[rrd-developers] RRDcached chaining mode

Steve Shipway s.shipway at auckland.ac.nz
Mon Oct 4 06:23:41 CEST 2010

Attached is a small patch for rrdtool to allow chaining of update requests received via rrdcached on to a second instance of rrdcached specified by a command line parameter -C.

$ rrdcached -l unix:/tmp/a.sock -b /var/rrda
$ rrdcached -l unix:/tmp/b.sock -b /var/rrdb -C unix:/tmp/a.sock
$ rrdtool update --daemon unix:/tmp/b.sock foo.rrd N:1:1

This updates foo.rrd in both /var/rrdb and /var/rrda, provided it exists, of course.  This also works over TCP sockets, and you can mix and match UNIX and TCP sockets if you like.  This patch only chains UPDATE requests, not CREATEs, STATs, or anything else.

The requests are sent to the remote daemon immediately after they are added to the update queue for the receiving daemon (thus avoiding any trouble of how to handle them after queueing).  If the relay fails then an error is logged BUT the rrdcached still returns a success code to the remote client (as there is no 'warning' code for a partial success).

I've run this here for a few days keeping a shadow copy of our secondary MRTG server's RRD files, and it worked without problem.  There was a bit of an issue when I defined two instances to chain to each other, though :)

I think it would need to have CREATE, and probably FLUSH, FLUSHALL and STATS chained as well for this to be of real use.



Steve Shipway
ITS Unix Services Design Lead
University of Auckland, New Zealand
Floor 1, 58 Symonds Street, Auckland
Phone: +64 (0)9 3737599 ext 86487
DDI: +64 (0)9 924 6487
Mobile: +64 (0)21 753 189
Email: s.shipway at auckland.ac.nz<mailto:s.shipway at auckland.ac.nz>
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