Re: BCHR Tuning

From: Robert Eskridge <bryny_at_dfweahs.net>
Date: Fri, 10 Jan 2003 08:04:50 -0800
Message-ID: <F001.0052C5DA.20030110080450@fatcity.com>

Of course it dropped dramatically. That's because you are no longer doing 99% of the buffer gets that you were wasting to begin with.

If it drops my resource use and increases my performanc, I'd love to have a BCHR of 1%. (I know that's extreme, but wouldn't it be cool..?)

F> Here's an excellent real life example of why BCHR is not a good tuning
F> metric and you should focus on reducing I/Os.
F> A simple fix for a query and here is the resulting email to the client, who
F> understands that BCHR is not good. A little techie humor...
 

F> I have good news and I have bad news.

F> The good news is that the elapsed query time and total I/Os for the latest F> iteration dropped significantly.

Old -->> 1:42 min 2,715,659 i/os (15,925 physical)

New -->> 22 seconds 3318 i/os (2861)

F> However, the bad news is that the Buffer Cache Hit Ratio dropped F> dramatically!

Old -->> 99.36%

New -->> 13.77%

F> So, I have undone all the changes I made and will begin looking at other F> methods to improve performance!

-rje

--

Please see the official ORACLE-L FAQ: http://www.orafaq.net
--

Author: Robert Eskridge
  INET: bryny_at_dfweahs.net

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services


---------------------------------------------------------------------

To REMOVE yourself from this mailing list, send an E-Mail message

to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). Received on Fri Jan 10 2003 - 10:04:50 CST