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Improve memory handling across SQL-callable backup functions

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Since pg_backup_start() and pg_backup_stop() exist, the tablespace map
data and the backup state data (backup_label string until 7d70809) have
been allocated in the TopMemoryContext.  This approach would cause
memory leaks in the session calling these functions if failures happen
before pg_backup_stop() ends, leaking more memory on repeated failures.
Both things need little memory so that would not be really noticeable
for most users, except perhaps connection poolers with long-lived
connections able to trigger backup failures with these functions.

This commit improves the logic in this area by not allocating anymore
the backup-related data that needs to travel across the SQL-callable
backup functions in TopMemoryContext, by using instead a dedicated
memory context child of TopMemoryContext.  The memory context is created
in pg_backup_start() and deleted when finishing pg_backup_stop().  In
the event of an in-flight failure, this memory context gets reset in the
follow-up pg_backup_start() call, so as we are sure that only one run
worth of data is leaked at any time.  Some cleanup was already done for
the backup data on a follow-up call of pg_backup_start(), but using a
memory context makes the whole simpler.

BASE_BACKUP commands are executed in isolation, relying on the memory
context created for replication commands, hence these do not need such
an extra logic.

Author: Bharath Rupireddy
Reviewed-by: Robert Haas, Alvaro Herrera, Cary Huang, Michael Paquier
Discussion: https://postgr.es/m/CALj2ACXqvfKF2B0beQ=aJMdWnpNohmBPsRg=EDQj_6y1t2O8mQ@mail.gmail.com
This commit is contained in:
Michael Paquier 2022-10-22 11:54:02 +09:00
parent 1f0c4fa255
commit 6cc66197ff
1 changed files with 24 additions and 21 deletions
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45
src/backend/access/transam/xlogfuncs.c
View File

@ -45,6 +45,9 @@
static BackupState *backup_state = NULL; static BackupState *backup_state = NULL;
static StringInfo tablespace_map = NULL; static StringInfo tablespace_map = NULL;
/* Session-level context for the SQL-callable backup functions */
static MemoryContext backupcontext = NULL;
/* /*
* pg_backup_start: set up for taking an on-line backup dump * pg_backup_start: set up for taking an on-line backup dump
* *
@ -72,27 +75,26 @@ pg_backup_start(PG_FUNCTION_ARGS)
/* /*
* backup_state and tablespace_map need to be long-lived as they are used * backup_state and tablespace_map need to be long-lived as they are used
* in pg_backup_stop(). * in pg_backup_stop(). These are allocated in a dedicated memory context
* child of TopMemoryContext, deleted at the end of pg_backup_stop(). If
* an error happens before ending the backup, memory would be leaked in
* this context until pg_backup_start() is called again.
*/ */
oldcontext = MemoryContextSwitchTo(TopMemoryContext); if (backupcontext == NULL)
/* Allocate backup state or reset it, if it comes from a previous run */
if (backup_state == NULL)
backup_state = (BackupState *) palloc0(sizeof(BackupState));
else
MemSet(backup_state, 0, sizeof(BackupState));
/*
* tablespace_map may have been created in a previous backup, so take this
* occasion to clean it.
*/
if (tablespace_map != NULL)
{ {
pfree(tablespace_map->data); backupcontext = AllocSetContextCreate(TopMemoryContext,
pfree(tablespace_map); "on-line backup context",
ALLOCSET_START_SMALL_SIZES);
}
else
{
backup_state = NULL;
tablespace_map = NULL; tablespace_map = NULL;
MemoryContextReset(backupcontext);
} }
oldcontext = MemoryContextSwitchTo(backupcontext);
backup_state = (BackupState *) palloc0(sizeof(BackupState));
tablespace_map = makeStringInfo(); tablespace_map = makeStringInfo();
MemoryContextSwitchTo(oldcontext); MemoryContextSwitchTo(oldcontext);
@ -157,13 +159,14 @@ pg_backup_stop(PG_FUNCTION_ARGS)
values[2] = CStringGetTextDatum(tablespace_map->data); values[2] = CStringGetTextDatum(tablespace_map->data);
/* Deallocate backup-related variables */ /* Deallocate backup-related variables */
pfree(backup_state);
backup_state = NULL;
pfree(tablespace_map->data);
pfree(tablespace_map);
tablespace_map = NULL;
pfree(backup_label); pfree(backup_label);
/* Clean up the session-level state and its memory context */
backup_state = NULL;
tablespace_map = NULL;
MemoryContextDelete(backupcontext);
backupcontext = NULL;
/* Returns the record as Datum */ /* Returns the record as Datum */
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls))); PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
} }