Re: FTS waiting on db file sequential reads?
- From: Chris Taylor <christopherdtaylor1994@xxxxxxxxx>
- To: Riyaj Shamsudeen <riyaj.shamsudeen@xxxxxxxxx>
- Date: Thu, 18 Sep 2014 16:24:05 -0500
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@xxxxxxxxx> 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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