[New Feature] yb_active_session_history (ash): Asking to include PID

[pdvmoto]

Description

Asking to include PID in yb_active_session_history. This field is already present in pg_stat_activity, which seems to contain similar data. the current ysql_session_id is just a local-counter, and is not much use "externally", wheras the linux-PID will allow linkup to an actual process.

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[hbhanawat]

@pdvmoto Thanks for submitting the issue. Can you elaborate on the use case when PID will help and ysql_session_id will not? Since the PID is not available for sessions that have ended, I am not sure how to correlate that.

[FranckPachot]

I can add some cases where PID may be helpful:

• OOM killer killed a process. It is visible in the trace. Then, it can be helpful to know what this process was doing before
• a long query is running. It is visible in pg_stat_activity (with its PID) and looking at ASH may help understand (queryid is not always set and not unique)
• OS reports high CPU usage in TOP for a Postgres backend, may be good to look at ASH to understand what it is doing

[pdvmoto]

What Franck Said. The first use of PID would be for "immediate viewing" and troubleshooting. plus: I am already working to save some of the data from ahs and pg_stat_activity. This will allow after-the-fact investigation to put together the (sampled) activity of a given session (pid + startdate).

The "problem" I have with sql_session_id: it doesnt seem to link to anything (yet) ?

and I realize the limitation of "sampled" information. but ASH is a Good Start!