Le jeudi 19 décembre 2013 03:08:59, Robert Haas a écrit : > On Wed, Dec 18, 2013 at 6:07 PM, Cédric Villemain <ced...@2ndquadrant.fr> wrote: > >> When the prefetch process starts up, it services requests from the > >> queue by reading the requested blocks (or block ranges). When the > >> queue is empty, it sleeps. If it receives no requests for some period > >> of time, it unregisters itself and exits. This is sort of a souped-up > >> version of the hibernation facility we already have for some auxiliary > >> processes, in that we don't just make the process sleep for a longer > >> period of time but actually get rid of it altogether. > > > > I'm just a bit skeptical about the starting time: backend will ReadBuffer > > very soon after requesting the Prefetch... > > Yeah, absolutely. The first backend that needs a prefetch probably > isn't going to get it in time. I think that's OK though. Once the > background process is started, response times will be quicker... > although possibly still not quick enough. We'd need to benchmark this > to determine how quickly the background process can actually service > requests. Does anybody have a good self-contained test case that > showcases the benefits of prefetching?
Bitmap heap fetch, I haven't a selfcase here. I didn't CC Greg but I'm sure he has the material your asking. -- Cédric Villemain +33 (0)6 20 30 22 52 http://2ndQuadrant.fr/ PostgreSQL: Support 24x7 - Développement, Expertise et Formation
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