Use the typcache to cache constraints for domain types

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 1 March 2015 13:06 UTC

Previously, we cached domain constraints for the life of a query, or really for the life of the FmgrInfo struct that was used to invoke domain_in() or domain_check(). But plpgsql (and probably other places) are set up to cache such FmgrInfos for the whole lifespan of a session, which meant they could be enforcing really stale sets of constraints. On the other hand, searching pg_constraint once per query gets kind of expensive too: testing says that as much as half the runtime of a trivial query such as "SELECT 0::domaintype" went into that.

To fix this, delegate the responsibility for tracking a domain's constraints to the typcache, which has the infrastructure needed to detect syscache invalidation events that signal possible changes. This not only removes unnecessary repeat reads of pg_constraint, but ensures that we never apply stale constraint data: whatever we use is the current data according to syscache rules.

Unfortunately, the current configuration of the system catalogs means we have to flush cached domain-constraint data whenever either pg_type or pg_constraint changes, which happens rather a lot (eg, creation or deletion of a temp table will do it). It might be worth rearranging things to split pg_constraint into two catalogs, of which the domain constraint one would probably be very low-traffic. That's a job for another patch though, and in any case this patch should improve matters materially even with that handicap.

This patch makes use of the recently-added memory context reset callback feature to manage the lifespan of domain constraint caches, so that we don't risk deleting a cache that might be in the midst of evaluation.

Although this is a bug fix as well as a performance improvement, no back-patch. There haven't been many if any field complaints about stale domain constraint checks, so it doesn't seem worth taking the risk of modifying data structures as basic as MemoryContexts in back branches.

8abb3cd Use the typcache to cache constraints for domain types.
src/backend/commands/tablecmds.c | 4 +-
src/backend/commands/typecmds.c | 127 -----------
src/backend/executor/execQual.c | 13 +-
src/backend/utils/adt/domains.c | 78 +++----
src/backend/utils/cache/typcache.c | 405 +++++++++++++++++++++++++++++++++-
src/include/commands/typecmds.h | 2 -
src/include/nodes/execnodes.h | 5 +-
src/include/utils/typcache.h | 37 ++++
src/test/regress/expected/domain.out | 30 +++
src/test/regress/sql/domain.sql | 27 +++
10 files changed, 547 insertions(+), 181 deletions(-)

Upstream: git.postgresql.org

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