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https://issues.apache.org/jira/browse/CASSANDRA-4223?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13272704#comment-13272704
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Aaron Morton commented on CASSANDRA-4223:
-----------------------------------------
There are two path ways for a StreamOutSession to be added to the SOS.streams
map:
1) Push / transfer. When node A wants to push data to node B using
StreamOut.transferRanges(). In this case the SOS context using the target ip
address - <node_b_ip, node_a_sos_counter>
2) Pull / request. When node B wants node A to send it data, using
StreamIn.requestRanges(). Node B creates a StreamInSession that uses the target
ip address - <node_a_ip, node_b_sis_counter>. When node A gets the stream
request from node b it creates a StreamOutSession with context <node_b_ip,
node_b_sis_counter>
So we can end up with these two sos contexts on node A:
* <node_b_ip, node_a_sos_counter>
* <node_b_ip, node_b_sis_counter>
We need to avoid collisions between node_a_sos_counter and node_b_sis_counter.
It's an unlikely event but we need to be safe.
Adding the source_flag means we end up with this on node A:
* <node_b_ip, 1 "push", node_a_sos_counter>
* <node_b_ip, 0 "pull", node_b_sis_counter>
bq. Isn't it enough to just increment AtomicLong counter until there is no
collision when creating locally?
Are you saying "lock around creating the StreamOutSessions from both code paths
and create session ID's that do not collide with known session ids ?"
> 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
> 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
> Labels: datastax_qa
> Fix For: 1.0.11, 1.1.1
>
> Attachments: 4223_counter_session_id.diff, NanoTest.java, fmm
> streaming bug.txt
>
>
> 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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