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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Big SGA.......
Please start using STATSPACK now to gather and keep statistics. You are certainly going to need "before" and "after" statistics to analyze.
Some questions:
a.. Why does the development group think that I/O is the problem? Have they been gathering data? Have you seen it? Do you concur that their data proves that I/O is a performance problem belonging to the Oracle database?
b.. Let's assume that there is an I/O problem. There are two ways to address I/O (as stated in the YAPP report of www.oraperf.com): reduce the *cost* per I/O request or reduce the *number* of I/O requests. The former implies getting a better/faster I/O subsystem, redistributing I/O load to different volumes, etc. Not trivial. The latter implies improving the Buffer Cache Hit Ratio (BCHR) by increasing the size of the Buffer Cache or it implies making queries more efficient, so that they simply don't issue so many I/O requests (either to the Buffer Cache or to the disk).
Gathering STATSPACK data and searching for the SQL statements generating the largest number of "physical I/O" requests might be illuminating for the developers. If you work with them on a one-by-one basis on tuning each of these SQL statements, you might see dramatic improvements in performance.
Suggest to them that *after* you are confident that there are no tunable SQL statements, then you might consider increasing the size of the Buffer Cache. Doing so is a last resort, not a first response. This is because doing so does not fix the real problem, it only accomodates the real problem, which is inefficient SQL.
Hope this helps...
-Tim
hey folks.. Hoping for a little feedback and opinion please. Having a discussion with the development group ...
The development group is thinking that a VERY LARGE SGA would solve some of their I/O problems. For example, they believe that a SGA consisting of over 8GB of db block buffers would resolve their multitude of issues. I feel that they open another can of worms with something such as this.. And granted-there hasn't really been an infrastructure evaluation-and the SA group is currently performing that review of the environment.
One could suggest that they could "cache" some very large tables in the SGA; but there seems to be some sense of a down side to this.. Could you all provide some input on "Extremely large SGA's"? In the area of 8GB or so.. BUT, most of this would be the database blocks. Would you all be so kinds to provide your thoughts please?
TIA
Greg Loughmiller
Sr Manager - Enterprise Data Architecture
gloughmiller (IPS)
678.893.3217 (office)
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Author: Tim Gorman
INET: Tim_at_SageLogix.com
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