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, 24 insertions, 0 deletions

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 383b7d0d710..1ccf7593eea 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -99,6 +99,7 @@
 #include "utils/rls.h"
 #include "utils/snapmgr.h"
 #include "utils/tzparser.h"
+#include "utils/inval.h"
 #include "utils/varlena.h"
 #include "utils/xml.h"
 
@@ -3402,6 +3403,29 @@ static struct config_int ConfigureNamesInt[] =
 		check_huge_page_size, NULL, NULL
 	},
 
+	{
+		{"debug_invalidate_system_caches_always", PGC_SUSET, DEVELOPER_OPTIONS,
+			gettext_noop("Aggressively invalidate system caches for debugging purposes."),
+			NULL,
+			GUC_NOT_IN_SAMPLE
+		},
+		&debug_invalidate_system_caches_always,
+#ifdef CLOBBER_CACHE_ENABLED
+		/* Set default based on older compile-time-only cache clobber macros */
+#if defined(CLOBBER_CACHE_RECURSIVELY)
+		3,
+#elif defined(CLOBBER_CACHE_ALWAYS)
+		1,
+#else
+		0,
+#endif
+		0, 5,
+#else	/* not CLOBBER_CACHE_ENABLED */
+		0, 0, 0,
+#endif	/* not CLOBBER_CACHE_ENABLED */
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, 0, 0, NULL, NULL, NULL