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

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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
This commit is contained in:
Tom Lane 2014-01-18 19:24:20 -05:00
parent 76e91b38ba
commit 115f414124
3 changed files with 20 additions and 9 deletions
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13
src/backend/commands/vacuumlazy.c
View File

@ -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,

11
src/backend/postmaster/pgstat.c
View File

@ -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)
{

5
src/include/pgstat.h
View File

@ -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);