Distribution of data based on traffic

Darryl Kuhn Darryl.Kuhn at skinit.com
Sat Dec 2 02:29:01 UTC 2006

We've been running memcached in our production environment for several
weeks now quite successfully but have noticed that volume of internal
traffic on our servers is quite unevenly distributed, varying anywhere
from 2-3Mbps up to 30Mbps. After looking into it a bit it was clear to
us that this was a result memcached gets. What we're finding is that
since a key is only stored on one server, keys with values that are
large, or more often the case values that are accessed frequently cause
one server to be accessed quite a bit more than others.
We can't put a key in more than one spot (nor do we want to), but the
more I've thought about it the more I believe that there might be some
value in a mechanism that self adjusts key locations by moving heavily
trafficked keys to less heavily trafficked servers. 
Say for example that 10 keys are accessed every page request and the
hashing mechanism puts all 10 keys on a single server (say out of a pool
of 10 memcached servers). Over time (based on access rates or some other
suitable metric) this mechanism would ensure that those 10 keys are
evenly distributed across all 10 memcached instances leveling off
network traffic.
It's a thought at any rate - has anyone else dealt with this kind of
Darryl Kuhn
Chief Technology Officer
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