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Simplify abbreviated key hashing during cardinality estimation

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In the wake of commit 2a600a93c, Datums are 64-bit values, so
we no longer need to fold the abbreviated key to 32 bits before
hashing. Instead, use murmurhash64(), which is simpler and avoids
a function call. Also replace hash_uint32() with murmurhash32()
in related places.

Author: Aleksander Alekseev <aleksander@tigerdata.com>
Suggested-by: John Naylor <johncnaylorls@gmail.com>
Reviewed-by: Aditya Gollamudi <adigollamudi@gmail.com> (earlier version)
Reviewed-by: Michael Paquier <michael@paquier.xyz> (earlier version)
Discussion: https://postgr.es/m/CAJ7c6TMPhDRQMmkUHPv8oOK97B1mR8NRS61DgjpdaZUPAwaeZQ%40mail.gmail.com
This commit is contained in:
John Naylor
2026-09-21 17:36:50 +07:00
parent 9e17d25e79
commit d39fda1cc4
5 changed files with 10 additions and 34 deletions
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9
src/backend/utils/adt/bytea.c
View File

@@ -1110,17 +1110,12 @@ bytea_abbrev_convert(Datum original, SortSupport ssup)
Min(len, PG_CACHE_LINE_SIZE)));
if (len > PG_CACHE_LINE_SIZE)
hash ^= DatumGetUInt32(hash_uint32((uint32) len));
hash ^= murmurhash32((uint32) len);
addHyperLogLog(&bss->full_card, hash);
/* Hash abbreviated key */
{
uint32 tmp;
tmp = DatumGetUInt32(res) ^ (uint32) (DatumGetUInt64(res) >> 32);
hash = DatumGetUInt32(hash_uint32(tmp));
}
hash = (uint32) murmurhash64(DatumGetUInt64(res));
addHyperLogLog(&bss->abbr_card, hash);

9
src/backend/utils/adt/network.c
View File

@@ -738,13 +738,8 @@ network_abbrev_convert(Datum original, SortSupport ssup)
/* Hash abbreviated key */
if (uss->estimating)
{
uint32 tmp;
tmp = DatumGetUInt32(res) ^ (uint32) (DatumGetUInt64(res) >> 32);
addHyperLogLog(&uss->abbr_card, DatumGetUInt32(hash_uint32(tmp)));
}
addHyperLogLog(&uss->abbr_card,
(uint32) murmurhash64(DatumGetUInt64(res)));
return res;
}

8
src/backend/utils/adt/numeric.c
View File

@@ -2404,12 +2404,8 @@ numeric_abbrev_convert_var(const NumericVar *var, NumericSortSupport *nss)
result = -result;
if (nss->estimating)
{
uint32 tmp = ((uint32) result
^ (uint32) ((uint64) result >> 32));
addHyperLogLog(&nss->abbr_card, DatumGetUInt32(hash_uint32(tmp)));
}
addHyperLogLog(&nss->abbr_card,
(uint32) murmurhash64((uint64) result));
return NumericAbbrevGetDatum(result);
}

9
src/backend/utils/adt/uuid.c
View File

@@ -521,13 +521,8 @@ uuid_abbrev_convert(Datum original, SortSupport ssup)
uss->input_count += 1;
if (uss->estimating)
{
uint32 tmp;
tmp = DatumGetUInt32(res) ^ (uint32) (DatumGetUInt64(res) >> 32);
addHyperLogLog(&uss->abbr_card, DatumGetUInt32(hash_uint32(tmp)));
}
addHyperLogLog(&uss->abbr_card,
(uint32) murmurhash64(DatumGetUInt64(res)));
/*
* Byteswap on little-endian machines.

9
src/backend/utils/adt/varlena.c
View File

@@ -2158,17 +2158,12 @@ varstr_abbrev_convert(Datum original, SortSupport ssup)
Min(len, PG_CACHE_LINE_SIZE)));
if (len > PG_CACHE_LINE_SIZE)
hash ^= DatumGetUInt32(hash_uint32((uint32) len));
hash ^= murmurhash32((uint32) len);
addHyperLogLog(&sss->full_card, hash);
/* Hash abbreviated key */
{
uint32 tmp;
tmp = DatumGetUInt32(res) ^ (uint32) (DatumGetUInt64(res) >> 32);
hash = DatumGetUInt32(hash_uint32(tmp));
}
hash = (uint32) murmurhash64(DatumGetUInt64(res));
addHyperLogLog(&sss->abbr_card, hash);