[infinispan-dev] Hashing generating recipient lists with same address

[Manik Surtani]

So TopologyChangeTest is a pretty complex test involving HotRod clients and servers, etc.  Can this be reproduced in a simpler setting - i.e., 2 p2p Infinispan instances, add a third, etc., without any HotRod components?

On 6 May 2010, at 17:51, galder at redhat.com wrote:

> Hi all,
> 
> As indicated on IRC, running org.infinispan.client.hotrod.TopologyChangeTest.testTwoMembers() fails randomly with replication timeout. It's very easy to replicate. When it fails, this is what happens:
> 
> 1. During rehashing, a new hash is installed:
> 2010-05-06 17:54:11,960 4932  TRACE [org.infinispan.distribution.DistributionManagerImpl] (Rehasher-eq-985:) Installing new consistent hash DefaultConsistentHash{addresses ={109=eq-35426, 10032=eq-985, 10033=eq-985}, hash space =10240}
> 
> 2. Rehash finishes and the previous hash is still installed:
> 2010-05-06 17:54:11,978 4950  INFO  [org.infinispan.distribution.JoinTask] (Rehasher-eq-985:) eq-985 completed join in 30 milliseconds!
> 
> 3. A put comes in to eq-985 who decides recipients are [eq-985, eq-985]. Most likely, the hash falled somewhere between 109 and 10032 and since owners are 2, it took the next 2:
> 2010-05-06 17:54:12,307 5279  TRACE [org.infinispan.remoting.rpc.RpcManagerImpl] (HotRodServerWorker-2-1:) eq-985 broadcasting call PutKeyValueCommand{key=CacheKey{data=ByteArray{size=9, hashCode=d28dfa, array=[-84, -19, 0, 5, 116, 0, 2, 107, 48, ..]}}, value=CacheValue{data=ByteArray{size=9, array=[-84, -19, 0, 5, 116, 0, 2, 118, 48, ..]}, version=281483566645249}, putIfAbsent=false, lifespanMillis=-1000, maxIdleTimeMillis=-1000} to recipient list [eq-985, eq-985]
> 
> Everything afterwards is a mess:
> 
> 4. JGroups removes the local address from the destination. The reason Infinispan does not do it it's because the number of recipients is 2 and the number of members in the cluster 2, so it thinks it's a broadcast:
> 2010-05-06 17:54:12,308 5280  TRACE [org.infinispan.remoting.transport.jgroups.CommandAwareRpcDispatcher] (HotRodServerWorker-2-1:) real_dests=[eq-985]
> 
> 5. JGroups still sends it as a broadcast:
> 2010-05-06 17:54:12,308 5280  TRACE [org.jgroups.protocols.TCP] (HotRodServerWorker-2-1:) sending msg to null, src=eq-985, headers are RequestCorrelator: id=201, type=REQ, id=12, rsp_expected=true, NAKACK: [MSG, seqno=5], TCP: [channel_name=Infinispan-Cluster]
> 
> 6. Another node deals with this and replies:
> 2010-05-06 17:54:12,310 5282  TRACE [org.infinispan.remoting.transport.jgroups.CommandAwareRpcDispatcher] (OOB-1,Infinispan-Cluster,eq-35426:) Attempting to execute command: SingleRpcCommand{cacheName='___defaultcache', command=PutKeyValueCommand{key=CacheKey{data=ByteArray{size=9, hashCode=43487e, array=[-84, -19, 0, 5, 116, 0, 2, 107, 48, ..]}}, value=CacheValue{data=ByteArray{size=9, array=[-84, -19, 0, 5, 116, 0, 2, 118, 48, ..]}, version=281483566645249}, putIfAbsent=false, lifespanMillis=-1000, maxIdleTimeMillis=-1000}} [sender=eq-985]
> ...
> 
> 7. However, no replies yet from eq-985, so u get:
> 2010-05-06 17:54:27,310 20282 TRACE [org.infinispan.remoting.transport.jgroups.CommandAwareRpcDispatcher] (HotRodServerWorker-2-1:) responses: [sender=eq-985, retval=null, received=false, suspected=false]
> 
> 2010-05-06 17:54:27,313 20285 TRACE [org.infinispan.remoting.rpc.RpcManagerImpl] (HotRodServerWorker-2-1:) replication exception: 
> org.infinispan.util.concurrent.TimeoutException: Replication timeout for eq-985
> 
> Now, I don't understand the reason for creating a hash 10032=eq-985, 10033=eq-985. Shouldn't keeping 10032=eq-985 be enough? Why add 10033=eq-985?
> 
> Assuming there was a valid case for it, a naive approach would be to discard a second node that points to the an address already in the recipient list. So, 10032=eq-985 would be accepted for the list but when encountering 10033=eq-985, this would be skipped.
> 
> Finally, I thought waiting for rehashing to finish would solve the issue but as u can see in 2., rehashing finished and the hash is still in the same shape. Also, I've attached a log file.
> 
> Cheers,
> --
> Galder Zamarreño
> Sr. Software Engineer
> Infinispan, JBoss Cache
> <bad2_jgroups-infinispan.log.zip>_______________________________________________
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--
Manik Surtani
manik at jboss.org
Lead, Infinispan
Lead, JBoss Cache
http://www.infinispan.org
http://www.jbosscache.org