On Fri, Oct 4, 2019 at 2:31 PM Amit Kapila <amit.kapila16@gmail.com> wrote: >> > > Do we really need to log all those messages? The other places where we launch parallel workers doesn't seem to be using such messages. Why do you think it is important to log the messages here when other cases don't use it?
Well I would rather think that parallel create index doesn't log enough messages. Parallel maintenance operation is invoked manually by user. I can imagine that DBA wants to cancel and try the operation again later if enough workers are not launched. But there is not a convenient way to confirm how many parallel workers planned and actually launched. We need to see ps command or pg_stat_activity. That's why I think that log message would be helpful for users.
Hmm, what is a guarantee at a later time the user will get the required number of workers? I think if the user decides to vacuum, then she would want it to start sooner. Also, to cancel the vacuum, for this reason, the user needs to monitor logs which don't seem to be an easy thing considering this information will be logged at DEBUG2 level. I think it is better to add in docs that we don't guarantee that the number of workers the user has asked or expected to use for a parallel vacuum will be available during execution. Even if there is a compelling reason (which I don't see) to log this information, I think we shouldn't use more than one message to log (like there is no need for a separate message for cleanup and vacuuming) this information.