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Re: Oracle-managed RAID-like tablespaces

From: roobaron <member_at_dbforums.com>
Date: 29 Jul 2002 12:23:02 GMT
Message-ID: <3d4533a6$1@news.usenetgateway.com>


Had a quick look at the doco (concepts manual) for 8.1.7 doesn't mention that data is written in a round robin fashion, the algorithm will write to the same datafile as long as there is contiguous space, only looking at the other datafile if there is not enough space.

Here it is from the horse's mouth

"Allocating Extents in Locally-Managed Tablespaces In locally-managed tablespaces, Oracle looks for free space to allocate to a new extent by first determining a candidate datafile in the tablespace and then searching the datafile's bitmap for the required number of adjacent free blocks. If that datafile does not have enough adjacent free space, Oracle looks in another datafile."

What you are trying to achieve is striping for reads... we are talking somewhere in the vicinity of 8k reads per I/O depending on the disk I/O setup. To stripe the data exactly so that your app gets the multiple disk heads retrieving via Oracle is not worth the effort.

Use OS striping or a decent LVM as mentioned.

Hope this helps save time

--
An Oracle DBAs undocumented init.ora parameters

_OVERCOME_POOR_DESIGN = TRUE
_DISABLE_BAD_PERFORMANCE = TRUE
Posted via dBforums http://dbforums.com
Received on Mon Jul 29 2002 - 07:23:02 CDT

Original text of this message

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