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

Wed, 1 Dec 2021 18:44:46 +0000 (13:44 -0500)

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

src/backend/catalog/pg_shdepend.c patch | blob | blame | history

diff --git a/src/backend/catalog/pg_shdepend.c b/src/backend/catalog/pg_shdepend.c

index 9ea42f805fad503245f317dafedcc57cbbfcdd5d..c20b1fbb9618c7632af1be87473e5983a2566da6 100644 (file)

--- a/src/backend/catalog/pg_shdepend.c

+++ b/src/backend/catalog/pg_shdepend.c

@@ -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

@@ -1497,6 +1498,8 @@ 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

@@ -1510,6 +1513,18 @@ 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)

{

@@ -1598,6 +1613,11 @@ 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();

}

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