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From Mohica Jasha <mohica.ja...@gmail.com>
Subject Re: query deadlock(?) after flushing a table
Date Mon, 01 Jul 2013 23:51:00 GMT
the cql scripts and the thread dump attached.

Thanks in advance.


On Mon, Jul 1, 2013 at 7:41 PM, Mohica Jasha <mohica.jasha@gmail.com> wrote:

> Hey,
>
> I created a table with a wide row. Query on the wide row after removing
> the entries and flushing the table becomes very slow. I am aware of the
> impact of tombstones but it seems that there is a deadlock which prevents
> the query to be completed.
>
> step by step:
>
> 1. creating the keyspace and the table:
>
> CREATE KEYSPACE test WITH replication = {'class': 'SimpleStrategy',
> 'replication_factor': '1'};
> use test;
> CREATE TABLE job_index (   stage text,   "timestamp" text,   PRIMARY KEY
> (stage, "timestamp") ) WITH gc_grace_seconds=10 AND
> compaction={'sstable_size_in_mb': '10', 'class':
> 'LeveledCompactionStrategy'};
>
> 2. insert 5000 entries to the job_index column family using the attached
> script (insert_1-5000.cql)
>
> 3. flushing the table:
> nodetool flush test job_index
>
> 4. delete the 5000 entries in the wide row using the attached script
> (delete_1-5000.cql)
>
> so far the queries return all the entries in the wide row in a fraction of
> a second.
>
> 5. flushing the table:
> nodetool flush test job_index
>
> 6. run the following query:
> cqlsh:test> SELECT * from job_index limit 1 ;
> Request did not complete within rpc_timeout.
>
> The execution of the query gets blocked and eventually the query times out.
>
> In the cassandra's log file I see the following lines:
>
> DEBUG [ScheduledTasks:1] 2013-07-01 19:10:39,469 GCInspector.java (line
> 121) GC for ParNew: 16 ms for 5 collections, 754590496 used; max is
> 2093809664
> DEBUG [ScheduledTasks:1] 2013-07-01 19:10:40,473 GCInspector.java (line
> 121) GC for ParNew: 19 ms for 6 collections, 547894840 used; max is
> 2093809664
> DEBUG [ScheduledTasks:1] 2013-07-01 19:10:41,475 GCInspector.java (line
> 121) GC for ParNew: 16 ms for 5 collections, 771812864 used; max is
> 2093809664
>
> A few minutes later after the compaction finishes the problem goes away.
>
> I am using cassandra 1.2.6.
> I tested on Linux (CentOS) and MacOS and I get the same result!
>
> Is this a known issue?
>
>
>

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