The write path (not replicate on write) for counters involves a read,

I'm afraid you got it wrong. The read done during counter writes *is* done by the replicate on write taks. Though really, the replicate on write taks are just one part of the counter write path (they are not "not the write path").

--
Sylvain



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