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

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

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();
                }