Another doubt about Hit ratio
DBAsupport.com Forums - Powered by vBulletin
Results 1 to 7 of 7

Thread: Another doubt about Hit ratio

  1. #1
    Join Date
    Jan 2001
    Posts
    642
    Hi,

    The general expression for the hit ratio is

    hit ratio = physical reads /(db block gets + consistent gets)
    (From v$sysstat).

    My question is, as the data grows,and the block size and other parameters being the same, the number of physical reads will be more
    ..
    So isn't that the hit raio should be more..

    please clarify...
    Badrinath

  2. #2
    Join Date
    Feb 2001
    Posts
    389
    Wrong
    Hit ratio is 1 - (your formula) * 100

  3. #3
    Join Date
    Jan 2001
    Posts
    642
    Sorry, talking about the buffer hit ratio.
    Badrinath

  4. #4
    Join Date
    Jan 2001
    Posts
    642
    Does rebuilding of indexes on all the tables improve the hit ratio.
    Badrinath

  5. #5

    Wink It'll improve the Disk I/O

    Rebuilding index will improve the Disk I/O usage but I don't think it'll help with hit ratio directly.
    Queyon Zeng

  6. #6
    Join Date
    Jan 2001
    Posts
    642
    So, is there any way other than increasing the buffer area to improve this hit ratio.

    Badrinath

  7. #7
    Join Date
    Feb 2001
    Posts
    389
    Ok , little confusion to clear here,

    Physical reads generally happen when the blocks are not found in the buffer and u have to do Disk I/O to load it into the buffer.

    If you think the db_block_buffers is high enough.

    You can do many things to improve hit ratio:

    1)Use multiple buffer pool startegy.
    2) For small lookup tables, cache them.
    3)Usage indexes properly (even though Oracle does not think the index blocks are in buffers and goes to disk but you can tune it with init.ora parameter which shall force Oracle to first look in buffers and then do disk i/o.
    Even then the number of disk i/o is less.
    4)Check disk sorting, use direct sorts , which is default in 8.1.6.

    But if buffers are less, u have no choice.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


Click Here to Expand Forum to Full Width