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From Jonathan Ellis <>
Subject Re: Batch writes getting slow
Date Thu, 06 Oct 2011 16:15:42 GMT
On Thu, Oct 6, 2011 at 10:53 AM, Stefan Reek <> wrote:
> We do have the commitlogs on separate devices, are there any other basics
> that I could have forgotten, or
> any parameters that are important for write performance?

1.0 write performance is something like 30% better...  I don't think
there's anything else you'll find for "free."

> As I understand it
> the flush thresholds mainly
> influence read performance instead of write performance.

It can affect write performance if you're flushing really small
sstables, but I doubt that's the problem here.

> Would it make any difference to write the data with more threads from the
> client, as that's something we can easily tune.

Not in this case because Cassandra turns the batch into single-row
writes internally, so it gets parallelized that way.

If you can avoid waiting for One Big Batch and stream changes in as
they happen, that would help.

> I can see the sawtooth in the JVM only for Par Eden and Par Survivor space,
> the CMS Old Gen space just keeps on growing though.

Is it actually filling up enough to trigger an old-gen CMS gc?

Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support

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