> Indeed. > It might have already been discussed but other than using a new shmem > hash for parallel vacuum, I wonder if we can allow workers to change > the leader’s progress information. It would break the assumption that > the backend status entry is modified by its own backend, though. But > it might help for progress updates of other parallel operations too. > This essentially does the same thing as what the current patch does > but it doesn't require a new shmem hash.
I experimented with this idea, but it did not work. The idea would have been to create a pgstat_progress_update function that takes the leader pid, however infrastructure does not exist to allow one backend to manipulate another backends backend status array. pgstat_fetch_stat_beentry returns a local copy only. > Another idea I come up with is that the parallel vacuum leader checks > PVIndStats.status and updates how many indexes are processed to its > progress information. The leader can check it and update the progress > information before and after index vacuuming. And possibly we can add > a callback to the main loop of index AM's bulkdelete and vacuumcleanup > so that the leader can periodically make it up-to-date. > Regards, The PVIndStats idea is also one I experimented with but it did not work. The reason being the backend checking the progress needs to do a shm_toc_lookup to access the data, but they are not prepared to do so. I have not considered the callback in the index AM's bulkdelete and vacuumcleanup, but I can imagine this is not possible since a leader could be busy vacuuming rather than updating counters, but I may be misunderstanding the suggestion. -- Sami Imseih Amazon Web Services
