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Use HTAB for replication slot statistics.

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Previously, we used to use the array of size max_replication_slots to
store stats for replication slots. But that had two problems in the cases
where a message for dropping a slot gets lost: 1) the stats for the new
slot are not recorded if the array is full and 2) writing beyond the end
of the array if the user reduces the max_replication_slots.

This commit uses HTAB for replication slot statistics, resolving both
problems. Now, pgstat_vacuum_stat() search for all the dead replication
slots in stats hashtable and tell the collector to remove them. To avoid
showing the stats for the already-dropped slots, pg_stat_replication_slots
view searches slot stats by the slot name taken from pg_replication_slots.

Also, we send a message for creating a slot at slot creation, initializing
the stats. This reduces the possibility that the stats are accumulated
into the old slot stats when a message for dropping a slot gets lost.

Reported-by: Andres Freund
Author: Sawada Masahiko, test case by Vignesh C
Reviewed-by: Amit Kapila, Vignesh C, Dilip Kumar
Discussion: https://postgr.es/m/20210319185247.ldebgpdaxsowiflw@alap3.anarazel.de
This commit is contained in:
Amit Kapila
2021-04-27 09:09:11 +05:30
parent e7eea52b2d
commit 3fa17d3771
12 changed files with 389 additions and 260 deletions
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10
src/include/pgstat.h
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@ -541,6 +541,7 @@ typedef struct PgStat_MsgReplSlot
{
PgStat_MsgHdr m_hdr;
NameData m_slotname;
bool m_create;
bool m_drop;
PgStat_Counter m_spill_txns;
PgStat_Counter m_spill_count;
@ -917,7 +918,7 @@ typedef struct PgStat_SLRUStats
/*
* Replication slot statistics kept in the stats collector
*/
typedef struct PgStat_ReplSlotStats
typedef struct PgStat_StatReplSlotEntry
{
NameData slotname;
PgStat_Counter spill_txns;
@ -929,7 +930,7 @@ typedef struct PgStat_ReplSlotStats
PgStat_Counter total_txns;
PgStat_Counter total_bytes;
TimestampTz stat_reset_timestamp;
} PgStat_ReplSlotStats;
} PgStat_StatReplSlotEntry;
/*
@ -1031,7 +1032,8 @@ extern void pgstat_report_recovery_conflict(int reason);
extern void pgstat_report_deadlock(void);
extern void pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount);
extern void pgstat_report_checksum_failure(void);
extern void pgstat_report_replslot(const PgStat_ReplSlotStats *repSlotStat);
extern void pgstat_report_replslot(const PgStat_StatReplSlotEntry *repSlotStat);
extern void pgstat_report_replslot_create(const char *slotname);
extern void pgstat_report_replslot_drop(const char *slotname);
extern void pgstat_initialize(void);
@ -1129,7 +1131,7 @@ extern PgStat_ArchiverStats *pgstat_fetch_stat_archiver(void);
extern PgStat_GlobalStats *pgstat_fetch_global(void);
extern PgStat_WalStats *pgstat_fetch_stat_wal(void);
extern PgStat_SLRUStats *pgstat_fetch_slru(void);
extern PgStat_ReplSlotStats *pgstat_fetch_replslot(int *nslots_p);
extern PgStat_StatReplSlotEntry *pgstat_fetch_replslot(NameData slotname);
extern PgStat_RecoveryPrefetchStats *pgstat_fetch_recoveryprefetch(void);
extern void pgstat_count_slru_page_zeroed(int slru_idx);