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, 39 insertions, 0 deletions

diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 3cbdc6d180..d27c8601fa 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -310,6 +310,45 @@
 /* #define RANDOMIZE_ALLOCATED_MEMORY */
 
 /*
+ * For cache invalidation debugging, define CLOBBER_CACHE_ENABLED to enable
+ * use of the debug_invalidate_system_caches_always GUC to aggressively flush
+ * syscache/relcache entries whenever it's possible to deliver invalidations.
+ * See AcceptInvalidationMessages() in src/backend/utils/cache/inval.c for
+ * details.
+ *
+ * USE_ASSERT_CHECKING builds default to enabling this.  It's possible to use
+ * CLOBBER_CACHE_ENABLED without a cassert build and the implied
+ * CLOBBER_FREED_MEMORY and MEMORY_CONTEXT_CHECKING options but it's unlikely
+ * to be as effective at identifying problems.
+ */
+/* #define CLOBBER_CACHE_ENABLED */
+
+#if defined(USE_ASSERT_CHECKING) && !defined(CLOBBER_CACHE_ENABLED)
+#define CLOBBER_CACHE_ENABLED
+#endif
+
+/*
+ * Backwards compatibility for the older compile-time-only cache clobber
+ * macros.
+ */
+#if !defined(CLOBBER_CACHE_ENABLED) && (defined(CLOBBER_CACHE_ALWAYS) || defined(CLOBBER_CACHE_RECURSIVELY))
+#define CLOBBER_CACHE_ENABLED
+#endif
+
+/*
+ * Recover memory used for relcache entries when invalidated.  See
+ * RelationBuildDescr() in src/backend/utils/cache/relcache.c.
+ *
+ * This is active automatically for clobber cache builds when clobbering is
+ * active, but can be overridden here by explicitly defining
+ * RECOVER_RELATION_BUILD_MEMORY.  Define to 1 to always free relation cache
+ * memory even when clobber is off, or to 0 to never free relation cache
+ * memory even when clobbering is on.
+ */
+/* #define RECOVER_RELATION_BUILD_MEMORY 0 */ /* Force disable */
+/* #define RECOVER_RELATION_BUILD_MEMORY 1 */ /* Force enable */
+
+/*
  * Define this to force all parse and plan trees to be passed through
  * copyObject(), to facilitate catching errors and omissions in
  * copyObject().