Re: Database Buffer Cache Hit Ratio
- From: fitzjarrell@xxxxxxx
- Date: 6 Oct 2005 13:16:42 -0700
pcambraf wrote:
> I didnt like your off topic answers... if you dont want to help me just
> dont say nothing, i wasnt answering for been replyed like that...
>
> Im a DBA jr, in the applications side, cause the real DBAS wont fix
> anything, i just dont have access to sys or system or whatever could be
> called superuser, so i begin with handicap.
Yet you've stated in your original post the following:
| Hi people.
|
| I had an 8.1.7.4 database with a 68% of buffer hit ratio and 180 Mb
of
| cache, I've changed the db_block_buffers parameter so we have 234 Mb
of
| db buffer cache, and the hit ratio is now 57%, almost a 10% less!!.
| I'm mad about this, i've been looking around and i think it could be
a
| I/O retention in the only one DBWR process, ¿is this possible?
|
| Are there any other factors to consider?
|
| Thank you so much...
|
| Regards
Note this passage: "I've changed the db_block_buffers parameter ..."
How on earth did YOU perform such an act absent access to SYS? Yes,
you can change the value in the init.ora file yet you'll need SYS as
SYSDBA permissions (INTERNAL through SVRMGR) to stop and restart the
database so the changes will take effect. Did you do this without
express permission from the 'real DBAs'? Did you do this just prior to
a scheduled shotdown so your changes would take effect even though you
have no authority to make them? Unilateral decisions, made by someone
who is, at best, a JUNIOR member of the team, is not acceptable. Yet
you feel compelled to meddle in team affairs as a rogue member. As
it's been stated before if you don't have access to SYS you're not a
DBA, in any way, shape or form. Such actions may be why you're still
an almost junior member, and have no access to accounts with which you
could do real damage to the database. And, possibly, since the 'real'
DBA's 'won't fix anything' there is nothing to 'fix'?
> Anyway, im on a OLTP enviroment, with dictionary managment tablespaces,
> its a small system, about 3 o 4 gigs on disk and there are user
> complains, so much. The application is not well written, but fix this
> is not possible, they dont want to (another handicap), ive seen this db
> cache hit ratio so low, and i thought its a problem, and my question
> was: Could a contention in DBWR process (theres only one as ive said
> above) produce a low hit ratio in the instance?
Such an occurrence is not likely, as your poor code is the most likely
culprit in your 'low buffer cache hit ratio'. Of course it could also
be fueled by numerous one-off queries against any number of tables.
The BCHR numbers MAY be indicating a problem is existent, but they are
not the problem unto themselves. Ed Stevens gave you excellent advice:
generate a statspack report and upload it to oraperf.com. You'll
probably be surprised by the findings. And, possibly, your 'real DBAs'
have already done so, and discovered that in your situation there is
nothing to fix. They are the 'real DBAs' for a reason; I'd stop trying
to second-guess them at every turn.
David Fitzjarrell
.
- References:
- Database Buffer Cache Hit Ratio
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- Re: Database Buffer Cache Hit Ratio
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- Re: Database Buffer Cache Hit Ratio
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- Re: Database Buffer Cache Hit Ratio
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