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

tglsfdc · tglsfdc · commit babe545caeba · 2021-12-01T13:44:46.000-05:00
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 3aafc03, 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
diff --git 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();
 		}
