Re: What MB/s is pulled from your buffer cache?

From: Martijn Bos <maboc_at_maboc.nl>
Date: Mon, 18 Feb 2013 21:44:15 +0100
Message-ID: <20130218204415.GA22054_at_app01.bos>



On Mon, Feb 18, 2013 at 07:48:33PM +0200, Tanel Poder wrote:
> This metric was added in 11.2.0.3.

It's probably in the release/upgrade notes from oracle so I could have known this. However...it would be nice if it was in the (online 11.2) documentation.

> I wouldn't use this metric for anything practical really as it doesn't
> represent the actual bytes transferred. It's just the number of times a
> buffer get was done times the block size.

You (well ... I) might wonder why this statistic is added in the first place. We can calculate it very easily from allready known statistics.  

>
> If you want to calculate it for some reason on earlier versions, then you
> can just multiply "session logical reads" with your DB block size. You're
> out of luck if you have multiple blocksizes.

Yeah...figured that out.  

> But again, it doesn't show the actual number of bytes
> transferred/processed. You don't have to scan through the entire 8kB block
> every time you do a buffer get. Also, if a buffer is kept pinned and
> re-visited thousands of times under that pin, the logical reads* stats do
> not go up even though you might be accessing data there a lot of times in a
> loop...

And now I learned something today (pinned block stuff). tnx.

Regards,
Martijn

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Received on Mon Feb 18 2013 - 21:44:15 CET

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