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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2017-05-12 18:30:02 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2017-05-12 18:30:17 -0400 |
| commit | 8085a4f7510191b8fe7f8f7b5846fdbc79abcf8d (patch) | |
| tree | 99525de1d41451aa7b492e4b19c1f95d00f2f2f1 | |
| parent | 5e2af609e14ede1b5e0d73d59ed8548c76e1943a (diff) | |
| download | postgresql-8085a4f7510191b8fe7f8f7b5846fdbc79abcf8d.tar.gz postgresql-8085a4f7510191b8fe7f8f7b5846fdbc79abcf8d.zip | |
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=Rg@mail.gmail.com
| -rw-r--r-- | src/backend/utils/cache/relfilenodemap.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/backend/utils/cache/relfilenodemap.c b/src/backend/utils/cache/relfilenodemap.c index c790309caae..612f0f3a0d1 100644 --- a/src/backend/utils/cache/relfilenodemap.c +++ b/src/backend/utils/cache/relfilenodemap.c @@ -123,7 +123,7 @@ InitializeRelfilenodeMap(void) * error. */ RelfilenodeMapHash = - hash_create("RelfilenodeMap cache", 1024, &ctl, + hash_create("RelfilenodeMap cache", 64, &ctl, HASH_ELEM | HASH_BLOBS | HASH_CONTEXT); /* Watch for invalidation events. */ |