pgstat: scaffolding for transactional stats creation / drop.

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 <[email protected]>
Reviewed-By: Thomas Munro <[email protected]>
Reviewed-By: Kyotaro Horiguchi <[email protected]>
Discussion: https://postgr.es/m/[email protected]

1 files changed, 10 insertions, 1 deletions

diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 9235f4dc4ce..7981a816565 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -1049,6 +1049,9 @@ extern void pgstat_report_connect(Oid dboid);
  * Functions in pgstat_function.c
  */
 
+extern void pgstat_create_function(Oid proid);
+extern void pgstat_drop_function(Oid proid);
+
 struct FunctionCallInfoBaseData;
 extern void pgstat_init_function_usage(struct FunctionCallInfoBaseData *fcinfo,
 									   PgStat_FunctionCallUsage *fcu);
@@ -1062,6 +1065,8 @@ extern PgStat_BackendFunctionEntry *find_funcstat_entry(Oid func_id);
  * Functions in pgstat_relation.c
  */
 
+extern void pgstat_create_relation(Relation rel);
+extern void pgstat_drop_relation(Relation rel);
 extern void pgstat_copy_relation_stats(Relation dstrel, Relation srcrel);
 
 extern void pgstat_relation_init(Relation rel);
@@ -1158,7 +1163,8 @@ extern int	pgstat_slru_index(const char *name);
  */
 
 extern void pgstat_report_subscription_error(Oid subid, bool is_apply_error);
-extern void pgstat_report_subscription_drop(Oid subid);
+extern void pgstat_create_subscription(Oid subid);
+extern void pgstat_drop_subscription(Oid subid);
 
 
 /*
@@ -1169,6 +1175,9 @@ extern void AtEOXact_PgStat(bool isCommit, bool parallel);
 extern void AtEOSubXact_PgStat(bool isCommit, int nestDepth);
 extern void AtPrepare_PgStat(void);
 extern void PostPrepare_PgStat(void);
+struct xl_xact_stats_item;
+extern int	pgstat_get_transactional_drops(bool isCommit, struct xl_xact_stats_item **items);
+extern void pgstat_execute_transactional_drops(int ndrops, struct xl_xact_stats_item *items, bool is_redo);
 
 
 /*