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From "Hiller, Dean" <>
Subject index_interval memory savings in our case(if you are curious)Š (and performance result)...
Date Wed, 20 Mar 2013 12:54:08 GMT
Oh, and to give you an idea of memory savings, we had a node at 10G RAM
usage...we had upped a few nodes to 16G from 8G as we don't have our new
nodes ready yet(we know we should be at 8G but we would have a dead
cluster if we did that).

On startup, the initial RAM is around 6-8G.  Startup with
index_interval=512 resulted in a 2.5G-2.8G initial RAM and I have seen it
grow to 3.3G and back down to 2.8G.  We just rolled this out an hour ago.
Our website response time is the same as before as well.

We rolled to only 2 nodes(out of 6) in our cluster so far to test it out
and let it soak a bit.  We will slowly roll to more nodes monitoring the
performance as we go.  Also, since dynamic snitch is not working with
SimpleSnitch, we know that just one slow node affects our website(from
personal pain/experience of nodes hitting RAM limit and slowing down
causing website to get real slow).


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 typicalŠblah blah is
>>at 0.85, doing memory cleanup which is not exactly GC but cassandra
>>managementŠ..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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