Thursday Sep 25, 2014

Demantra Performance and Setup News

Hello!   Sorry for being away so long!  I have been preparing version 2 of the Demantra Performance and Setup Analyzer.  More on that soon.


Have you seen the latest 12.2.1, 12.2.2, 12.2.3 and 12.2.4 Install Upgrade ADVISOR: Demantra (Doc ID 1664177.2)?  This is an excellent store
of hand picked notes and white papers.  Including White Papers, How To +! Documents from Development.  Check it out and let me know what you think.
Regards!  Jeffv

Thursday Sep 06, 2012

AWR Performance Report and Read by Other Session Waits

For the questions regarding "read by other session" and its relation to "db file sequential/scattered read",
the logic is like this:


When a "db file sequential/scattered read" is done, the blocks are either already in the cache or on the disk.  Since any operation on blocks is done in the cache and since and the issue is "read by other session" I will relate to the case the blocks are on the disk.

Process A is reading the needed block from the disk to the cache.  During that time, if process B (and C and others) need the same block, it will wait on "read by other session".  A and B can be threads of the same process running in parallel or unrelated processes.  For example two processes doing full table scan on mdp_matrix etc.

Solutions for that can be lowering the number of processes competing on the same blocks, increasing PCTFREE.  If it is a full table scan, maybe an index is missing that can result in less blocks being read from the cache and so on.

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