Re: Why "Separating Data and Indexes improves performance" is a myth?
- From: Kip.Bryant@xxxxxxxxxx
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 23 Apr 2004 10:33:05 -0700
Not to expand on the myth (and not exactly focus on Oracle) but didn't there
used to be a lot of effort made to reduce seek time (the little read/write head
zinging back and forth unnecessarily) by distributing files (right or wrong)?
Striping/mirroring/SAN technology also blasted this myth, right?
Kip Bryant
|> If they are both accesed at the same time, it will improve performance
|or
|> not,
|> I don't understand exactly what is this myth about?
|From the perspective of a single query, the indexes are not accessed at
|the same time
|as the data. Take a look at a trace file to verify it if you like.
|From the perspective of many queries executing simultaneously, it still
|doesn't really
|matter. You have several queries access both data and indexes. There can
|be
|contention for either one.
|What matters is the performance of your system under load. If you have 10
|disks in
|a RAID 0 with all indexes and data residing on it and the performance is
|somewhat
|lackluster, splitting those disks into two 5 disk RAID 0 drives and
|physically separating
|the indexes and data will not improve performance.
|It would be very likely though that it would decrease performance,
|particularly on
|full table scans and fast full index scans.
|Jared
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