When an operation takes more than "slowms" milliseconds to complete, we print it "slow query" log for this operations.

However, sometimes a long-running queries that don't complete (due to server OOMing for example), won't show up in logs.

Let's introduce some kind of "slow in-progress query" log for this kind of operations. 

This might contain less information than slow query log on completion because some statistics are collected after the operation is complete.