Reduce initial size of RelfilenodeMapHash. A test case provided by Mathieu Fenniak shows that hash_seq_search'ing this hashtable can consume a very significant amount of overhead during logical decoding, which triggers frequent cache invalidation. Testing suggests that the actual population of the hashtable is often no more than a few dozen entries, so we can cut the overhead just by dropping the initial number of buckets down from 1024 --- I chose to cut it to 64. (In situations where we do have a significant number of entries, we shouldn't get any real penalty from doing this, as the dynahash.c code will resize the hashtable automatically.)
This gives a further factor-of-two savings in Mathieu's test case. That may be overly optimistic for real-world benefit, as real cases may have larger average table populations, but it's hard to see it turning into a net negative for any workload. Back-patch to 9.4 where relfilenodemap.c was introduced. Discussion: https://postgr.es/m/CAHoiPjzea6N0zuCi=+f9v_j94nfsy6y8SU7-=bp4=7qw6_i=r...@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/8085a4f7510191b8fe7f8f7b5846fdbc79abcf8d Modified Files -------------- src/backend/utils/cache/relfilenodemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers
