Re: Awr Units?

From: Cary Millsap <cary.millsap_at_method-r.com>
Date: Fri, 22 May 2009 09:52:31 -0500
Message-ID: <3a2a84fc0905220752g582b9883x6afabebe1110601f_at_mail.gmail.com>



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

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On Fri, May 22, 2009 at 9:27 AM, Kenneth Naim <kennaim_at_gmail.com> 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 itís
> 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 ďA number is meaningless unless it has
> unitsĒ.
>
>
>
> Thanks,
>
> Ken
>

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Received on Fri May 22 2009 - 09:52:31 CDT

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