Re: [HACKERS] like/ilike improvements

Andrew Dunstan <andrew@dunslane.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