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fragmentation in LMT ? [message #184273] Wed, 26 July 2006 00:18 Go to next message
Messages: 142
Registered: March 2006
Senior Member
1) how is fragmentation controled in LMT ??

2) also are blocks used if they are free, but not in a continous representation.
ie. say block size 4k, but table update of 8k
free blocks due to deletes are 2 but they are not continous.


F=Free (due to deletes)

so will these 2 blocks be used ??
Re: fragmentation in LMT ? [message #184334 is a reply to message #184273] Wed, 26 July 2006 03:48 Go to previous messageGo to next message
Messages: 1016
Registered: March 2005
Location: Scotland
Senior Member
LMT & Fragmentation




When blocks a 'emptied' down to a certain level, they are made available for inserts. Updates are different. If you update a row, let's say that it is row 10 in block 1, and that update increases the size of the row, Oracle will simply perform the update, taking up more space in the current block.However, if the row grows large enough to require more space than is available in the block in which that row currently resides, Oracle will Migrate the row to another block where there is enough space, but leave a pointer in the original block to point to the row's new physical location. (This is bad as it would now require 2 I/Os to get that row)



the two blocks 'F' would be on the 'Free-list' of the segment, pointing out to Oracle that these blocks are available for inserts.

Read more from the documentation on
Extent Management, Segment Space Management, LMT's. There is a massive amount of info out there.

Re: fragmentation in LMT ? [message #184375 is a reply to message #184273] Wed, 26 July 2006 06:35 Go to previous message
Mahesh Rajendran
Messages: 10672
Registered: March 2002
Location: oracleDocoVille
Senior Member
Account Moderator
Just another worthy read

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