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Re: [HACKERS] like/ilike improvements

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>
Cc: ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, "Patches (PostgreSQL)" <pgsql-patches(at)postgresql(dot)org>
Subject: Re: [HACKERS] like/ilike improvements
Date: 2007-06-01 22:58:18
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Lists: pgsql-hackerspgsql-patches
Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> ITAGAKI Takahiro wrote:
>>         | SQL_ASCII | LATIN1 |  UTF8 | EUC_JP 
>> ---------+-----------+--------+-------+---------
>> HEAD    |      8017 |   8029 | 16928 |  18213 
>> Patched |      7899 |   7887 |  9985 |  10370 [ms]
>> It improved the performance not only for UTF8, but also for other
>> multi-byte encodings and a bit for single-byte encodings.

> Interesting. I infer from these results that the biggest bang here comes 
> from abandoning CHAREQ and doing all comparisons byte-wise.

It looks like CHAREQ and NextChar are both pretty expensive, no doubt
due to having to drill down through the MB encoding vectoring mechanism
to find out what to do.

A technique we might want to apply in future patches is to have an API
whereby we can get a direct function pointer to the appropriate mblen
or other encoding-dependent function, and then call directly to the
right place in the inner loops instead of having to go through the
intermediate vectoring function every time.

			regards, tom lane

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