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From "Aaron Morton (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-4223) Non Unique Streaming session ID's
Date Sun, 06 May 2012 23:10:48 GMT
Aaron Morton created CASSANDRA-4223:
---------------------------------------

             Summary: Non Unique Streaming session ID's
                 Key: CASSANDRA-4223
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4223
             Project: Cassandra
          Issue Type: Bug
          Components: Core
    Affects Versions: 1.0.9
         Environment: Ubuntu 10.04.2 LTS

java version "1.6.0_24"
Java(TM) SE Runtime Environment (build 1.6.0_24-b07)
Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02, mixed mode)

"Bare metal" servers from https://www.stormondemand.com/servers/baremetal.html 
The servers run on a custom hypervisor.
 
            Reporter: Aaron Morton
            Assignee: Aaron Morton


I have observed repair processes failing due to duplicate Streaming session ID's. In this
installation it is preventing rebalance from completing. I believe it has also prevented repair
from completing in the past. 

The attached streaming-logs.txt file contains log messages and an explanation of what was
happening during a repair operation. it has the evidence for duplicate session ID's.

The duplicate session id's were generated on the repairing node and sent to the streaming
node. The streaming source replaced the first session with the second which resulted in both
sessions failing when the first FILE_COMPLETE message was received. 

The errors were:

{code:java}
DEBUG [MiscStage:1] 2012-05-03 21:40:33,997 StreamReplyVerbHandler.java (line 47) Received
StreamReply StreamReply(sessionId=26132848816442266, file='/var/lib/cassandra/data/FMM_Studio/PartsData-hc-1-Data.db',
action=FILE_FINISHED)
ERROR [MiscStage:1] 2012-05-03 21:40:34,027 AbstractCassandraDaemon.java (line 139) Fatal
exception in thread Thread[MiscStage:1,5,main]
java.lang.IllegalStateException: target reports current file is /var/lib/cassandra/data/FMM_Studio/PartsData-hc-1-Data.db
but is null
        at org.apache.cassandra.streaming.StreamOutSession.validateCurrentFile(StreamOutSession.java:195)
        at org.apache.cassandra.streaming.StreamReplyVerbHandler.doVerb(StreamReplyVerbHandler.java:58)
        at org.apache.cassandra.net.MessageDeliveryTask.run(MessageDeliveryTask.java:59)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
{code}

and

{code:java}
DEBUG [MiscStage:2] 2012-05-03 21:40:36,497 StreamReplyVerbHandler.java (line 47) Received
StreamReply StreamReply(sessionId=26132848816442266, file='/var/lib/cassandra/data/OpsCenter/rollups7200-hc-3-Data.db',
action=FILE_FINISHED)
ERROR [MiscStage:2] 2012-05-03 21:40:36,497 AbstractCassandraDaemon.java (line 139) Fatal
exception in thread Thread[MiscStage:2,5,main]
java.lang.IllegalStateException: target reports current file is /var/lib/cassandra/data/OpsCenter/rollups7200-hc-3-Data.db
but is null
        at org.apache.cassandra.streaming.StreamOutSession.validateCurrentFile(StreamOutSession.java:195)
        at org.apache.cassandra.streaming.StreamReplyVerbHandler.doVerb(StreamReplyVerbHandler.java:58)
        at org.apache.cassandra.net.MessageDeliveryTask.run(MessageDeliveryTask.java:59)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
{code}


I think this is because System.nanoTime() is used for the session ID when creating the StreamInSession
objects (driven from StorageService.requestRanges()) . 

>From the documentation (http://docs.oracle.com/javase/6/docs/api/java/lang/System.html#nanoTime())


{quote}
This method provides nanosecond precision, but not necessarily nanosecond accuracy. No guarantees
are made about how frequently values change. 
{quote}

Also some info here on clocks and timers https://blogs.oracle.com/dholmes/entry/inside_the_hotspot_vm_clocks

The hypervisor may be at fault here. But it seems like we cannot rely on successive calls
to nanoTime() to return different values. 

To avoid message/interface changes on the StreamHeader it would be good to keep the session
ID a long. The simplest approach may be to make successive calls to nanoTime until the result
changes. We could fail if a certain number of milliseconds have passed. 

Hashing the file names and ranges is also a possibility, but more involved. 

(We may also want to drop latency times that are 0 nano seconds.)


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