From: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> |
---|---|
To: | "Andrew Dunstan" <andrew(at)dunslane(dot)net> |
Cc: | <pgsql-patches(at)postgresql(dot)org> |
Subject: | Re: CopyReadLineText optimization |
Date: | 2008-03-06 20:08:03 |
Message-ID: | 47D04F23.8060908@enterprisedb.com |
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Lists: | pgsql-hackers pgsql-patches |
Andrew Dunstan wrote:
> Heikki Linnakangas wrote:
>> Andrew Dunstan wrote:
>>> I'm still a bit worried about applying it unless it gets some
>>> adaptive behaviour or something so that we don't cause any serious
>>> performance regressions in some cases.
>>
>> I'll try to come up with something. At the most conservative end, we
>> could fall back to the current method on the first escape, quote or
>> backslash character.
>
> That's far too conservative, I think. Somewhere a bit short of your
> observed breakeven point seems about right.
The problem is, you don't know how many "stop" characters there is until
you've counted them.
We could fall back after X such characters, or only start using memchr
after seeing 8 consecutive non-stop characters. Whatever we choose, the
heuristic needs to be very simple and fast to check, otherwise we just
introduce more overhead trying to decide which method to use.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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