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pgstat: scaffolding for transactional stats creation / drop.

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One problematic part of the current statistics collector design is that there
is no reliable way of getting rid of statistics entries. Because of that
pgstat_vacuum_stat() (called by [auto-]vacuum) matches all stats for the
current database with the catalog contents and tries to drop now-superfluous
entries. That's quite expensive. What's worse, it doesn't work on physical
replicas, despite physical replicas collection statistics entries.

This commit introduces infrastructure to create / drop statistics entries
transactionally, together with the underlying catalog objects (functions,
relations, subscriptions). pgstat_xact.c maintains a list of stats entries
created / dropped transactionally in the current transaction. To ensure the
removal of statistics entries is durable dropped statistics entries are
included in commit / abort (and prepare) records, which also ensures that
stats entries are dropped on standbys.

Statistics entries created separately from creating the underlying catalog
object (e.g. when stats were previously lost due to an immediate restart)
are *not* WAL logged. However that can only happen outside of the transaction
creating the catalog object, so it does not lead to "leaked" statistics
entries.

For this to work, functions creating / dropping functions / relations /
subscriptions need to call into pgstat. For subscriptions this was already
done when dropping subscriptions, via pgstat_report_subscription_drop() (now
renamed to pgstat_drop_subscription()).

This commit does not actually drop stats yet, it just provides the
infrastructure. It is however a largely independent piece of infrastructure,
so committing it separately makes sense.

Bumps XLOG_PAGE_MAGIC.

Author: Andres Freund <andres@anarazel.de>
Reviewed-By: Thomas Munro <thomas.munro@gmail.com>
Reviewed-By: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20220303021600.hs34ghqcw6zcokdh@alap3.anarazel.de
This commit is contained in:
Andres Freund
2022-04-06 18:22:22 -07:00
parent 8fb580a35c
commit 8b1dccd37c
18 changed files with 526 additions and 38 deletions
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40
src/include/access/xact.h
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@ -180,6 +180,7 @@ typedef struct SavedTransactionCharacteristics
#define XACT_XINFO_HAS_ORIGIN (1U << 5)
#define XACT_XINFO_HAS_AE_LOCKS (1U << 6)
#define XACT_XINFO_HAS_GID (1U << 7)
#define XACT_XINFO_HAS_DROPPED_STATS (1U << 8)
/*
* Also stored in xinfo, these indicating a variety of additional actions that
@ -230,7 +231,7 @@ typedef struct xl_xact_assignment
typedef struct xl_xact_xinfo
{
/*
* Even though we right now only require 1 byte of space in xinfo we use
* Even though we right now only require two bytes of space in xinfo we use
* four so following records don't have to care about alignment. Commit
* records can be large, so copying large portions isn't attractive.
*/
@ -257,6 +258,27 @@ typedef struct xl_xact_relfilenodes
} xl_xact_relfilenodes;
#define MinSizeOfXactRelfilenodes offsetof(xl_xact_relfilenodes, xnodes)
/*
* A transactionally dropped statistics entry.
*
* Declared here rather than pgstat.h because pgstat.h can't be included from
* frontend code, but the WAL format needs to be readable by frontend
* programs.
*/
typedef struct xl_xact_stats_item
{
int kind;
Oid dboid;
Oid objoid;
} xl_xact_stats_item;
typedef struct xl_xact_stats_items
{
int nitems;
xl_xact_stats_item items[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_stats_items;
#define MinSizeOfXactStatsItems offsetof(xl_xact_stats_items, items)
typedef struct xl_xact_invals
{
int nmsgs; /* number of shared inval msgs */
@ -283,6 +305,7 @@ typedef struct xl_xact_commit
/* xl_xact_dbinfo follows if XINFO_HAS_DBINFO */
/* xl_xact_subxacts follows if XINFO_HAS_SUBXACT */
/* xl_xact_relfilenodes follows if XINFO_HAS_RELFILENODES */
/* xl_xact_stats_items follows if XINFO_HAS_DROPPED_STATS */
/* xl_xact_invals follows if XINFO_HAS_INVALS */
/* xl_xact_twophase follows if XINFO_HAS_TWOPHASE */
/* twophase_gid follows if XINFO_HAS_GID. As a null-terminated string. */
@ -298,6 +321,7 @@ typedef struct xl_xact_abort
/* xl_xact_dbinfo follows if XINFO_HAS_DBINFO */
/* xl_xact_subxacts follows if XINFO_HAS_SUBXACT */
/* xl_xact_relfilenodes follows if XINFO_HAS_RELFILENODES */
/* xl_xact_stats_items follows if XINFO_HAS_DROPPED_STATS */
/* No invalidation messages needed. */
/* xl_xact_twophase follows if XINFO_HAS_TWOPHASE */
/* twophase_gid follows if XINFO_HAS_GID. As a null-terminated string. */
@ -316,6 +340,8 @@ typedef struct xl_xact_prepare
int32 nsubxacts; /* number of following subxact XIDs */
int32 ncommitrels; /* number of delete-on-commit rels */
int32 nabortrels; /* number of delete-on-abort rels */
int32 ncommitstats; /* number of stats to drop on commit */
int32 nabortstats; /* number of stats to drop on abort */
int32 ninvalmsgs; /* number of cache invalidation messages */
bool initfileinval; /* does relcache init file need invalidation? */
uint16 gidlen; /* length of the GID - GID follows the header */
@ -342,6 +368,9 @@ typedef struct xl_xact_parsed_commit
int nrels;
RelFileNode *xnodes;
int nstats;
xl_xact_stats_item *stats;
int nmsgs;
SharedInvalidationMessage *msgs;
@ -349,6 +378,8 @@ typedef struct xl_xact_parsed_commit
char twophase_gid[GIDSIZE]; /* only for 2PC */
int nabortrels; /* only for 2PC */
RelFileNode *abortnodes; /* only for 2PC */
int nabortstats; /* only for 2PC */
xl_xact_stats_item *abortstats; /* only for 2PC */
XLogRecPtr origin_lsn;
TimestampTz origin_timestamp;
@ -370,6 +401,9 @@ typedef struct xl_xact_parsed_abort
int nrels;
RelFileNode *xnodes;
int nstats;
xl_xact_stats_item *stats;
TransactionId twophase_xid; /* only for 2PC */
char twophase_gid[GIDSIZE]; /* only for 2PC */
@ -449,6 +483,8 @@ extern int xactGetCommittedChildren(TransactionId **ptr);
extern XLogRecPtr XactLogCommitRecord(TimestampTz commit_time,
int nsubxacts, TransactionId *subxacts,
int nrels, RelFileNode *rels,
int nstats,
xl_xact_stats_item *stats,
int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInval,
int xactflags,
@ -458,6 +494,8 @@ extern XLogRecPtr XactLogCommitRecord(TimestampTz commit_time,
extern XLogRecPtr XactLogAbortRecord(TimestampTz abort_time,
int nsubxacts, TransactionId *subxacts,
int nrels, RelFileNode *rels,
int nstats,
xl_xact_stats_item *stats,
int xactflags, TransactionId twophase_xid,
const char *twophase_gid);
extern void xact_redo(XLogReaderState *record);