Am 06.04.22 um 17:22 schrieb Robert Haas: > On Tue, Apr 5, 2022 at 10:34 PM Andres Freund <and...@anarazel.de> wrote: >>> Anyway, my (undisputed up to now!) understanding still is that only >>> backends _looking_ at these stats (so, e.g., accessing the pg_stat_toast >>> view) actually read the data. So, the 10-15% more space used for pg_stat >>> only affect the stats collector and _some few_ backends. >> >> It's not so simple. That stats collector constantly writes these stats out to >> disk. And disk bandwidth / space is of course a shared resource. > > Yeah, and just to make it clear, this really becomes an issue if you > have hundreds of thousands or even millions of tables. It's a lot of > extra data to be writing, and in some cases we're rewriting it all, > like, once per second.
Fair enough. At that point, a lot of things become unexpectedly painful. How many % of the installed base may that be though? I'm far from done reading the patch and mail thread Andres mentioned, but I think the general idea is to move the stats to shared memory, so that reading (and thus, persisting) pg_stats is required far less often, right? > Now if we're only incurring that overhead when this feature is > enabled, then in fairness that problem is a lot less of an issue, > especially if this is also disabled by default. People who want the > data can get it and pay the cost, and others aren't much impacted. That's the idea, yes. I reckon folks with millions of tables will scan through the docs (and postgresql.conf) very thoroughly anyway. Hence the note there. > However, experience has taught me that a lot of skepticism is > warranted when it comes to claims about how cheap extensions to the > statistics system will be. Again, fair enough! Maybe we first need statistics about statistics collection and handling? ;-) Best, -- Gunnar "Nick" Bluth Eimermacherweg 106 D-48159 Münster Mobil +49 172 8853339 Email: gunnar.bl...@pro-open.de __________________________________________________________________________ "Ceterum censeo SystemD esse delendam" - Cato