read by other session events

  • From: lyallbarbour@xxxxxxxxxxxxxxx
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Wed, 10 Nov 2010 17:19:26 -0500


 This morning we had our production database come to practically a 
grinding halt with lots of I/O requests in Grid.  running ADDM and ASH reports, 
there were, at first, problems with Segments that needed to be tuned.  Then the 
next ADDM reports talked about "read by other session" events being 100% the 
major problem.  
After looking through Oracle Support and more and more help desk calls coming 
in, we decided to bounce the database.  This, of course, solved our problem.

I don't really understand what "read by other session" events are, so if 
someone can clarify that, that would be helpful.  From what i read, they are 
memory waits for the data blocks in the buffer cache.  Different logins 
requesting the same blocks in memory... i think.  Even if that's right, i guess 
i still don't really understand what that means.

The other thing that i'd really like to know, if we ever encounter this again 
since we don't really know how it happened, what other options do i have 
instead of bouncing the database?  Flushing the buffer cache and SGA?  Killing 
peoples session that i see in ASH reports that have these "read by other 
session" wait events?

Thanks for any replies!

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