Re: db file sequential/scattered read

From: Brian Peasland <peasland_at_edcmail.cr.usgs.gov>
Date: Thu, 11 Jan 2001 17:27:10 GMT
Message-ID: <3A5DECEE.B42BDE81@edcmail.cr.usgs.gov>

> Regarding your words toward the end, I'm curious why Oracle reads db
> files into scattered memory locations instead of contiguous blocks.
> Does it always do so? Is it due to operating system memory
> fragmentation?

Oracle reads the data into the buffer cache. If there is no free space in the buffer cache, then Oracle must release data using the Least Recently Used (LRU) algorithm. This algorithm does not guarantee that data will be released in contiguous memory chunks. So the free memory locations of the buffer cache can become fragmented. Rather than reorganize the data in the buffer cache to obtain unfragmented free space, Oracle just reads the data into those fragmented holes of free space.

HTH,
Brian Received on Thu Jan 11 2001 - 11:27:10 CST