Re: FTS waiting on db file sequential reads?

From: Chris Taylor <christopherdtaylor1994_at_gmail.com>
Date: Thu, 18 Sep 2014 16:24:05 -0500
Message-ID: <CAP79kiQbQBX8pFKAYjujCvJ5k6O_oybteofwqPeTd1ZZ+hgBmQ_at_mail.gmail.com>

Another team member killed the session so I don't have access to it now.

One of my coworkers was able to grab a trace of the session before it was killed and apparently it was reading UNDO segment information. Apparently reading UNDO is a db file sequential read. Makes sense but I hadn't ever really thought about it.

Regards
Chris

On Thu, Sep 18, 2014 at 3:07 PM, Riyaj Shamsudeen < riyaj.shamsudeen_at_gmail.com> wrote:

> Hello Chris
> Snapper should also spit out statistics for 'table fetch continued row'
> if you use gather=stw. Could you post the full output of snapper with
> gather=stw? That will give us more data.
>
> Second, AFAIK, full table scan should not follow the chain for migrated
> rows, except in the case of inmemory population:
> https://orainternals.wordpress.com/2014/09/11/inmemory-why-didnt-that-table-was-populated-in-the-column-store/
>
> Yes, dbms_stats doesn't populate chain_cnt. You must use analyze table..
>
> Another possibility is that may be the buffer cache already has blocks
> of the table cached and so, single block reads are performed.
>
> Cheers
>
> Riyaj Shamsudeen
> Principal DBA,
> Ora!nternals - http://www.orainternals.com - Specialists in Performance,
> RAC and EBS
> Blog: http://orainternals.wordpress.com/
> Oracle ACE Director and OakTable member <http://www.oaktable.com/>
>
> Co-author of the books: Expert Oracle Practices
> <http://tinyurl.com/book-expert-oracle-practices/>, Pro Oracle SQL,
> <http://tinyurl.com/ahpvms8> <http://tinyurl.com/ahpvms8>Expert RAC
> Practices 12c. <http://tinyurl.com/expert-rac-12c> Expert PL/SQL practices
> <http://tinyurl.com/book-expert-plsql-practices>
>
> <http://tinyurl.com/book-expert-plsql-practices>
>
>

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Received on Thu Sep 18 2014 - 23:24:05 CEST