Replace CLOBBER_CACHE_ALWAYS with run-time GUC

Forced cache invalidation (CLOBBER_CACHE_ALWAYS) has been impractical
to use for testing in PostgreSQL because it's so slow and because it's
toggled on/off only at build time.  It is helpful when hunting bugs in
any code that uses the sycache/relcache because causes cache
invalidations to be injected whenever it would be possible for an
invalidation to occur, whether or not one was really pending.

Address this by providing run-time control over cache clobber
behaviour using the new debug_invalidate_system_caches_always GUC.
Support is not compiled in at all unless assertions are enabled or
CLOBBER_CACHE_ENABLED is explicitly defined at compile time.  It
defaults to 0 if compiled in, so it has negligible effect on assert
build performance by default.

When support is compiled in, test code can now set
debug_invalidate_system_caches_always=1 locally to a backend to test
specific queries, functions, extensions, etc.  Or tests can toggle it
globally for a specific test case while retaining normal performance
during test setup and teardown.

For backwards compatibility with existing test harnesses and scripts,
debug_invalidate_system_caches_always defaults to 1 if
CLOBBER_CACHE_ALWAYS is defined, and to 3 if CLOBBER_CACHE_RECURSIVE
is defined.

CLOBBER_CACHE_ENABLED is now visible in pg_config_manual.h, as is the
related RECOVER_RELATION_BUILD_MEMORY setting for the relcache.

Author: Craig Ringer <craig.ringer@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/CAMsr+YF=+ctXBZj3ywmvKNUjWpxmuTuUKuv-rgbHGX5i5pLstQ@mail.gmail.com

1 files changed, 40 insertions, 27 deletions

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index afc3451a543..7ef510cd01b 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -91,15 +91,15 @@
 #define RELCACHE_INIT_FILEMAGIC		0x573266	/* version ID value */
 
 /*
- * Default policy for whether to apply RECOVER_RELATION_BUILD_MEMORY:
- * do so in clobber-cache builds but not otherwise.  This choice can be
- * overridden at compile time with -DRECOVER_RELATION_BUILD_MEMORY=1 or =0.
+ * Whether to bother checking if relation cache memory needs to be freed
+ * eagerly.  See also RelationBuildDesc() and pg_config_manual.h.
  */
-#ifndef RECOVER_RELATION_BUILD_MEMORY
-#if defined(CLOBBER_CACHE_ALWAYS) || defined(CLOBBER_CACHE_RECURSIVELY)
-#define RECOVER_RELATION_BUILD_MEMORY 1
+#if defined(RECOVER_RELATION_BUILD_MEMORY) && (RECOVER_RELATION_BUILD_MEMORY != 0)
+#define MAYBE_RECOVER_RELATION_BUILD_MEMORY 1
 #else
 #define RECOVER_RELATION_BUILD_MEMORY 0
+#ifdef CLOBBER_CACHE_ENABLED
+#define MAYBE_RECOVER_RELATION_BUILD_MEMORY 1
 #endif
 #endif
 
@@ -1040,19 +1040,25 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 	 * scope, and relcache loads shouldn't happen so often that it's essential
 	 * to recover transient data before end of statement/transaction.  However
 	 * that's definitely not true in clobber-cache test builds, and perhaps
-	 * it's not true in other cases.  If RECOVER_RELATION_BUILD_MEMORY is not
-	 * zero, arrange to allocate the junk in a temporary context that we'll
-	 * free before returning.  Make it a child of caller's context so that it
-	 * will get cleaned up appropriately if we error out partway through.
+	 * it's not true in other cases.
+	 *
+	 * When cache clobbering is enabled or when forced to by
+	 * RECOVER_RELATION_BUILD_MEMORY=1, arrange to allocate the junk in a
+	 * temporary context that we'll free before returning.  Make it a child
+	 * of caller's context so that it will get cleaned up appropriately if
+	 * we error out partway through.
 	 */
-#if RECOVER_RELATION_BUILD_MEMORY
-	MemoryContext tmpcxt;
-	MemoryContext oldcxt;
+#ifdef MAYBE_RECOVER_RELATION_BUILD_MEMORY
+	MemoryContext tmpcxt = NULL;
+	MemoryContext oldcxt = NULL;
 
-	tmpcxt = AllocSetContextCreate(CurrentMemoryContext,
-								   "RelationBuildDesc workspace",
-								   ALLOCSET_DEFAULT_SIZES);
-	oldcxt = MemoryContextSwitchTo(tmpcxt);
+	if (RECOVER_RELATION_BUILD_MEMORY || debug_invalidate_system_caches_always > 0)
+	{
+		tmpcxt = AllocSetContextCreate(CurrentMemoryContext,
+									   "RelationBuildDesc workspace",
+									   ALLOCSET_DEFAULT_SIZES);
+		oldcxt = MemoryContextSwitchTo(tmpcxt);
+	}
 #endif
 
 	/*
@@ -1065,10 +1071,13 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 	 */
 	if (!HeapTupleIsValid(pg_class_tuple))
 	{
-#if RECOVER_RELATION_BUILD_MEMORY
-		/* Return to caller's context, and blow away the temporary context */
-		MemoryContextSwitchTo(oldcxt);
-		MemoryContextDelete(tmpcxt);
+#ifdef MAYBE_RECOVER_RELATION_BUILD_MEMORY
+		if (tmpcxt)
+		{
+			/* Return to caller's context, and blow away the temporary context */
+			MemoryContextSwitchTo(oldcxt);
+			MemoryContextDelete(tmpcxt);
+		}
 #endif
 		return NULL;
 	}
@@ -1247,10 +1256,13 @@ RelationBuildDesc(Oid targetRelId, bool insertIt)
 	/* It's fully valid */
 	relation->rd_isvalid = true;
 
-#if RECOVER_RELATION_BUILD_MEMORY
-	/* Return to caller's context, and blow away the temporary context */
-	MemoryContextSwitchTo(oldcxt);
-	MemoryContextDelete(tmpcxt);
+#ifdef MAYBE_RECOVER_RELATION_BUILD_MEMORY
+	if (tmpcxt)
+	{
+		/* Return to caller's context, and blow away the temporary context */
+		MemoryContextSwitchTo(oldcxt);
+		MemoryContextDelete(tmpcxt);
+	}
 #endif
 
 	return relation;
@@ -1646,8 +1658,9 @@ LookupOpclassInfo(Oid operatorClassOid,
 	 * while we are loading the info, and it's very hard to provoke that if
 	 * this happens only once per opclass per backend.
 	 */
-#if defined(CLOBBER_CACHE_ALWAYS)
-	opcentry->valid = false;
+#ifdef CLOBBER_CACHE_ENABLED
+	if (debug_invalidate_system_caches_always > 0)
+		opcentry->valid = false;
 #endif
 
 	if (opcentry->valid)