[munin-users] GraphOld.pm: bug with cdef, workaround via get_field_name()

[Mrten <mrt...@ii...>]

There is a bug in GraphOld.pm triggered by the trimming in get_field_name() 
in GraphOld.pm that fucks up generating DEFs when the variable name is > 15 characters:

multigraph mysql_wsrep_avgwritesetbytes
graph_args --base 1000 --no-gridfit --slope-mode
graph_title Galera writesets average bytes
graph_category mysql
wsrep_replicated.draw LINE1
wsrep_replicated.min 0
wsrep_replicated.type DERIVE
wsrep_replicated.graph no
wsrep_received.draw LINE1
wsrep_received.min 0
wsrep_received.type DERIVE
wsrep_received.graph no
wsrep_replicated_bytes.draw LINE1
wsrep_replicated_bytes.min 0
wsrep_replicated_bytes.type DERIVE
wsrep_replicated_bytes.graph no
wsrep_received_bytes.draw LINE1
wsrep_received_bytes.min 0
wsrep_received_bytes.type DERIVE
wsrep_received_bytes.graph no
wsrep_avgreplicated.cdef wsrep_replicated_bytes,wsrep_replicated,/
wsrep_avgreplicated.draw LINE1
wsrep_avgreplicated.min 0
wsrep_avgreplicated.label average size of sent writeset
wsrep_avgreplicated.type DERIVE
wsrep_avgreceived.cdef wsrep_received_bytes,wsrep_received,/
wsrep_avgreceived.draw LINE1
wsrep_avgreceived.min 0
wsrep_avgreceived.label average size of received writeset
wsrep_avgreceived.type DERIVE

generated 

'DEF:awsrep_received=/var/lib/munin/virtual/database-3-mysql_wsrep_avgwritesetbytes-wsrep_received-d.rrd:42:MAX' \
'DEF:iwsrep_received=/var/lib/munin/virtual/database-3-mysql_wsrep_avgwritesetbytes-wsrep_received-d.rrd:42:MIN' \
'DEF:gwsrep_received=/var/lib/munin/virtual/database-3-mysql_wsrep_avgwritesetbytes-wsrep_received-d.rrd:42:AVERAGE' \
'CDEF:a510ac46cd6faa32=awsrep_replicated_bytes,awsrep_replicated,/' \
'CDEF:i510ac46cd6faa32=iwsrep_replicated_bytes,iwsrep_replicated,/' \
'CDEF:g510ac46cd6faa32=gwsrep_replicated_bytes,gwsrep_replicated,/' \

(notice missing DEFs)

Now, if I change the 15's in this function to '115' (255 would be better, that's
rrdtool's limit on vnames):


sub get_field_name {
    my $name = shift;

    $name = substr(Digest::MD5::md5_hex($name), -15)
        if (length $name > 15);

    return $name;
}

I get a graph that works. I realize it's a hack, but there's probably a few hard to 
find bugs here regarding variable name consistency in CDEFs (see also bugs 1017 and 578:
http://munin-monitoring.org/ticket/578 )

M.