On 03/17/2018 05:43 AM, Arthur Zakirov wrote: > Hello Tomas, > > Arthur, what are your plans with this patch in the current CF? > > > I think dsm-based approach is in good shape already and works nice. > I've planned only to improve the documentation a little. Also it seems I > should change 0004 part, I found that extension upgrade scripts may be > made in wrong way. > In my opinion RELOAD and UNLOAD commands can be made in next commitfest > (2018-09). > Did you look it? Have you arguments about how shared memory allocation > and releasing functions are made? > > > > It does not seem to be moving towards RFC very much, and reworking the > patch to use mmap() seems like a quite significant change late in the > CF. Which means it's likely to cause the patch get get bumped to the > next CF (2018-09). > > > Agree. I have a draft version for mmap-based approach which works in > platforms with mmap. In Windows it is necessary to use another API > (CreateFileMapping, etc). But this approach requires more work on > handling processed dictionary files (how name them, when remove). > > > > FWIW I am not quite sure if the mmap() approach is better than what was > implemented by the patch. I'm not sure how exactly will it behave under > memory pressure (AFAIK it goes through page cache, which means random > parts of dictionaries might get evicted) or how well is it supported on > various platforms (say, Windows). > > > Yes, as I wrote mmap-based approach requires more work. The only > benefit I see is that you don't need to process a dictionary after > server restart. I'd vote for dsm-based approach. >
I do agree with that. We have a working well-understood dsm-based solution, addressing the goals initially explained in this thread. I don't see a reason to stall this patch based on a mere assumption that the mmap-based approach might be magically better in some unknown aspects. It might be, but we may as well leave that as a future work. I wonder how much of this patch would be affected by the switch from dsm to mmap? I guess the memory limit would get mostly irrelevant (mmap would rely on the OS to page the memory in/out depending on memory pressure), and so would the UNLOAD/RELOAD commands (because each backend would do it's own mmap). In any case, I suggest to polish the dsm-based patch, and see if we can get that one into PG11. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
