Re: Create Index (Hash) on a Large Table Taking Days...

From: "Harald Armin Massa" <haraldarminmassa(at)gmail(dot)com>
To: pgsql-general(at)postgresql(dot)org
Subject: Re: Create Index (Hash) on a Large Table Taking Days...
Date: 2008-01-08 14:56:11
Message-ID: 7be3f35d0801080656h61b06f4ft6837f5099e11e623@mail.gmail.com
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>I have a very large table (~5GB, 100mm rows) on which I am creating an
>index on an int4 column:

>CREATE INDEX CONCURRENTLY rums_idx2
> ON rums
> USING hash
> (user_id);

Why are you using a hash index on an int4 column?

as you have 100mm (mm= Million?) rows, only 1 GIG ram and the
column_name is "user_id", I suspect:
- you have far less then 100*10E6 Users
- there are less distince user_ids than rows

I just know "hash" from general programming, thatfor my belly is
announcing "hash collisions, hash collisions" ...

(within PostgreSQL I once read that hash indices are only for some
cases I could not match to something that happens in my world; since
then I am using default btree and am VERY happy.)

Best wishes,

Harald

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