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Home -> Community -> Usenet -> c.d.o.misc -> Re: the ways of buffer hit ratios are mysterious
attwoody wrote:
>
> Greetings, all
>
> I have some twelve (12) Oracle books, most of them dealing with tuning.
>
> In all of them, there are discussions about the Buffer Cache Hit Ratio,
> with the discussion being, "Thou shalt increase thy DB_BLOCK_BUFFERS in
> order to increase thy hit ratio"
>
> I've reorganized the database, increased DB_BLOCK_BUFFERS,
> rebuilt indexes, added indexes, etc, etc, etc. I've gone into the
> x$tables, I've set DB_BLOCK_LRU_EXTENDED_STATISTICS to see the
> effects of subtracting or adding buffers.
>
> It seems no matter how much I tweak and tune - some days, the hit
> ratio is in the 90's, some days it's in the 70's.
>
> Since the application is PeopleSoft 6, there's not a lot I can do
> to the code.
>
> It occurred to me that PeopleSoft has a lot of little tables that
> are used to retrieve data, and that a lot of table scans are being
> done - could this be contributing to what I'm seeing with the hit
> ratio? Would it be better to cache these small, frequently used
> tables?
>
> Another application I support called Glovia, has _excellent_
> performance statistics - but Glovia is _specifically_ written for
> Oracle - it has lots of stored procedures and packages, and takes
> advantage of Oracle performance enhancements. PeopleSoft's standard
> answer is "we want to make everything generic so it can run on
> any database". Well, it makes _my_ life more difficult!
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
Have a look at the multiple buffer pool feature...A lot of People soft implementations use the RBO and hence huge index scans and reads are common which can do nasties to the buffer cache (and hence the ratio)...
Possibly move your 'smaller' high use tables to the KEEP pool and the large index scans to the RECYCLE pool...
HTH
--
"Some days you're the pigeon, and some days you're the statue." Received on Sat Dec 18 1999 - 05:36:51 CST
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