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From Dominic Letz <dominicl...@exosite.com>
Subject Re: C* throws OOM error despite use of automatic paging
Date Tue, 13 Jan 2015 05:09:57 GMT
Does your use case include many tombstones? If yes then that might explain
the OOM situation.

If you want to know for sure you can enable the heap dump generation on
crash in cassandra-env.sh just uncomment JVM_OPTS="$JVM_OPTS
-XX:+HeapDumpOnOutOfMemoryError" and then run your query again. The
heapdump will have the answer.




On Tue, Jan 13, 2015 at 10:54 AM, Mohammed Guller <mohammed@glassbeam.com>
wrote:

>  The heap usage is pretty low ( less than 700MB) when the application
> starts. I can see the heap usage gradually climbing once the application
> starts. C* does not log any errors before OOM happens.
>
>
>
> Data is on EBS. Write throughput is quite high with two applications
> simultaneously pumping data into C*.
>
>
>
>
>
> Mohammed
>
>
>
> *From:* Ryan Svihla [mailto:rs@foundev.pro]
> *Sent:* Monday, January 12, 2015 3:39 PM
> *To:* user
>
> *Subject:* Re: C* throws OOM error despite use of automatic paging
>
>
>
> I think it's more accurate that to say that auto paging prevents one type
> of OOM. It's premature to diagnose it as 'not happening'.
>
>
>
> What is heap usage when you start? Are you storing your data on EBS? What
> kind of write throughput do you have going on at the same time? What errors
> do you have in the cassandra logs before this crashes?
>
>
>
>
>
> On Sat, Jan 10, 2015 at 1:48 PM, Mohammed Guller <mohammed@glassbeam.com>
> wrote:
>
> nodetool cfstats shows 9GB. We are storing simple primitive value. No
> blobs or collections.
>
>
>
> Mohammed
>
>
>
> *From:* DuyHai Doan [mailto:doanduyhai@gmail.com]
> *Sent:* Friday, January 9, 2015 12:51 AM
> *To:* user@cassandra.apache.org
> *Subject:* Re: C* throws OOM error despite use of automatic paging
>
>
>
> What is the data size of the column family you're trying to fetch with
> paging ? Are you storing big blob or just primitive values ?
>
>
>
> On Fri, Jan 9, 2015 at 8:33 AM, Mohammed Guller <mohammed@glassbeam.com>
> wrote:
>
> Hi –
>
>
>
> We have an ETL application that reads all rows from Cassandra (2.1.2),
> filters them and stores a small subset in an RDBMS. Our application is
> using Datastax’s Java driver (2.1.4) to fetch data from the C* nodes. Since
> the Java driver supports automatic paging, I was under the impression that
> SELECT queries should not cause an OOM error on the C* nodes. However, even
> with just 16GB data on each nodes, the C* nodes start throwing OOM error as
> soon as the application starts iterating through the rows of a table.
>
>
>
> The application code looks something like this:
>
>
>
> Statement stmt = new SimpleStatement("SELECT x,y,z FROM
> cf").setFetchSize(5000);
>
> ResultSet rs = session.execute(stmt);
>
> while (!rs.isExhausted()){
>
>       row = rs.one()
>
>       process(row)
>
> }
>
>
>
> Even after we reduced the page size to 1000, the C* nodes still crash. C*
> is running on M3.xlarge machines (4-cores, 15GB). We manually increased the
> heap size to 8GB just to see how much heap C* consumes. With 10-15 minutes,
> the heap usage climbs up to 7.6GB. That does not make sense. Either
> automatic paging is not working or we are missing something.
>
>
>
> Does anybody have insights as to what could be happening? Thanks.
>
>
>
> Mohammed
>
>
>
>
>
>
>
>
>
>
>
> --
>
> Thanks,
>
> Ryan Svihla
>



-- 
Dominic Letz
Director of R&D
Exosite <http://exosite.com>

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