Ganesh, I did not recall of mentioning Parallelism what I rote to Irfan, My answer was about multiple extents. Yes, I will stand on my ground that multiple extents (as I said extra ordinary) will affect the performance for full table scan, as the disk head had to reposition itself To make extra hits (I/O) for read and write/update, and extra block addresses in SGA for the records read. My understanding my logic, Ganesh most of the time I write from the top of my mind, After doing this work for so long, I do not go through the technical manual, My idea is not to write technical manual for every email or query, Email should give the major guide line on the issue and each one of us the user should go the extra 9 yards according to our needs. Believe me I ran Tara byte database and I don't have to prove, I had done my proving, Few extents are better that many. I am not an academic and I am running a shop and the time I have I enjoy answering emails and some time for fun add my logic. But Oracle is in the business of proving yes I can be wrong then you just have to say, Nisar here you are wrong. I will and you can give the understanding on an issue, its okay with me. Plus, extents are Physical blocks not logical. eg. 1 block of 10 giga bytes or 10 blocks of 1 biga bytes. Have Fun. Nisar Tareen Ganesh Raja <ganesh.raja@xxxxxxxxx> wrote: Nisar, Did not Understand too much from your Post .. But How does all the things that you have talked about affect the way parallelism works .. Parallelism is CPU Bound and not disk bound ... U dictate if you want to Use Parallelism and then The ur Query/DML is Split across multiple processess that works out how to fetch data from the database and processes it. I am disagreeing here with irfhan also when he says that Multiple extents will give u chances of better parallelism. U can write a small testcase with a One Extent Table and See what happens .. U will still get Parallel Reads. The Only thing that has some effect on performance with Multiple Extent is the MBRC value since an Multi Block read cannot be done over multiple extents. [ U will never encounter this has a Problem] Apart from that i will never say that if you have 1000 Extents ur Query is Going to Perform badly and if you have 1 Extent it will perform any better. I need a test case from u to prove that the otherway. Extent has always been a Logical Grouping of Blocks and not a Physicall Grouping. My $0.02 and not my logic ... :) Rgds Ganesh --------------------------------- Do you Yahoo!? Check out the new Yahoo! Front Page. www.yahoo.com