From: | Vadim Mikheev <vadim(at)krs(dot)ru> |
---|---|
To: | scott jacobs <sjacobs(at)imagicgames(dot)com> |
Cc: | pgsql-general(at)hub(dot)org |
Subject: | Re: [GENERAL] Hash index performance/operation questions... |
Date: | 1998-07-15 02:38:01 |
Message-ID: | 35AC1609.AB2B3428@krs.ru |
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Lists: | pgsql-general |
scott jacobs wrote:
>
> Hi! I'm a bit confused regarding hashed indexes in postgres. I'm hoping
> someone can either answer my questions or point me towards some
> documentation that answers them.
>
> How come the performance of a hashed index created on an empty table into
> which data is copied is so poor (on my machine)? Selects from this table
> are really no faster than on an unindexed table. Once the table is loaded,
> if I drop and recreate the index, performance is much better (at least 9X
> in my case). Am I misunderstanding the part of the create_index man page
> that says:
> "We mention the algorithms used solely to indicate that all
> of these access methods are fully dynamic and do not have to
> be optimized periodically (as is the case with, for example,
> static hash access methods). "
>
> Is there a chance that copying the data into the table has something to do
> with it? Does the index still get dynamically optimised if I'm not
> inserting the data? I am going to try inserting the data later, but don't
> have access to the database right now and I thought maybe I can get an
> answer before then.
Indices are dynamic, but statistic about table pages/rows is not:
run vacuum or, better, create index AFTER loading data into table -
this is faster.
Also note, that nothing was done for hash indices last 2 years -
btree are the most supported indices...
Vadim
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