Blocked vs. non-blocked pages

Posted on 2004-11-23
Last Modified: 2009-12-16
What is the difference between blocked and non-blocked pages in a bufferpool and how do they affect performance?

Thank you in advance.
Question by:aporras
    LVL 13

    Expert Comment

    Block based bufferpools allow performance improvement for sequentail prefetching. From the db2 docs:
    A block-based buffer pool consists of both a page area and a block area. The page area is required for non-sequential prefetching workloads. The block area consists of blocks where each block contains a specified number of contiguous pages, which is referred to as the block size (normally pages are read into the bufferpool by reading contiguous pages on disk into non contiguous pages in memory).
    When a block based buffer pool is available, the prefetching code recognizes this and will use block I/Os to read multiple pages into the buffer pool in a single I/O significantly improving the performance of prefetching. The BLOCKSIZE parameter of the CREATE and ALTER BUFFERPOOL SQL statement defines the size of the blocks, and hense the number of pages read from disk in a block I/O.


    Author Comment

    I'm still not sure what the difference is between blocked and non-blocked pages... and if I am understanding your comment there would never be any value in non-blocked pages yet when looking at the GUI in DB2 UDB 8.2, it defaults to all pages in a bufferpool being non-blocked.
    LVL 13

    Accepted Solution

    yes that is the default setup , you have to explicitly create the block based bufferpools with alter bufferpool or with create bufferpool .....NUMBLOCKPAGES  ... BLOCKSIZE     keywords

    the difference is the way in which the data pages are read into the bufferpool

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