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From "James Lee (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-5789) Data not fully replicated with 2 nodes and replication factor 2
Date Wed, 07 Aug 2013 13:52:48 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-5789?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

James Lee updated CASSANDRA-5789:
---------------------------------

    Attachment: CassBugRepro.py

Repro script for the bug, run it as follows:
-- The script assumes you have two-node Cassandra cluster set up and running.
-- The system running the test should have Python (I used 2.7) with pycassa installed.
-- Run the setup stage as follows: "python CassBugRepro.py -c ip1,ip2 -s -f".  This creates
keyspaces and writes 2M rows into them.
-- Once the above has completed, wait until all hints have been delivered (I checked using
nodetool).
-- Then run the next stage which does random read/writes: "python CassBugRepro.py -c ip1,ip2
-r".
-- If the bug has been repro'd, you'll see output like "NotFoundException for DN 11055691";
where we haven't found something we'd previously sucessfully written.
                
> Data not fully replicated with 2 nodes and replication factor 2
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-5789
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5789
>             Project: Cassandra
>          Issue Type: Bug
>    Affects Versions: 1.2.2, 1.2.6
>         Environment: Official Datastax Cassandra 1.2.6, running on Linux RHEL 6.2.  I've
seen the same behavior with Cassandra 1.2.2.
> Sun Java 1.7.0_10-b18 64-bit
> Java heap settings: -Xms8192M -Xmx8192M -Xmn2048M
>            Reporter: James Lee
>         Attachments: CassBugRepro.py
>
>
> I'm seeing a problem with a 2-node Cassandra test deployment, where it seems that data
isn't being replicated among the nodes as I would expect.
> The setup and test is as follows:
> - Two Cassandra nodes in the cluster (they each have themselves and the other node as
seeds in cassandra.yaml).
> - Create 40 keyspaces, each with simple replication strategy and 
> replication factor 2.
> - Populate 125,000 rows into each keyspace, using a pycassa client with a connection
pool pointed at both nodes.  These are populated with writes using consistency level of 1.
> - Wait until nodetool on each node reports that there are no hinted handoffs outstanding
(see output below).
> - Do random reads of the rows in the keyspaces, again using a pycassa client with a connection
pool pointed at both nodes.  These are read using consistency level 1.
> I'm finding that the vast majority of reads are successful, but a small 
> proportion (~0.1%) are returned as Not Found.  If I manually try to look up 
> those keys using cassandra-cli, I see that they are returned when querying one of the
nodes, but not when querying the other.  So it seems like some of the rows have simply not
been replicated, even though the write for these rows was reported to the client as successful.
> If I reduce the rate at which the test tool initially writes data into the database then
I don't see any failed reads, so this seems like a load-related issue.  My understanding is
that if all writes were successful and there are no pending hinted handoffs, then the data
should be fully-replicated and reads should return it (even with read and write consistency
of 1).
> Here's the output from notetool on the two nodes:
> comet-mvs01:/dsc-cassandra-1.2.6# ./bin/nodetool tpstats
> Pool Name                    Active   Pending      Completed   Blocked  All time blocked
> ReadStage                         0         0              2         0              
  0
> RequestResponseStage              0         0         878494         0              
  0
> MutationStage                     0         0        2869107         0              
  0
> ReadRepairStage                   0         0              0         0              
  0
> ReplicateOnWriteStage             0         0              0         0              
  0
> GossipStage                       0         0           2208         0              
  0
> AntiEntropyStage                  0         0              0         0              
  0
> MigrationStage                    0         0            994         0              
  0
> MemtablePostFlusher               0         0           4399         0              
  0
> FlushWriter                       0         0           2264         0              
556
> MiscStage                         0         0              0         0              
  0
> commitlog_archiver                0         0              0         0              
  0
> InternalResponseStage             0         0            153         0              
  0
> HintedHandoff                     0         0              2         0              
  0
> Message type           Dropped
> RANGE_SLICE                  0
> READ_REPAIR                  0
> BINARY                       0
> READ                         0
> MUTATION                 87655
> _TRACE                       0
> REQUEST_RESPONSE             0
> comet-mvs02:/dsc-cassandra-1.2.6# ./bin/nodetool tpstats
> Pool Name                    Active   Pending      Completed   Blocked  All time blocked
> ReadStage                         0         0            868         0              
  0
> RequestResponseStage              0         0        3919665         0              
  0
> MutationStage                     0         0        8177325         0              
  0
> ReadRepairStage                   0         0            113         0              
  0
> ReplicateOnWriteStage             0         0              0         0              
  0
> GossipStage                       0         0           9624         0              
  0
> AntiEntropyStage                  0         0              0         0              
  0
> MigrationStage                    0         0           2666         0              
  0
> MemtablePostFlusher               0         0           7869         0              
  0
> FlushWriter                       0         0           4273         0              1179
> MiscStage                         0         0              0         0              
  0
> commitlog_archiver                0         0              0         0              
  0
> InternalResponseStage             0         0            215         0              
  0
> HintedHandoff                     0         0              8         0              
  0
> Message type           Dropped
> RANGE_SLICE                  0
> READ_REPAIR                  0
> BINARY                       0
> READ                         0
> MUTATION                531988
> _TRACE                       0
> REQUEST_RESPONSE             0

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