On Tue, Jun 8, 2010 at 5:08 PM, Simon Riggs <si...@2ndquadrant.com> wrote: >> > Why not just have a separate flag for HEAP_XMIN_FROZEN, that way we can >> > keep the xmin but also can see it is frozen? >> >> We could do that, but I think the point of this exercise is to reduce >> I/O - specifically, I/O caused by anti-wraparound vacuums - and I'm >> not clear how such a flag would help with that. > > Hmmm: You suggested a variant of this idea, so whatever reasoning was > behind your suggestion would be shared here, surely? > > Tom has been saying we cannot freeze early because we need to keep > xmins. I agree with that. This suggestion shows it is possible to freeze > a tuple AND keep its xmin. So that removes the argument that we should > freeze more aggressively (whenever we write the block) and can thus > reduce longer term I/O costs.
OK, yes, I see what you're getting at now. There are two possible ways to do freeze the tuples and keep the xmin: we can either rely on the PD_ALL_VISIBLE page-level bit (as I previously proposed) or we can additionally have a HEAP_XMIN_FROZEN bit as you propose here. I am not sure which way is better. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
