One piece of feedback I often hear from users of Percona Monitoring and Management (PMM) is that while the Query Analytics feature is great and provides a lot of insights into queries the server handled, it can’t help us to see which queries are running now.
Problem Statement
Real-time access to queries that are running right now can be extremely helpful in case of pileups if the optimizer gets crazy, a bad query id is deployed, or some unexpected locking situation takes place. The usual result is that many queries of the same kind pile up… and if you’re not lucky, they may not complete for many minutes or even hours, all this time invisible in PMM.
Proposed Solution
In addition to Query History, what Query Analytics really provides now is access to “Live Queries”. This basically gathers currently-running queries from all the nodes that a user currently observes (could be one node or could be a hundred), where queries can be grouped and sliced in a way similar to how Query Analytics works.
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For example, for a given a QueryId (Query Pattern), we can see how many instances of such a query are running right now, what the maximum and average execution time is so far, what database hosts and what databases it is active for, what client IPs and users this query are coming from, etc.
Some other Query Analytics features such as EXPLAIN for a query, information about involved tables, etc., also remain relevant for running queries too.
Also, working with current events and not just history means we can do more than just observe them. I could imagine killing some particular query instance or even all queries which match a particular pattern, which would be handy too.
What do you think? Would having such a “Global Processlist” feature in Percona Monitoring and Management be helpful for you? Anything else we should consider? Let me know in the comments!