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help / color / mirror / Atom feedFrom: Heikki Linnakangas <[email protected]>
Subject: [PATCH v10 3/3] Optimize hash function
Date: Mon, 18 Oct 2021 13:59:11 +0300
---
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
--------------AF226508B1039DE40796DE51--
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