Explain what you would like to see improved

Performance counters (e.g., total bytes written, wall clock spent writing, etc.) should be added to the RPageSinkFile and RPageSinkDaos classes. The bare minimum should allow to compute the write throughput.

Optional: share how it could be improved

In particular, four new RCounters will be added: szWritePayload, timeWallWrite, timeWallZip, timeCpuWrite, timeCpuZip.