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From Andrew Bialecki <>
Subject Re: Lots of replicate on write tasks pending, want to investigate
Date Wed, 03 Jul 2013 21:43:34 GMT
Can someone remind me why replicate on write tasks might be related to the
high disk I/O? My understanding is the replicate on write involves sending
the update to other nodes, so it shouldn't involve any disk activity --
disk activity would be during the mutation/write phase.

The write path (not replicate on write) for counters involves a read, so
that explains the high disk I/O, but for that I'd expect to see many write
requests pending (which we see a bit), but not replicate on writes backing
up. What am I missing?


On Wed, Jul 3, 2013 at 1:03 PM, Robert Coli <> wrote:

> On Wed, Jul 3, 2013 at 9:59 AM, Andrew Bialecki <
> > wrote:
>> 2. I'm assuming in our case the cause is incrementing counters because
>> disk reads are part of the write path for counters and are not for
>> appending columns to a row. Does that logic make sense?
> That's a pretty reasonable assumption if you are not doing any other reads
> and you see your disk busy doing non-compaction related reads. :)
> =Rob

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