From: Tom Lane <tgl@sss.pgh.pa.us>
To: Guillaume Smet <guillaume.smet@gmail.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: Index creation time and distribution
Date: Thu, 22 May 2008 09:14:36 -0400
Message-ID: <29529.1211462076@sss.pgh.pa.us> (raw)
In-Reply-To: <1d4e0c10805220532v514c2bd5je4c6c20ceb485495@mail.gmail.com>
References: <1d4e0c10805220532v514c2bd5je4c6c20ceb485495@mail.gmail.com>
"Guillaume Smet" <guillaume.smet@gmail.com> writes:
> I experienced this morning a performance problem when we imported a
> dump in a 8.1 database.
> The table is 5 millions rows large and when the dump creates an index
> on a specific text column called clazz it takes 27 minutes while on
> the other columns, it only takes a couple of seconds:
> The only weird thing about this column is that 4.7 millions of rows
> have the exact same value.
Do you have maintenance_work_mem set large enough that the index
creation sort is done in-memory? 8.1 depends on the platform's qsort
and a lot of them are kinda pessimal for input like this.
8.2 (which uses our own qsort) seems to perform better in a quick
test.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, guillaume.smet@gmail.com
Subject: Re: Index creation time and distribution
In-Reply-To: <29529.1211462076@sss.pgh.pa.us>
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