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Commit854ae8c

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Fix permanent memory leak in autovacuum launcher
get_database_list was uselessly allocating its output data, along somecreated along the way, in a permanent memory context. This didn'tmatter when autovacuum was a single, short-lived process, but now thatthe launcher is permanent, it shows up as a permanent leak.To fix, make get_database list allocate its output data in the caller'scontext, which is in charge of freeing it when appropriate; and thememory leaked by heap_beginscan et al is allocated in a throwawaytransaction context.
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‎src/backend/postmaster/autovacuum.c‎

Lines changed: 17 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1754,6 +1754,9 @@ autovac_balance_cost(void)
17541754
* get_database_list
17551755
*Return a list of all databases found in pg_database.
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*
1757+
* The list and associated data is allocated in the caller's memory context,
1758+
* which is in charge of ensuring that it's properly cleaned up afterwards.
1759+
*
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* Note: this is the only function in which the autovacuum launcher uses a
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* transaction. Although we aren't attached to any particular database and
17591762
* therefore can't access most catalogs, we do have enough infrastructure
@@ -1766,6 +1769,10 @@ get_database_list(void)
17661769
Relationrel;
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HeapScanDescscan;
17681771
HeapTupletup;
1772+
MemoryContextresultcxt;
1773+
1774+
/* This is the context that we will allocate our output data in */
1775+
resultcxt=CurrentMemoryContext;
17691776

17701777
/*
17711778
* Start a transaction so we can access pg_database, and get a snapshot.
@@ -1777,16 +1784,22 @@ get_database_list(void)
17771784
StartTransactionCommand();
17781785
(void)GetTransactionSnapshot();
17791786

1780-
/* Allocate our results in AutovacMemCxt, not transaction context */
1781-
MemoryContextSwitchTo(AutovacMemCxt);
1782-
17831787
rel=heap_open(DatabaseRelationId,AccessShareLock);
17841788
scan=heap_beginscan(rel,SnapshotNow,0,NULL);
17851789

17861790
while (HeapTupleIsValid(tup=heap_getnext(scan,ForwardScanDirection)))
17871791
{
17881792
Form_pg_databasepgdatabase= (Form_pg_database)GETSTRUCT(tup);
17891793
avw_dbase*avdb;
1794+
MemoryContextoldcxt;
1795+
1796+
/*
1797+
* Allocate our results in the caller's context, not the transaction's.
1798+
* We do this inside the loop, and restore the original context at the
1799+
* end, so that leaky things like heap_getnext() are not called in a
1800+
* potentially long-lived context.
1801+
*/
1802+
oldcxt=MemoryContextSwitchTo(resultcxt);
17901803

17911804
avdb= (avw_dbase*)palloc(sizeof(avw_dbase));
17921805

@@ -1797,6 +1810,7 @@ get_database_list(void)
17971810
avdb->adw_entry=NULL;
17981811

17991812
dblist=lappend(dblist,avdb);
1813+
MemoryContextSwitchTo(oldcxt);
18001814
}
18011815

18021816
heap_endscan(scan);

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