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From Mark Hahn <m...@hahnca.com>
Subject how to debug a single PUT that is very slow?
Date Mon, 02 Apr 2012 06:41:16 GMT
I'm having a problem in a particular situation where a specific put of a
new document is taking 10 to 20 seconds.  The db is not very loaded down.
 There are 5 to 25 writes/sec and about 200 reads per second.  I have a db
watcher that is invoked on every change.

Looking at the log timestamps, the PUT for the new document doesn't even
register as an [info] line until ten seconds after my app sent the http
request.  The log just shows normal read and writes during that 10 seconds.
 No view is being rebuilt nor is there a compaction happening.

I can repeat this any time I want by uploading 18 files from my browser,
where each of the 18 triggers an invocation of imagemagick thumbnail
conversion and then adding that thumbnail as an attachment to each of 18
docs.  The attachments are only about 20 kbytes each.  The doc that is
trying to be created is unrelated to any of those 18.  The problem just
happens when I try to create the doc at the same time.

The cpu is not loaded.  Node and the db are only consuming about 15% each
of the cpu during the episode.

Any idea what could cause this?  What can I do to track the problem down?

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