Log slow oplog queries (mplotqueries --oplog)

[mitesh-gosavi]

Expected behavior

mplotqueries —oplog flag should provide a scatterplot of all the slow oplog entries along with their duration and timestamp. The scatterplot should be grouped or can be left ungrouped based on additional parameters (if available)

Actual/current behavior

mTools does not currently log any oplogs for the secondary replica set. This issue focuses on logging the slow oplog operations. Log lines for slow oplogs were added as a fix in versions 4.1.5, 3.6.11, 4.0.6 (For reference, see SERVER-32146). mTools currently skips these lines and does not parse or plot them.

Steps to reproduce the actual/current behaviour

mplotqueries —oplog flag can be added to the argument parser. The parser on receiving the --oplog flag can search for log lines containing the “applied op” token (for reference, see https://docs.mongodb.com/manual/core/replica-set-oplog/). On encountering the token, the parser can use the built-in duration function to parse the duration and plot it on a scatterplot. For more accuracy, the parser can also verify if the operation in the log line is an “REPL” operation (for reference, see https://docs.mongodb.com/manual/core/replica-set-oplog/).

Environment

Software	Version
mtools	1.5.3
MongoDB server	4.0.10