On Thu, Apr 11, 2019 at 12:49 PM Andres Freund <and...@anarazel.de> wrote: > > @@ -179,6 +184,12 @@ typedef struct TableAmRoutine > > * > > * if temp_snap is true, the snapshot will need to be deallocated at > > * scan_end. > > + * > > + * HEIKKI: table_scan_update_snapshot() changes the snapshot. That's > > + * a bit surprising for the AM, no? Can it be called when a scan is > > + * already in progress? > > Yea, it can be called when the scan is in-progress. I think we probably > should just fix calling code to not need that - it's imo weird that > nodeBitmapHeapscan.c doesn't just delay starting the scan till it has > the snapshot. This isn't new code, but it's now going to be exposed to > more AMs, so I think there's a good argument to fix it now. > > Robert: You committed that addition, in > > commit f35742ccb7aa53ee3ed8416bbb378b0c3eeb6bb9 > Author: Robert Haas <rh...@postgresql.org> > Date: 2017-03-08 12:05:43 -0500 > > Support parallel bitmap heap scans. > > do you remember why that's done?
I don't think there was any brilliant idea behind it. Delaying the scan start until it has the snapshot seems like a good idea. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
