Heikki Linnakangas wrote: > On 01.12.2010 03:35, Bruce Momjian wrote: > > Heikki Linnakangas wrote: > >> Let's recap what happens when a VM bit is set: You set the > >> PD_ALL_VISIBLE flag on the heap page (assuming it's not set already, it > >> usually isn't), and then set the bit in the VM while keeping the heap > >> page locked. > > > > What if we set PD_ALL_VISIBLE on the heap page, wait for a checkpoint to > > happen so the heap page is guaranteed to be on disk, then on next read, > > if PD_ALL_VISIBLE is set and the VM all-visible bit is not set, set the > > VM bit. > > Hmm, you'd somehow have to know if a checkpoint has happened since the > flag was set. And it might be a long wait, which makes it less
Well, doesn't the page LSN tell you that already? > attractive for index-only scans. My assumption is that this page will remain read-only for a while, so I don't see the big downside in a delay of max 5-10 minutes. For sites where pages go frequently in and out of read-only status, I don't think index-only scans are every going to be a big win. Long-running queries alone are going to delay how quickly we can set PD_ALL_VISIBLE, so I don't see an additional 5-10 minutes as a big problem. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers