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From "Hiller, Dean" <>
Subject Re: Cassandra freezes
Date Wed, 20 Mar 2013 12:48:55 GMT
Yup, we are rolling it slowly.  In production, we have 2 nodes out of 6
switched already and so far have no website degredation at all.  We have
narrow rows as well and as the comment says in the props file, "if you
have narrow rows going to 512 sometimes has no impact on performance" and
in our case so far that seems to be true, but we are still monitoring
before rolling to other nodes in production.

(we have 10 billion rows on 6 servers and RAM was killing us until this
change and if this works out, we should be able to go to 20 or 30 billion
per 6 computers).  We are also adding 12 nodes as well to our 6 node
cluster but I wanted to test this out to see if I could increase rows per
node in our cluster.

Time will tell as we soak the two nodes in production and then roll on
more nodes to this fix.


On 3/20/13 6:41 AM, "Andras Szerdahelyi"
<> wrote:

>2. Upping index_interval from 128 to 512 (this seemed to reduce our memory
>usage significantly!!!)
>I'd be very careful with that as a one-stop improvement solution for two
>reasons AFAIK
>1) you have to rebuild stables ( not an issue if you are evaluating, doing
>test writes.. Etc, not so much in production )
>2) it can affect reads ( number of sstable reads to serve a read )
>especially if your key/row cache is ineffective
>On 20/03/13 13:34, "Hiller, Dean" <> wrote:
>>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
>>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
>>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 "..
>>>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
>>>So commit log and data directory is (probably) on the same drive.
>>>Best regards,
>>>Joel Samuelsson

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