Create performance counter exposing compression ratio

[hkaiser]

If compressionn is enabled for parcel data it would be valuable to be able to extract the achieved compression ratios at runtime. This is to create a performance counter which exposes the achieved compression ratio (overall, and for a particular action?)

[hkaiser]

This should be implemented with a general performance counter which exposes the ratio of two other performance counters:

/arithmetics/divide@perf_counter_nominator,perf_counter_denominator

(i.e. the two base performance counters are specified as parameters to the aggregating counter).

[hkaiser]

This will be implemented with #747: Create performance counters exposing arithmetic operations

[hkaiser]

#747 has been fixed, use this counter to retrieve the compression ratio, for instance:

/arithmetics/divide@/serialize/count/tcp/sent,/data/count/tcp/sent

which will output the ratio of serialized bytes over sent bytes.