Comment #12 on issue 157 by [email protected]: Instrumenting memcached
with sFlow
http://code.google.com/p/memcached/issues/detail?id=157
@Rosso
I have no new information to share. I recently offered to shrink the sFlow
patch down to bare essentials, but got no reply yet.
I suspect the committers are focused on stability, and so anything that
adds new code is on the back burner. I recently offered
to shrink the sFlow patch down in case that helps, but got no reply yet.
So in the mean time, if you need the sFlow feature ported to 1.4.15 then
let me know.
---000---
As an aside, the version you are using also contains an
experimental "stats htwalk" command:
stats htwalk <start-offset> <N> <max-bytes>
It simply walks along the top of the hash table buckets pulling out up to N
associations and sending
back some details on them:
<record-number> <bucket-number> <secs-since-set> <secs-to-expire>
<value-bytes> <key>
The value of this measurement is that you can run it against one node and
it approximates a random sample of the
keys in the entire cluster. It therefore complements the sFlow
transaction sampling: while the sFlow sampling can
tell you the hot keys and missed keys that are active now, this
measurement allows you to survey the "dark matter"
of keys that might be occupying the cache even if they are not being
actively get or set. The measurement is light
enough that you could run it in production with no impact, and repeat it
several times to different nodes or with
different values of <start-offset> to get a larger N.
The <max-bytes> is limited to 2000000, and there are no filtering
options. That puts an upper bound on the
number of cycles it can possibly take.
Does this sound useful? If you want to try it then please test it
thoroughly in the lab first. I haven't looked at it
in a while and I'm not confident that I got the mutex locking right. All
possible disclaimers, etc.
Neil
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