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 Discussion: https://www.postgresql.org/message-id/flat/CAMsr+YF=+ctXBZj3ywmvKNUjWpxmuTuUKuv-rgbHGX5i5pLstQ@mail.gmail.com
4656e3d668 Replace CLOBBER_CACHE_ALWAYS with run-time GUC
doc/src/sgml/config.sgml | 37 ++++++++++++++++++++
doc/src/sgml/regress.sgml | 3 +-
src/backend/utils/adt/lockfuncs.c | 2 +-
src/backend/utils/cache/inval.c | 48 +++++++++++++-------------
src/backend/utils/cache/plancache.c | 2 +-
src/backend/utils/cache/relcache.c | 67 ++++++++++++++++++++++---------------
src/backend/utils/misc/guc.c | 24 +++++++++++++
src/include/pg_config_manual.h | 39 +++++++++++++++++++++
src/include/utils/inval.h | 1 +
9 files changed, 169 insertions(+), 54 deletions(-)