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From "Rob Davies (JIRA)" <j...@apache.org>
Subject [jira] Resolved: (AMQ-1925) JDBC-Master/Slave Failover - Consumer stop after 1000 Messages
Date Wed, 10 Sep 2008 18:06:52 GMT

     [ https://issues.apache.org/activemq/browse/AMQ-1925?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Rob Davies resolved AMQ-1925.
-----------------------------

    Resolution: Fixed

Patch applied in SVN revision 693915.

> JDBC-Master/Slave Failover - Consumer stop after 1000 Messages
> --------------------------------------------------------------
>
>                 Key: AMQ-1925
>                 URL: https://issues.apache.org/activemq/browse/AMQ-1925
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.1.0
>            Reporter: Mario Siegenthaler
>            Assignee: Rob Davies
>             Fix For: 5.3.0
>
>         Attachments: AMQ1925Test.java, heapdump-1220373534484.hprof, patch-1925-1.diff,
threaddump-1220371256910.tdump
>
>
> In a JDBC-Master/Slave Environment with ActiveMQ 5.1.0 (+patches for 1710 und 1838) the
failover for consumers works, the consumers resume to get messages after the failover but
then the suddenly stop after approx. 1000 messages (mostly 1000, one got to 1080). The consumers
are using transacted sessions.
> The thread dump look unsuspicious, everybody is waiting on the Socket
>    java.lang.Thread.State: RUNNABLE
> 	at java.net.SocketInputStream.socketRead0(Native Method)
> 	at java.net.SocketInputStream.read(SocketInputStream.java:129)
> 	at org.apache.activemq.transport.tcp.TcpBufferedInputStream.fill(TcpBufferedInputStream.java:50)
> 	at org.apache.activemq.transport.tcp.TcpBufferedInputStream.read(TcpBufferedInputStream.java:58)
> 	at java.io.DataInputStream.readInt(DataInputStream.java:370)
> 	at org.apache.activemq.openwire.OpenWireFormat.unmarshal(OpenWireFormat.java:269)
> 	at org.apache.activemq.transport.tcp.TcpTransport.readCommand(TcpTransport.java:203)
> 	at org.apache.activemq.transport.tcp.TcpTransport.doRun(TcpTransport.java:195)
> 	at org.apache.activemq.transport.tcp.TcpTransport.run(TcpTransport.java:183)
> 	at java.lang.Thread.run(Thread.java:619)
> A memory dump from the consumers shows that they've really run out of messages and are
waiting for the broker to deliver new ones. I've attached both the thread dump and the heap
dump to this issue (or better: I'll do so :)
> The broker doesn't do anything (also waits on the transport-socket), the queue has a
full page-in buffer (100 messages) but obviously fails to do anything with it. If I manually
trigger a doDispatch of all pagedIn messages (via the debugger, just a try to revive the thing)
it returns doing nothing at all, since all subscriptions are full (s.isFull). I further investigated
the issue and was confused to see the prefetchExtension field of the PrefetchSubscription
having a value of -1000 (negative!). This explains why it was considered full:
>   dispatched.size() - prefetchExtension >= info.getPrefetchSize()
>   0 - (-1000) >= 1000
> quite nasty.. so even though the dispatched size was zero the client didn't receive any
new messages.
> The only place this value can become negative is inside acknowledge, where it's decremented
(prefetchExtension--), all other places do a Math.max(0, X).
> So here's my guess what happened: The client had a full (1000 messages) prefetch buffer
when I killed my master. As soon as the slave was done starting they reconnected and started
processing the messages in the prefetch and acknowleding them. This gradually decremented
the counter into a negative value because the slave never got a chance to increment the prefetchExtension
since it didn't action delivery those messages.
> Possible solutions:
> - clear the prefetch buffer on a failover
> - just don't allow this value to become smaller than zero (not sure if that covers all
bases)

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