Re: Cache Hit Ratio from system views


"DA Morgan" <damorgan@xxxxxxxxx> wrote in message
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Bob Jones wrote:
"Niall Litchfield" <niall.litchfield@xxxxxxxxx> wrote in message
news:1188811168.606148.130030@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On 1 Sep, 01:29, "Bob Jones" <em...@xxxxxx> wrote:
If the BCHR is an objective indicator, please tell us of what you
think
it is an indicator, and how - specifically you would use it. Richard's
indicator (as mine) is how long business transaction take. Definitely
objective and relatively straightforward to use and understand.
BHCR shows disk i/o percentage. An important indicator for buffer cache
tuning.
So how exactly would you use it? If BCHR falls below a certain value
increase one or more of the pool sizes? If it rises above a certain
value reduce them?

As I said before, response time is not even a database metric.
well no it isn't, it's a metric for the measurement of the performance
of the application as experienced by the end-user. Round in my part of
the world we install and use applications to support line of business
transactions and it is those installations that we care about rather
than the individual component. That's the primary reason that a metric
derived from business usage makes most sense to me.

It is an effect not a cause.
That's true enough, but breaking down the response time into it's
component parts, say
Time spent at web server
Time spent in application server
Time spent on network
Time spent in DB.

At a gross level gives you a much better tuning methodology than
requests satisifed from cache for any given component of the stack.
Producing an execution profile for the objects of interest really
shouldn't be news given that it was first described and demonstrated
by Knuth when I was 4 (and I'm ten times that age this year). The more
each of those tiers allow you to break down the response time
components the better you chance of finding the problems.

With some people's logic here, even response time is
meaningless. 5 minutes response time can be better than 5 seconds
response
time, if it is doing 5000 times more work.
That would likely depend on your requirements, in Richard's ATM
analogy it would seem unlikely that many banks would prioritise
keeping all their customers waiting 5 minutes to withdraw cash over
allowing a smaller subset to be happy with their 5 second response. On
the other hand if the per customer end of month statement takes 5
seconds, but the batch process for 5000 takes 5 minutes then I know
which I'd be scheduling in my month end process.


You are missing the point of this long thread. To avoid further branching
out to different topics, I would recommend reading it.

No Bob. The only one missing the point, repeatedly, is you.

You have been incorrect, you are incorrect, and given your propensity
to try to win arguments by virtue of tenacity rather than facts, it
appears that you always will be incorrect.


Someone who has only posted a couple of useless comments in this thread is
actually producing facts? Now that's news.

To quote the Oracle docs:
"A low cache hit ratio does not imply that increasing the size of the
cache would be beneficial for performance. A good cache hit ratio could
wrongly indicate that the cache is adequately sized for the workload."


Finally, something useful, but quoted from the doc. Notice the words like
"could" or "would"?
The second sentence is a little vague. What does "good" mean? Is my cache
still too small, if BCHR is 99%?

BHCR is as worthless as your unwillingness to acknowledge you are wrong.


I take it our buddy Dan here doesn't tune his buffer cache.

But given that your name is valid, and your email is not valid, why
would anyone expect your opinion to be valid? Come on out of the closet.

It appears valid names are more important to you than valid arguments.
Unlike you, I am not here to promote myself or anybody else.


.

Relevant Pages

  • Re: Cache Hit Ratio from system views
    ... indicator is how long business transaction take. ... but breaking down the response time into it's ... Time spent in application server ... "A low cache hit ratio does not imply that increasing the size of the cache would be beneficial for performance. ...
    (comp.databases.oracle.server)
  • Re: Cache Hit Ratio from system views
    ... it is an indicator, and how - specifically you would use it. ... indicator is how long business transaction take. ... but breaking down the response time into it's ... Time spent in application server ...
    (comp.databases.oracle.server)
  • Re: Cache Hit Ratio from system views
    ... it is an indicator, and how - specifically you would use it. ... indicator is how long business transaction take. ... but breaking down the response time into it's ... Time spent in application server ...
    (comp.databases.oracle.server)
  • Re: Cache Hit Ratio from system views
    ... it is an indicator, and how - specifically you would use it. ... indicator is how long business transaction take. ... but breaking down the response time into it's ... Time spent in application server ...
    (comp.databases.oracle.server)
  • Re: Cache Hit Ratio from system views
    ... it is an indicator, and how - specifically you would use it. ... indicator is how long business transaction take. ... but breaking down the response time into it's ... Time spent in application server ...
    (comp.databases.oracle.server)