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Home -> Community -> Mailing Lists -> Oracle-L -> Re: v$sqlarea statistics
Hi Deepak,
Can you elaborate what is consistent gets
here's a high level from my understanding on this issue:
Buffer gets {also called Logical IO's}
These happen as oracle scans blocks of data in the
buffercache(in-mem scans). Many people believe that
since these are memory reads, they are inexpensive. I
have seen the contrary in many cases and have seen
that these are the ones which take the most cpu
clycles, therby making your system CPU Bound.
Resolution of this is to tune your sql by having it
use better access paths (indexes). Also consider
de-norming in ordr to avoid too many joins
I consider this the most important metrics in
identifying "bad" SQL. i have seen cases where
frequently executed queries were performing millions
of LIO's and hosing up the CPU. A simple index / or
Adding hint can reduce this number by a very high
factor resulting in great gains.
DiskReads {also called physical IO's)
This obviously means that there are a lot of disk
reads required to satisfy your query. Reasons: maybe
you are using ineffcient access paths/bad sql or u
just have insuffient (small) memory to support your
app. High Diskreads is the reason that makes your
system IO bound. Resolution is again the same as
described above. In addition, one of the assumtions
here is that you have spread your datafiles/logs/cf
optimally. Also consider using the recycle buffer pool
feature to avoid an innocent FTS from flushing
everything from your cache. Obviously you cannot
always prevent any of these and some disk read are
inevitable.
hth
Deepak:
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