter m_dead_tuples;
 } PgStat_MsgVacuum;
 
 
@@ -775,7 +776,7 @@ extern void pgstat_reset_single_counter(Oid objectid, PgStat_Single_Reset_Type t
 
 extern void pgstat_report_autovac(Oid dboid);
 extern void pgstat_report_vacuum(Oid tableoid, bool shared,
-                                        PgStat_Counter tuples);
+                                        PgStat_Counter livetuples, PgStat_Counter deadtuples);
 extern void pgstat_report_analyze(Relation rel,
                                          PgStat_Counter livetuples, PgStat_Counter deadtuples);