Re: "direct path read" and "db file sequential read" used for full table scans in 11g

  • From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
  • To: "Oracle-L List" <oracle-l@xxxxxxxxxxxxx>
  • Date: Fri, 31 Aug 2012 17:24:40 +0100

Gaja,

I misread your original posting - I thought you were saying that this would 
happen with direct path reads as well.

It's not difficult to engineer a case where every other block of a table 
has been loaded into the cache, at which point a (cached) full tablescan 
would read the other alternating half using single block reads - but if 11g 
chose to do direct path reads it would still do reads that were generally 
the 1MB.


Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com/all_postings

Author: Oracle Core (Apress 2011)
http://www.apress.com/9781430239543

----- Original Message ----- 
From: "Gaja Krishna Vaidyanatha" <gajav@xxxxxxxxx>
To: "Oracle-L List" <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, August 31, 2012 5:13 PM
Subject: Re: "direct path read" and "db file sequential read" used for full 
table scans in 11g


| Hi Jonathan, Mark et al.,
| My writeup was for a "simple full table scan" (like the example I gave), 
just to point out that "db file sequential reads" does occur for full 
scans. And yes, I am sure about that. This is true even with nothing else 
happening on the database (like delayed block cleanout). I was just 
wondering whether a similar phenomenon was being experienced with ADR.
|
| Cheers,
|
| Gaja
|
| Gaja Krishna Vaidyanatha,
| CEO & Founder, DBPerfMan LLC
| http://www.dbperfman.com
| http://www.dbcloudman.com
|
| Phone - +1-650-743-6060
| LinkedIn - http://www.linkedin.com/in/gajakrishnavaidyanatha
|
| Co-author: Oracle Insights:Tales of the Oak Table - 
http://www.apress.com/9781590593875
| Primary Author: Oracle Performance Tuning 101 - 
http://www.amzn.com/0072131454
| Enabling Cloud Deployment & Management for Oracle & Big Data

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