From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Naz Gassiep <naz(at)mira(dot)net> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Hash Indexes |
Date: | 2008-01-07 20:10:11 |
Message-ID: | 24582.1199736611@sss.pgh.pa.us |
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Lists: | pgsql-general |
Naz Gassiep <naz(at)mira(dot)net> writes:
>> Why are hash indexes "obviously" best? In an ideal world with a good
>> implementation maybe, but postgresql b-trees are really quite good.
>>
> Because doing normal queries on a table where there are large text
> blocks is unlikely to be a good idea. E.g.,:
> SELECT * FROM table WHERE textcol = 'a 4kb block of text';
You seem to be harboring some rather severe conceptual errors about
how hash indexes work, or at least how Postgres' hash indexes work.
I get the impression you think that a hash index stores only a hash
code and not the actual field value, but that's not so.
regards, tom lane
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