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confused about # of extents per segment performance issue

From: dana mn <danamn2000_at_yahoo.com>
Date: Tue, 27 Feb 2001 10:43:11 -0800
Message-ID: <F001.002BE930.20010227100622@fatcity.com>

Apparently, it's a widely held myth that a large # of extents (let's say "BETWEEN 5 AND 1000") per table segment is bad for performance. Yet the same sources who label the belief mistaken persist in pushing for fitting all of a table in the INITIAL extent.

And that confuses the heck out of me.

What gives?

Is it that fetching a new extent on the fly, the act of obtaining a new extent, creates too much overhead? And finis, no more concern beyond this?

If you approached a database for the first time and it already contained a segment with 500 extents, would that segment's number of extents not be a performance concern unless you expected it to continue grabbing new extents? Let's say it would never have a new insert, update, or delete. Would there be any performance value in crushing the segment down to fit in one extent?

What's the definitive answer on this?

I remain confused about coalescing as well; anyone know of a good whitepaper or article on coalescing/fragmentation for Oracle 8 and beyond?

Thanks.


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Author: dana mn
  INET: danamn2000_at_yahoo.com
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