From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
---|---|
To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
Cc: | Teodor Sigaev <teodor(at)sigaev(dot)ru>, Patches <pgsql-patches(at)postgresql(dot)org> |
Subject: | Re: Partial match in GIN |
Date: | 2008-04-08 19:29:45 |
Message-ID: | 47FBC7A9.4070803@enterprisedb.com |
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Lists: | pgsql-patches |
Alvaro Herrera wrote:
> Heikki Linnakangas wrote:
>> Teodor Sigaev wrote:
>
>>> GIN speeds up '%foo%' too - which is impossible for btree. But I don't
>>> like a hack around LIKE support in BTree. This support uses outflank
>>> ways missing regular one.
>> You could satisfy '%foo%' using a regular and a reverse B-tree index,
>> and a bitmap AND. Which is interestingly similar to the way you proposed
>> to use a TIDBitmap within GIN.
>
> Huh, can you? I can see doing "col LIKE 'foo%' OR reverse(col) LIKE
> reverse('%foo')" with two btree indexes, but not a true %foo% ...
That should be AND, not OR..
Hmm. It is the same as far as I can see. Am I missing something?
You couldn't support more complex patterns directly, like 'foo%bar%foo',
but you could still split that into 'foo%' AND '%bar%' AND '%foo', and
recheck the matches against the original pattern
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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