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Rainer Herbst wrote:
> Peter schrieb:
>> Is it a must to place datafiles, undo segments and table index on >> separate disks? If not, what are the benefits of doing so? >> >> Thanks >> >>
Why will this myth not simply die quietly as it should? There's no performance benefit to separating indexes from tables, and the disk head movement argument is just spurious. On a multi-user system, your disk head will probably move in between reads of rows from even a single table, because of the I/O requests that other users are making. Even on a single user system, your disk head moves between *tables* when you read two or more of them in a single SQL statement (ie, a join): so you get disk head movement, with not an index in sight.
Never mind that the blocks of an extent of a single segment are not contiguous on disk (unless you use raw partitions), so that even doing a full table scan your disk head is bobbing all over the place.
So yes, you can separate indexes from tables to eliminate the head movement, only to discover that the head movement happens because of other reasons. You might as well store every single segment in its own unique data file if that's going to be your argument. And don't forget to dump your file system whilst you're at it, because for true sequential access to Oracle blocks involving minimal head movement you're going to need raw.
Sorry Rainer. This one's been done to death, and the argument won't fly.
Regards
HJR
Received on Tue Sep 30 2003 - 03:05:27 CDT