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<== Date ==> <== Thread ==>

Subject: Re: Memory usage by CA server
From: hill@luke.atdiv.lanl.gov (Jeff Hill)
To: bickley@cebaf.gov
Cc: tech-talk@aps.anl.gov
Date: Tue, 17 Oct 95 10:44:10 MDT
Matt,

>    What is the expected behaviour of the CA server when available free memory
> (or the largest free block) gets low on an IOC?  We have occasionally had
> situations where free memory gets to ~200 KB and the largest free block gets
> to ~50-80 KB.  The next time a client attempts a connection we see the warning
> "Unable to allocate additional dynamic memory".  I believe that the CA server
> is working as it should.  Is this true?

The CA server attempts to prevent additional memory consumption 
after the max free block value drops below 100k. It is difficult 
under vxWorks to examine the max free block value efficiently
because the routine provided examines every free block. They (WRS)
should probably keep track of the max free block on the fly.
Because of these inefficiencies we poll the max free block value 
every few seconds. This opens up the possibility of a fast client
using up the memory pad before the next time that the max free block
value is polled.

Under EPICS 3.12.1. when the max free block
drops below 100k the server will not allow any additional channels to 
be created even if the server's free list is populated. This can result
in failure to communicate with an overloaded IOC even if some of 
the clients attached to the IOC are stopped in an attempted to 
reduce the load. I have made changes for 3.12.2 to allow new channels 
if the max free block is above 100k _or_ if the appropriate free
lists are populated.

Jeff

______________________________________________________________________
Jeffrey O. Hill			Internet	johill@lanl.gov
LANL MS H820			Voice		505 665 1831
Los Alamos, NM 87545 USA 	FAX		505 665 5107



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