From: John Naylor <john.naylor@postgresql.org>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Speed up tail processing when hashing aligned C strings, take tw
Date: Sat, 06 Apr 2024 10:17:15 +0000
Message-ID: <E1rt36p-000nMe-Cc@gemulon.postgresql.org> (raw)
Speed up tail processing when hashing aligned C strings, take two
After encountering the NUL terminator, the word-at-a-time loop exits
and we must hash the remaining bytes. Previously we calculated
the terminator's position and re-loaded the remaining bytes from
the input string. This was slower than the unaligned case for very
short strings. We already have all the data we need in a register,
so let's just mask off the bytes we need and hash them immediately.
In addition to endianness issues, the previous attempt upset valgrind
in the way it computed the mask. Whether by accident or by wisdom,
the author's proposed method passes locally with valgrind 3.22.
Ants Aasma, with cosmetic adjustments by me
Discussion: https://postgr.es/m/CANwKhkP7pCiW_5fAswLhs71-JKGEz1c1%2BPC0a_w1fwY4iGMqUA%40mail.gmail.com
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/a365d9e2e8c1ead27203a4431211098292777d3b
Modified Files
--------------
src/include/common/hashfn_unstable.h | 46 ++++++++++++++++++++++++++++--------
1 file changed, 36 insertions(+), 10 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: john.naylor@postgresql.org, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Speed up tail processing when hashing aligned C strings, take tw
In-Reply-To: <E1rt36p-000nMe-Cc@gemulon.postgresql.org>
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