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Home -> Community -> Mailing Lists -> Oracle-L -> confused about # of extents per segment performance issue
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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