Improve sys/catcache performance.
The following are the individual improvements:
1) Avoidance of FunctionCallInfo based function calls, replaced by more efficient functions with a native C argument
interface.
2) Don't extract columns from a cache entry's tuple whenever matching entries - instead store them as a Datum array.
Thisalso allows to get rid of having to build dummy tuples for negative & list entries, and of a hack for dealing
withcstring vs. text weirdness.
3) Reorder members of catcache.h struct, so imortant entries are more likely to be on one cacheline.
4) Allowing the compiler to specialize critical SearchCatCache for a specific number of attributes allows to unroll
loopsand avoid other nkeys dependant initialization.
5) Only initializing the ScanKey when necessary, i.e. catcache misses, greatly reduces cache unnecessary cpu cache
misses.
6) Split of the cache-miss case from the hash lookup, reducing stack allocations etc in the common case.
7) CatCTup and their corresponding heaptuple are allocated in one piece.
This results in making cache lookups themselves roughly three times as
fast - full-system benchmarks obviously improve less than that.
I've also evaluated further techniques:
- replace open coded hash with simplehash - the list walk right now shows up in profiles. Unfortunately it's not easy
todo so safely as an entry's memory location can change at various times, which doesn't work well with the refcounting
andcache invalidation.
- Cacheline-aligning CatCTup entries - helps some with performance, but the win isn't big and the code for it is ugly,
becausethe tuples have to be freed as well.
- add more proper functions, rather than macros for SearchSysCacheCopyN etc., but right now they don't show up in
profiles.
The reason the macro wrapper for syscache.c/h have to be changed,
rather than just catcache, is that doing otherwise would require
exposing the SysCache array to the outside. That might be a good idea
anyway, but it's for another day.
Author: Andres Freund
Reviewed-By: Robert Haas
Discussion: https://postgr.es/m/20170914061207.zxotvyopetm7lrrp@alap3.anarazel.de
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/141fd1b66ce6e3d10518d66d4008bd368f1505fd
Modified Files
--------------
src/backend/utils/cache/catcache.c | 692 +++++++++++++++++++++++++------------
src/backend/utils/cache/syscache.c | 49 ++-
src/include/utils/catcache.h | 122 ++++---
src/include/utils/syscache.h | 23 +-
src/tools/pgindent/typedefs.list | 2 +
5 files changed, 608 insertions(+), 280 deletions(-)
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