On 2018-05-11 14:59:04 -0400, Bruce Momjian wrote: > On Fri, May 11, 2018 at 11:50:51AM -0700, Andres Freund wrote: > > On 2018-05-11 14:44:06 -0400, Bruce Momjian wrote: > > > On Fri, May 11, 2018 at 07:49:50PM +0300, Teodor Sigaev wrote: > > > > > > > > > > > > Bruce Momjian wrote: > > > > >I have committed the first draft of the Postgres 11 release notes. I > > > > >will add more markup soon. You can view the most current version here: > > > > > > > > > > http://momjian.us/pgsql_docs/release-11.html > > > > > > > > > >I expect a torrent of feedback. ;-) > > > > Hi! > > > > > > > > Seems, you miss: > > > > 857f9c36cda520030381bd8c2af20adf0ce0e1d4 Skip full index scan during > > > > cleanup > > > > of B-tree indexes when possible > > > > > > I read that and thought it was too details to be in the release notes. > > > It is not that it is unimportant, but it is hard to see how people would > > > notice the difference or change their behavior based on this change. > > > > It's a *huge* performance problem in larger installations > > currently. When you have a multi-TB relation and correspondingly large > > relation, the VM allows to make the heap cleanups cheap, but then the > > index scan takes just about forever. I know at least one large PG user > > that moved off postgres because of it. This won't solve all of those > > concerns, but it definitely is crucial to know for such users. > > > > People would notice by vacuums of large relations not taking forever > > anymore. And the behaviour change would be to a) upgrade b) tune the > > associated reloption/GUC. > > OK, so what is the text that people will understand? This? > > Prevent manual VACUUMs on append-only tables from performing > needless index scans
I don't think the table being 'append-only' is necessary? Nor does it have to be a manual vacuum. And 'needless index scan' sounds less than it is/was, namely a full scan of the index. Perhaps something like: Allow vacuum to skip doing a full scan of btree indexes after VACUUM, if not necessary. or something like that? > You can see why I was hesitant to include it, based on this text, but I > am happy to add it. I can't. Even if the above were accurate it'd be relevant information. Greetings, Andres Freund
