RE: Awr Units?
- From: "Kenneth Naim" <kennaim@xxxxxxxxx>
- To: "'Cary Millsap'" <cary.millsap@xxxxxxxxxxxx>
- Date: Fri, 22 May 2009 12:58:20 -0400
Thanks Cary,
I figured they were db blocks, not worrying so much if they were distinct or
not. I am using the awr data to show how much logical and physical io are
going on. How a 400gb database can churn through 20tb of data (logical io)
within 4 hours while only reading 200gb from disk. I just wanted to verify
that my calculation of multiplying the block size by the number of logical
io's per second by 4 hours before publishing the number. I am proving a
point to an applications group that hardware will not solve their
performance issues but sql tuning will.
This brought up the whole issue of AWR's not having units listed on many of
its metrics and I was hoping Oracle (or someone) published a document
showing the units and maybe an explanation of each metric.
Ken
From: Cary Millsap [mailto:cary.millsap@xxxxxxxxxxxx]
Sent: Friday, May 22, 2009 10:53 AM
To: kennaim@xxxxxxxxx
Cc: ORACLE-L
Subject: Re: Awr Units?
Ken,
The pio stats that Oracle emits in its V$ views and Oracle trace files are
in units of "number of Oracle blocks obtained by OS read calls." I don't
mean read literally: they might be read(), or pread(), or readv(), etc. The
lio stats (e.g., exposed in the trace data as cr and cu) are expressed in
units of "number of database buffer accesses." Note that this does not mean
the same thing as "number of database blocks." For example, cr=10000 may
mean that 10,000 different blocks were accessed, but it may well mean that
the same db block was accessed in the database buffer cache 10,000 times.
You can't know from the single 10000 statistic anything about the number of
distinct blocks accessed.
Cary Millsap
Method R Corporation
http://method-r.com
http://carymillsap.blogspot.com
http://twitter.com/cary_millsap
On Fri, May 22, 2009 at 9:27 AM, Kenneth Naim <kennaim@xxxxxxxxx> wrote:
Many of the Statistics on a 10gR2 AWR do have units listed and while most
are self explanatory or can be assumed quite easily, I was wondering if
anyone could point me to a document that spelled out each statistic and it's
appropriate unit. Logical Reads, Physcial Reads/Writes are examples of stats
without units and while I assume them to all be db blocks, a single physical
read could be multiple db/os blocks depending on how it is defined.
A metalink and google search has not yielded any results as of yet.
My college professors al.ways said "A number is meaningless unless it has
units".
Thanks,
Ken
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