From 89d41607292cd2430bffb258ab42cd7045335ded Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Mon, 18 Oct 2021 13:59:11 +0300 Subject: [PATCH v10 3/3] Optimize hash function --- src/backend/utils/resowner/resowner.c | 24 ++++++++++++++++++------ src/include/common/hashfn.h | 15 +++++++++++++++ 2 files changed, 33 insertions(+), 6 deletions(-) diff --git a/src/backend/utils/resowner/resowner.c b/src/backend/utils/resowner/resowner.c index 35e824d4534..118bd2b34c9 100644 --- a/src/backend/utils/resowner/resowner.c +++ b/src/backend/utils/resowner/resowner.c @@ -169,15 +169,27 @@ static void ReleaseAuxProcessResourcesCallback(int code, Datum arg); * INTERNAL ROUTINES * *****************************************************************************/ +/* + * Hash function for value+kind combination. + */ static inline uint32 hash_resource_elem(Datum value, ResourceOwnerFuncs *kind) { - Datum data[2]; - - data[0] = value; - data[1] = PointerGetDatum(kind); - - return hash_bytes((unsigned char *) &data, 2 * SIZEOF_DATUM); + /* + * Most resources types store a pointer in 'value', and pointers are + * unique all on their own. But some resources store plain integers + * (Files and Buffers as of this writing), so we want to incorporate the + * 'kind' in the hash too, otherwise those resources will collide a lot. + * But because there are only a few resource kinds like that - and only a + * few resource kinds to begin with - we don't need to work too hard to + * mix 'kind' into the hash. Just add it with hash_combine(), it perturbs + * the result enough for our purposes. + */ +#if SIZEOF_DATUM == 8 + return hash_combine64(murmurhash64((uint64) value), (uint64) kind); +#else + return hash_combine(murmurhash32((uint32) value), (uint32) kind); +#endif } /* diff --git a/src/include/common/hashfn.h b/src/include/common/hashfn.h index c634cc067a1..009ffbbdd38 100644 --- a/src/include/common/hashfn.h +++ b/src/include/common/hashfn.h @@ -101,4 +101,19 @@ murmurhash32(uint32 data) return h; } +/* 64-bit variant */ +static inline uint64 +murmurhash64(uint64 data) +{ + uint64 h = data; + + h ^= h >> 33; + h *= 0xff51afd7ed558ccd; + h ^= h >> 33; + h *= 0xc4ceb9fe1a85ec53; + h ^= h >> 33; + + return h; +} + #endif /* HASHFN_H */ -- 2.30.2