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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4223) Non Unique Streaming session ID's
Date Tue, 08 May 2012 22:13:48 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4223?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13270886#comment-13270886
] 

Jonathan Ellis commented on CASSANDRA-4223:
-------------------------------------------

Ugh, so the problem is that sometimes session IDs are generated by the target, and sometimes
by the source?  That's broken...

I think there's three possible solutions:
# always generate session IDs on the source, so our Pair really is unique [the way I thought
it worked :)]
# try to make the 64bit session IDs "unique enough" across the cluster [aaron's timestamp
+ counter]
# guarantee the session IDs are unique-per-host, and make the session context (source, id-generated-by-ip,
id) instead of just (source, id) [yuki's suggestion]
# just switch to a UUID

#4 is probably simplest, but only #2 and #3 will be backwards-compatible.  Of those two I
feel more confident about #3...  The only unique-id-in-64-bit schemas I know of require some
coordination up front among participating nodes (e.g., http://engineering.twitter.com/2010/06/announcing-snowflake.html)
                
> 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: 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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