From: Mohamed El-Mallah <mie@mainruis.sannet.gov>
Subject: Re: Does the number of extents affect the performance?
Date: 1997/09/09
Message-ID: <34162F51.F1972249@mainruis.sannet.gov>#1/1
References: <5un2d4$ij4$1@news.minn.net> <34125df1.8307375@newshost>
X-Priority: 3 (Normal)
Newsgroups: comp.databases.oracle.server



The number of extents in table does not affect the performance of full
table scans as long as
the size of the extents is a multiple of the sizeof each read performed
(DB_FILE_MULTIBLOCK_READ_COUNT * DB_BLOCK_SIZE)
Mohamed El-Mallah
SDDPC

Thomas Kyte wrote:

> >After reading several articles, I get an imprsssion that the  fewer
> >extents in a table's data segment, the better the performance would
> >be. But I can't find this statement in any official document.
> >So I want to ask the experienced DBA about the relation between the
> >size of extent and the performance.
> >
>
> No, performance for a 1 extent table will be no different then a 100
> extent
> table.  this (few extents = better performance) is a rumor.
>
> On many databases, you can run export with compress=y and see a
> measurable
> performance improvement in the resulting imported database.  The
> serious flaw
> with using this data point as a "proof" that few extents is good
> is that you can use compress=n and achieve identical performance
> gains.  The
> performance gains come not from reduction in the number of extents in
> database
> segments, but from the block packing and row fragmentation removal
> implicitly in
> any import.