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From "Karl Baum" <kb...@tallan.com>
Subject Fw: TCP Lateral Caching bug fix
Date Mon, 16 Jun 2003 13:16:42 GMT
Sorry for the repeat email.  I am having technical difficulties.  This
attachment should be correct.


----- Original Message ----- 
From: "Baum, Karl" <Karl.Baum@Tallan.com>
To: "Turbine JCS Developers List" <turbine-jcs-dev@jakarta.apache.org>
Sent: Sunday, June 15, 2003 10:22 PM
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/la
> teral/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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