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From "Hiller, Dean" <>
Subject Re: Cassandra freezes
Date Wed, 20 Mar 2013 12:34:49 GMT
Also, look at the cassandra logs.  I bet you see the typicalÅ blah blah is
at 0.85, doing memory cleanup which is not exactly GC but cassandra memory
managementÅ ..and of course, you have GC on top of that.

If you need to get your memory down, there are multiple ways
1. Switching size tiered compaction to leveled compaction(with 1 billion
narrow rows, this helped us quite a bit)
2. Upping index_interval from 128 to 512 (this seemed to reduce our memory
usage significantly!!!)
3. Just add more nodes as moving the rows to other servers reduces memory
from #1 and #2 above since the server would have less rows


On 3/20/13 6:29 AM, "Andras Szerdahelyi"
<> wrote:

>I'd say GC. Please fill in form CASS-FREEZE-001 below and get back to us
>:-) ( sorry )
>How big is your JVM heap ? How many CPUs ?
>Garbage collection taking long ? ( look for log lines from GCInspector)
>Running out of heap ? ( "heap is .. full" log lines )
>Any tasks backing up / being dropped ? ( nodetool tpstats and ".. dropped
>in last .. ms" log lines )
>Are writes really slow? ( nodetool cfhistograms Keyspace ColumnFamily )
>How much is lots of data? Wide or skinny rows? Mutations/sec ?
>Which Compaction Strategy are you using? Output of show schema (
>cassandra-cli ) for the relevant Keyspace/CF might help as well
>What consistency are you doing your writes with ? I assume ONE or ANY if
>you have a single node.
>What are the values for these settings in cassandra.yaml
>Which version of Cassandra?
>From:  Joel Samuelsson <>
>Reply-To:  "" <>
>Date:  Wednesday 20 March 2013 13:06
>To:  "" <>
>Subject:  Cassandra freezes
>I've been trying to load test a one node cassandra cluster. When I add
>lots of data, the Cassandra node freezes for 4-5 minutes during which
>neither reads nor writes are served.
>During this time, Cassandra takes 100% of a single CPU core.
>My initial thought was that this was Cassandra flushing memtables to the
>disk, however, the disk i/o is very low during this time.
>Any idea what my problem could be?
>I'm running in a virtual environment in which I have no control of drives.
>So commit log and data directory is (probably) on the same drive.
>Best regards,
>Joel Samuelsson

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