On Thu, Dec 21, 2017 at 6:26 PM, Robert Haas <robertmh...@gmail.com> wrote: > On Thu, Dec 21, 2017 at 6:46 AM, Amit Kapila <amit.kapil...@gmail.com> wrote: >> What if we don't allow to reuse such slots till the backend/session >> that has registered it performs unregister? Currently, we don't seem >> to have an API corresponding to Register*BackgroundWorker() which can >> be used to unregister, but maybe we can provide such an API. > > Well, then we could have slots pinned down for a long time, if the > backend never gets around to calling unregister. Furthermore, that's > absolutely not back-patchable, because we can't put a requirement like > that on code running in the back branches. Also, what if the code > path that would have done the unregister eventually errors out? We'd > need TRY/CATCH blocks everywhere that registers the worker. In short, > this seems terrible for multiple reasons. > >>> Furthermore, it doesn't help in the case where the worker starts and >>> immediately exits without attaching to the DSM. >> >> Yeah, but can't we detect that case? After the worker exits, we can >> know its exit status as is passed to CleanupBackgroundWorker, we can >> use that to mark the worker state as BGWH_ERROR_STOPPED (or something >> like BGWH_IMMEDIATE_STOPPED). >> >> I think above way sounds invasive, but it seems to me that it can be >> used by other users of background workers as well. > > The exit status doesn't tell us whether the worker attached to the DSM. > > I'm relatively puzzled as to why you're rejecting a relatively > low-impact way of handling a corner case that was missed in the > original design in favor of major architectural changes. >
I am not against using the way specific to parallel context layer as described by you above. However, I was trying to see if there is some general purpose solution as the low-impact way is not very straightforward. I think you can go ahead with the way you have described to fix the hole I was pointing to and I can review it or I can also give it a try if you want to. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
