Thanx Jonathan, I did understand what you said, but still have a few questions regarding this. Are there any FMs or metalink notes from where I can get information on this subject so that I only come up with smart questions? Regards Naveen >-----Original Message----- >From: Jonathan Lewis [mailto:jonathan@xxxxxxxxxxxxxxxxxx] >Sent: Tuesday, February 17, 2004 3:36 PM >To: oracle-l@xxxxxxxxxxxxx >Subject: Re: How do commits release row level locks? > > > >I think Arup has been doing a lot of work with RAC >recently, and the article assumes that you may have >multiple free list group blocks. > >Moreover, if you have a default DBCA install of 9.2, >then your tablespace is probably ASSM (as mentioned >in Arup's last paragraph), and can't have multiple >freelist group blocks. > >The first potential data block will be immediately after >the segment header block; but there is a problem with >ASSM because the first batch of blocks at the start of >the first extent may not be the first block formatted. > >For ASSM the first extent blocks will usually be: > Level 1 bitmap > Level 2 bitmap > Segment header block > Available data blocks. > >For large extent sizes, the may be more than one Level 1 >bitmap block before the level 2 bitmap block. > >I tend to look at dba_segments for the location of the >segment header block (header_file, header_block), >then look at dba_extents, in order for the start of the >actual extents. (file_id, block_id). > >Historically, file_id, block_id of extent ZERO used to match >header_file, header_block of dba_segmentss; but with ASSM, >this is no longer true. > >To find out where your data blocks are on a SMALL test, >you need to dump the first block of the first extent to find >out which blocks in the extent are formatted. In general, >though, for a large, busy, table, all the space in everything >but the last extent has probably been formatted and used. > >My general approach to picking a few blocks are random >is to do > select file_id, block_id + 4 from dba_extents where ... >This usually picks one data block from each extent. > > >Regards > >Jonathan Lewis ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request@xxxxxxxxxxxxx put 'unsubscribe' in the subject line. -- Archives are at //www.freelists.org/archives/oracle-l/ FAQ is at //www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------