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From Peter Schuller <peter.schul...@infidyne.com>
Subject Re: Meaning of values in tpstats
Date Sat, 10 Dec 2011 18:59:34 GMT
> Pool Name                    Active   Pending      Completed   Blocked
 All
> time blocked
> ReadStage                        27      2166     3565927301      
  0

In general, "active" refers to work that is being executed right now,
"pending" refers to work that is waiting to be executed (go into
"active"), and completed is the cumulative all-time (since node start)
count of the number of tasks executed.

With the slicing, I'm not sure off the top of my head. I'm sure
someone else can chime in. For e.g. a multi-get, they end up as
independent tasks.

Typically having pending persistently above 0 for ReadStage or
MutationStage, especially if more than a hand-ful, means that you are
having a performance issue - either capacity problem or something
else, as incoming requests will have to wait to be services. Typically
the most common effect is that you are bottlenecking on I/O and
ReadStage pending shoots through the roof.

There are exceptions. If you e.g. submit a really large multi-get of
5000, that will naturally lead to a spike (and if all 5000 of them
need to go down to disk, the spike will survive for a bit). If you are
ONLY doing these queries, that's not a problem per se. But if you are
also expecting other requests to have low latency, then you want to
avoid it.

In general, batching is good - but don't overdo it, especially for
reads, and especially if you're going to disk for the workload.

-- 
/ Peter Schuller (@scode, http://worldmodscode.wordpress.com)

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