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From Paul Cichonski <>
Subject RE: heavy insert load overloads CPUs, with MutationStage pending
Date Wed, 11 Sep 2013 16:46:00 GMT
How much of the data you are writing is going against the same row key? 

I've experienced some issues using CQL to write a full wide-row at once (across multiple threads)
that exhibited some of the symptoms you have described (i.e., high cpu, dropped mutations).

This question goes into it a bit more:
. I was able to solve my issue by switching to using the thrift batch_mutate to write a full
wide-row at once instead of using many CQL INSERT statements. 


> -----Original Message-----
> From: Keith Freeman []
> Sent: Wednesday, September 11, 2013 9:16 AM
> To:
> Subject: Re: heavy insert load overloads CPUs, with MutationStage pending
> On 09/10/2013 11:42 AM, Nate McCall wrote:
> > With SSDs, you can turn up memtable_flush_writers - try 3 initially (1
> > by default) and see what happens. However, given that there are no
> > entries in 'All time blocked' for such, they may be something else.
> Tried that, it seems to have reduced the loads a little after everything
> warmed-up, but not much.
> >
> > How are you inserting the data?
> A java client on a separate box using the datastax java driver, 48 threads
> writing 100 records each iteration as prepared batch statements.
> At 5000 records/sec, the servers just can't keep up, so the client backs up.
> That's only 5M of data/sec, which doesn't seem like much.  As I mentioned,
> switching to SSDs didn't help much, so I'm assuming at this point that the
> server overloads are what's holding up the client.

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