Hi, On 2021-03-11 19:22:57 -0800, Andres Freund wrote: > I started changing the patch to address my complaints. I'll try to do > it as an incremental patch ontop of your 0004, but it might become too > unwieldy. Not planning to touch other patches for now (and would be > happy if the first few were committed). I do think we'll have to > split 0004 a bit - it's just too large to commit as is, I think.
Far from being done (and the individual commits is just me working, not something that is intended to survive), but I thought it might be helpful to post my WIP git tree: https://github.com/anarazel/postgres/commits/shmstat I do think that the removal of the the "attach" logic, as well as the more explicit naming differentiating between the three different hash tables is a pretty clear improvement. It's way too easy to get turned around otherwise. I suspect to make all of this workable we'll have to add a few preliminary cleanup patches. I'm currently thinking: 1) There's a bunch of functions in places that don't make sense. /* ------------------------------------------------------------ * Local support functions follow * ------------------------------------------------------------ */ [internal stuff] ... void pgstat_send_archiver(const char *xlog, bool failed) ... void pgstat_send_bgwriter(void) ... void pgstat_report_wal(void) ... bool pgstat_send_wal(bool force) ... [internal stuff] ... void pgstat_count_slru_page_zeroed(int slru_idx) ... I think it'd make sense to separately clean that up. 2) src/backend/postmaster/pgstat.c currently contains at least two, effectively independent, subsystems. Arguably more: a) cumulative stats collection infrastructure: sending data to the persistent stats file, and reading from it. b) "content aware" cumulative statistics function c) "current" activity infrastructure, around PgBackendStatus (which basically boils down to pg_stat_activity et al.) d) wait events e) command progress stuff They don't actually have much to do with each other, except being related to stats. Even without the shared memory stats, having these be in one file makes pretty much no sense. Having them all under one common pgstat_* prefix is endlessly confusing too. I think before making things differently complicated with this patch, we need to clean this up, unfortunately. I think we should initially have - src/backend/postmaster/pgstat.c, for a), b) above - src/backend/utils/activity/backend_status.c for c) - src/backend/utils/activity/wait_events.c for d) - src/backend/utils/activity/progress.c for e) Not at all sure about the names, but something roughly like this would im make sense. The next thing to note is that after this whole patchseries, having the remaining functionality in src/backend/postmaster/pgstat.c doesn't make sense. The things in postmaster/ are related to postmaster sub-processes, not random pieces of backend infrastructure. Therefore I am thinking that patch 0004 should be changed so it basically adds all the changed code to two new files: - src/backend/utils/activity/stats.c - for the stats keeping infrastructure (shared memory hash table, pending table, etc) - src/backend/utils/activity/stats_report.c - for pgstat_report_*, pgstat_count_*, pgstat_update_*, flush_*, i.e. everything that knows about specific kinds of stats. The reason for that split is that imo the two pieces of code are largely independent. One shouldn't need to understand the way stats are stored in any sort of detail to add a new stats field and vice versa. Horiguchi-san, is there a chance you could add a few tests (on master) that test/document the way stats are kept across "normal" restarts, and thrown away after crash restarts/immediate restarts and also thrown away graceful streaming rep shutdowns? Greetings, Andres Freund
