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Avoid leaking memory during large-scale REASSIGN OWNED BY operations.

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The various ALTER OWNER routines tend to leak memory in
CurrentMemoryContext.  That's not a problem when they're only called
once per command; but in this usage where we might be touching many
objects, it can amount to a serious memory leak.  Fix that by running
each call in a short-lived context.

(DROP OWNED BY likely has a similar issue, except that you'll probably
run out of lock table space before noticing.  REASSIGN is worth fixing
since for most non-table object types, it won't take any lock.)

Back-patch to all supported branches.  Unfortunately, in the back
branches this helps to only a limited extent, since the sinval message
queue bloats quite a lot in this usage before commit 3aafc030a,
consuming memory more or less comparable to what's actually leaked.
Still, it's clearly a leak with a simple fix, so we might as well fix it.

Justin Pryzby, per report from Guillaume Lelarge

Discussion: https://postgr.es/m/CAECtzeW2DAoioEGBRjR=CzHP6TdL=yosGku8qZxfX9hhtrBB0Q@mail.gmail.com
This commit is contained in:
Tom Lane 2021-12-01 13:44:47 -05:00
parent 4b8eec716a
commit 8f4b0200e1
1 changed files with 20 additions and 0 deletions
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20
src/backend/catalog/pg_shdepend.c
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@ -65,6 +65,7 @@
#include "storage/lmgr.h"
#include "utils/acl.h"
#include "utils/fmgroids.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
typedef enum
@ -1549,6 +1550,8 @@ shdepReassignOwned(List *roleids, Oid newrole)
while ((tuple = systable_getnext(scan)) != NULL)
{
Form_pg_shdepend sdepForm = (Form_pg_shdepend) GETSTRUCT(tuple);
MemoryContext cxt,
oldcxt;
/*
* We only operate on shared objects and objects in the current
@ -1566,6 +1569,18 @@ shdepReassignOwned(List *roleids, Oid newrole)
if (sdepForm->deptype != SHARED_DEPENDENCY_OWNER)
continue;
/*
* The various ALTER OWNER routines tend to leak memory in
* CurrentMemoryContext. That's not a problem when they're only
* called once per command; but in this usage where we might be
* touching many objects, it can amount to a serious memory leak.
* Fix that by running each call in a short-lived context.
*/
cxt = AllocSetContextCreate(CurrentMemoryContext,
"shdepReassignOwned",
ALLOCSET_DEFAULT_SIZES);
oldcxt = MemoryContextSwitchTo(cxt);
/* Issue the appropriate ALTER OWNER call */
switch (sdepForm->classid)
{
@ -1654,6 +1669,11 @@ shdepReassignOwned(List *roleids, Oid newrole)
elog(ERROR, "unexpected classid %u", sdepForm->classid);
break;
}
/* Clean up */
MemoryContextSwitchTo(oldcxt);
MemoryContextDelete(cxt);
/* Make sure the next iteration will see my changes */
CommandCounterIncrement();
}