Limit depth of forced recursion for CLOBBER_CACHE_RECURSIVELY.

It's somewhat surprising that we got away with this before.  (Actually,
since nobody tests this routinely AFAIK, it might've been broken for
awhile.  But it's definitely broken in the wake of commit f868a8143.)
It seems sufficient to limit the forced recursion to a small number
of levels.

Back-patch to all supported branches, like the preceding patch.

Discussion: https://postgr.es/m/12259.1532117714@sss.pgh.pa.us

diff --git a/src/backend/utils/cache/inval.c b/src/backend/utils/cache/inval.c
index 16d86a29390edb0aeec056a5373ebb006e6eab39..f3ded4def90253c2c4ab1c345b12939608af7467 100644 (file)
--- a/src/backend/utils/cache/inval.c
+++ b/src/backend/utils/cache/inval.c
@@ -708,7 +708,17 @@ AcceptInvalidationMessages(void)
                }
        }
 #elif defined(CLOBBER_CACHE_RECURSIVELY)
-       InvalidateSystemCaches();
+       {
+               static int      recursion_depth = 0;
+
+               /* Maximum depth is arbitrary depending on your threshold of pain */
+               if (recursion_depth < 3)
+               {
+                       recursion_depth++;
+                       InvalidateSystemCaches();
+                       recursion_depth--;
+               }
+       }
 #endif
 }