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From "Baum, Karl" <Karl.B...@Tallan.com>
Subject FW: TCP Lateral Caching bug fix
Date Mon, 16 Jun 2003 13:07:26 GMT
I believe the last attachment was not correct.  Let me try again.

 

-----Original Message-----
From: Baum, Karl 
Sent: Sunday, June 15, 2003 10:23 PM
To: Turbine JCS Developers List
Subject: TCP Lateral Caching bug fix

 

I noticed a problem with lateral caching when configuring two or more TCP
servers.  The problem has to do with lateral cache recovery process when
losing connections.  I have attached a fix. 

 

 

Main Issue:

 

I have three lateral cache servers.  I start one server first.  Because the
other lateral TCP servers are not yet running, the first server fails to
connect to the others and begins recovery mode.  In recovery mode, a
LateralCacheMonitor thread runs every 20 seconds trying to create
connections to the other servers.  I noticed the thread was only trying to
create a connection to one of the other cache servers.  The result was that
when I brought the other two servers up, the initial server only
successfully connected to one out of the other two servers.  This was always
the last of the TCP servers in the comma separated list.

 

Cause:

 

The problem is caused by the reuse of the same LateralCacheAttributes
object.  For each of the TCP servers, a LateralCacheManager is created.
Each LateralCacheManager is created with an instance of
LateraCacheAttributes.  Before instantiating the LateralCacheManager, the
specific TCP server is set on the LateralCacheAttributes object.  Since the
same instance of LateralCacheAttributes is used each time, the call to set
the TCP server overwrites the previous TCP server each time.  In recovery
mode, the TCP server property on the LateralCacheAttributes is used to
reestablish the connections.  Recovery mode will always attempt to
reestablish a connection to the last of the TCP servers since this was the
last server to be set in the LateralCacheAttributes object.

 

Fix:

 

To fix this issue, I modified the class LateralCacheFactory.  Now
LateralCacheFactory calls set TCP server on a clone of the
LateralCacheAttributes object.  As a result, the previous TCP server is not
overwritten.

 

CVS diff: 

 

$ cvs -d :pserver:anoncvs@cvs.apache.org:/home/cvspublic diff -u
LateralCacheFactory.java

Index: LateralCacheFactory.java

===================================================================

RCS file:
/home/cvspublic/jakarta-turbine-jcs/src/java/org/apache/jcs/auxiliary/latera
l/LateralCacheFactory.java,v

retrieving revision 1.4

diff -u -r1.4 LateralCacheFactory.java

--- LateralCacheFactory.java    7 Aug 2002 15:28:12 -0000       1.4

+++ LateralCacheFactory.java    16 Jun 2003 02:14:43 -0000

@@ -73,15 +73,16 @@

             StringTokenizer it = new StringTokenizer( lac.tcpServers, ","
);

             while ( it.hasMoreElements() )

             {

+               LateralCacheAttributes lacClone =
(LateralCacheAttributes)lac.copy();

                 //String server = (String)it.next();

                 String server = ( String ) it.nextElement();

                 if ( log.isDebugEnabled() )

                 {

                   log.debug( "tcp server = " +  server );

                 }

-                lac.setTcpServer( server );

-                LateralCacheManager lcm = LateralCacheManager.getInstance(
lac );

-                ICache ic = lcm.getCache( lac.getCacheName() );

+                lacClone.setTcpServer( server );

+                LateralCacheManager lcm = LateralCacheManager.getInstance(
lacClone );

+                ICache ic = lcm.getCache( lacClone.getCacheName() );

                 if ( ic != null )

                 {

                     noWaits.add( ic );


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