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?

Andrew


On Wed, Jul 3, 2013 at 1:03 PM, Robert Coli <rcoli@eventbrite.com> wrote:
On Wed, Jul 3, 2013 at 9:59 AM, Andrew Bialecki <andrew.bialecki@gmail.com> 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