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Re: Large initial extent after import

From: Neil Hulin <nospam_at_litech.freeserve.co.uk>
Date: Fri, 13 Nov 1998 10:25:49 -0000
Message-ID: <72h1h9$3bi$1@newsreader1.core.theplanet.net>

Jan Dolman wrote in message <364b52d3.360440_at_news.a2000.nl>...
>When importing an export file that was exported using COMPRESS=Y,
>Oracle creates an inital extent for each table large enough to hold
>the entire table. For some tables, this initial extent can be quite
>big.
>Questions:
>Is there a good reason to want this large extent?

Yes, do not underestimate the performance hit if you have a table or index with many (say, more than 10) extents.
Read the Oracle documentation and get a copy of Corrigan and Gurry.

I have experience of 13GB tables and decided on 13 x 1GB extents to reduce waste space to an average of 500Mb per table. Previously these tables were up to 11,000 extents and operations would take in excess of 8 hours on a Sun ES10000 with 38 processors, 26GB RAM and 1.5TB mirrored EMC frames. After the reorg to reduce the number of extents we had most operations down to four minutes.

>Is there a good reason NOT to want this large extent?

Yes, when the extent size is greater than the maximum file size for the system you are hosted on. This is typically 2GB for most breeds of UNIX, so a 30GB table won't fit in a single extent.

...neil {actually: neil [dot] hulin [at] litech [dot] freeserve [dot] co [dot] uk} Received on Fri Nov 13 1998 - 04:25:49 CST

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