More updater stats

We have some great information about what the updater has updated, however we have no details on how much work it did to do those updates i.e: how many documents it read, how big are those documents were and how much data it wrote. As a result it is hard to tell if there is a performance issue with the updater itself or the hardware underneath.

Here are some suggestions on new stats that I think might be useful (I do not know the code so these might be silly suggestions):

time spent reading data from disk
time spent processing in the v8 engine
time spent writing data to disk
amount of data read from disk
amount of data written to disk
number of documents read/processed

What the current stats look like:

[couchdb:info,2014-09-20T21:04:07.105,ns_1@10.0.0.1:<0.17156.6231>:couch_log:info:39]Set view `Patrick`, main group `_design/dev_test`, updater finished

Indexing time: 0.119 seconds

Blocked time:  0.000 seconds

Inserted IDs:  1

Deleted IDs:   4

Inserted KVs:  1

Deleted KVs:   1

Cleaned KVs:   0

# seqs done:   5