Going with ' logical_decoding_work_mem' seems a reasonable solution, but since we are mixing the functionality of developer and production GUC, there is a slight risk that customer/DBAs may end up setting it to 0 and forget about it and thus hampering system's performance. Have seen many such cases in previous org.
Adding a new developer parameter seems slightly safe, considering we already have one such category supported in postgres. It can be on the same line as that of 'force_parallel_mode'. It will be purely developer GUC, plus if we want to extend something in future to add/automate heavier test-cases or any other streaming related dev option, we can extend the same parameter w/o disturbing production's one. (see force_parallel_mode=regress for ref). thanks Shveta On Wed, Dec 21, 2022 at 11:25 AM Hayato Kuroda (Fujitsu) < kuroda.hay...@fujitsu.com> wrote: > Dear Amit, > > > The other possibility to achieve what you are saying is that we allow > > a minimum value of logical_decoding_work_mem as 0 which would mean > > stream or serialize each change depending on whether the streaming > > option is enabled. > > I understood that logical_decoding_work_mem may double as normal option as > developer option. I think yours is smarter because we can reduce # of GUCs. > > > I think we normally don't allow a minimum value > > below a certain threshold for other *_work_mem parameters (like > > maintenance_work_mem, work_mem), so we have followed the same here. > > And, I think it makes sense from the user's perspective because below > > a certain threshold it will just add overhead by either writing small > > changes to the disk or by sending those over the network. However, it > > can be quite useful for testing/debugging. So, not sure, if we should > > restrict setting logical_decoding_work_mem below a certain threshold. > > What do you think? > > You mean to say that there is a possibility that users may set a small > value without deep > considerations, right? If so, how about using the approach like > autovacuum_work_mem? > > autovacuum_work_mem has a range [-1, MAX_KIROBYTES], and -1 mean that it > follows > maintenance_work_mem. If it is set small value like 5KB, its working > memory is rounded > up to 1024KB. See check_autovacuum_work_mem(). > > Based on that, I suggest followings. Can they solve the problem what you > said? > > * If logical_decoding_work_mem is set to 0, all transactions are streamed > or serialized > on publisher. > * If logical_decoding_work_mem is set within [1, 63KB], the value is > rounded up or ERROR > is raised. > * If logical_decoding_work_mem is set greater than or equal to 64KB, the > set value > is used. > > Best Regards, > Hayato Kuroda > FUJITSU LIMITED > > Amit Kapila. >
