On Fri, Jan 13, 2023 at 11:50 AM Peter Smith <smithpb2...@gmail.com> wrote: > > Here are some review comments for patch v79-0002. >
So, this is about the latest v84-0001-Stop-extra-worker-if-GUC-was-changed. > ====== > > General > > 1. > > I saw that earlier in this thread Hou-san [1] and Amit [2] also seemed > to say there is not much point for this patch. > > So I wanted to +1 that same opinion. > > I feel this patch just adds more complexity for almost no gain: > - reducing the 'max_apply_workers_per_suibscription' seems not very > common in the first place. > - even when the GUC is reduced, at that point in time all the workers > might be in use so there may be nothing that can be immediately done. > - IIUC the excess workers (for a reduced GUC) are going to get freed > naturally anyway over time as more transactions are completed so the > pool size will reduce accordingly. > I am still not sure if it is worth pursuing this patch because of the above reasons. I don't think it would be difficult to add this even at a later point in time if we really see a use case for this. Sawada-San, IIRC, you raised this point. What do you think? The other point I am wondering is whether we can have a different way to test partial serialization apart from introducing another developer GUC (stream_serialize_threshold). One possibility could be that we can have a subscription option (parallel_send_timeout or something like that) with some default value (current_timeout used in the patch) which will be used only when streaming = parallel. Users may want to wait for more time before serialization starts depending on the workload (say when resource usage is high on a subscriber-side machine, or there are concurrent long-running transactions that can block parallel apply for a bit longer time). I know with this as well it may not be straightforward to test the functionality because we can't be sure how many changes would be required for a timeout to occur. This is just for brainstorming other options to test the partial serialization functionality. Thoughts? -- With Regards, Amit Kapila.
