On Mon, Apr 18, 2022 at 8:04 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Thu, Apr 14, 2022 at 9:09 AM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > On Thu, Apr 14, 2022 at 8:32 AM Masahiko Sawada <sawada.m...@gmail.com> > > wrote: > > > > > > > > The other part of the puzzle is the below check in the code: > > > > /* > > > > * If we reached the sync worker limit per subscription, just exit > > > > * silently as we might get here because of an otherwise harmless race > > > > * condition. > > > > */ > > > > if (nsyncworkers >= max_sync_workers_per_subscription) > > > > > > > > It is not clear to me why this check is there, if this wouldn't be > > > > there, the user would have got either a WARNING to increase the > > > > max_logical_replication_workers or the apply worker would have been > > > > restarted. Do you have any idea about this? > > > > > > Yeah, I'm also puzzled with this check. It seems that this function > > > doesn't work well when the apply worker is not running and some > > > tablesync workers are running. I initially thought that the apply > > > worker calls to this function as many as tables that needs to be > > > synced, but it checks the max_sync_workers_per_subscription limit > > > before calling to logicalrep_worker_launch(). So I'm not really sure > > > we need this check. > > > > > > > I just hope that the original author Petr J. responds to this point. I > > have added him to this email. This will help us to find the best > > solution for this problem. > > > > I did some more investigation for this code. It is added by commit [1] > and the patch that led to this commit is first time posted on -hackers > in email [2]. Now, neither the commit message nor the patch (comments) > gives much idea as to why this part of code is added but I think there > is some hint in the email [2]. In particular, read the paragraph in > the email [2] that has the lines: ".... and limiting sync workers per > subscription theoretically wasn't either (although I don't think it > could happen in practice).". > > It seems that this check has been added to theoretically limit the > sync workers even though that can't happen because apply worker > ensures that before trying to launch the sync worker. Does this theory > make sense to me? If so, I think we can change the check as: "if > (OidIsValid(relid) && nsyncworkers >= > max_sync_workers_per_subscription)" in launcher.c. This will serve the > purpose of the original code and will solve the issue being discussed > here. I think we can even backpatch this. What do you think?
+1. I also think it's a bug so back-patching makes sense to me. Regards, -- Masahiko Sawada EDB: https://www.enterprisedb.com/
