On Fri, Oct 23, 2015 at 6:29 AM, Simon Riggs <si...@2ndquadrant.com> wrote:
> On 21 October 2015 at 13:31, Jeff Janes <jeff.ja...@gmail.com> wrote: > > Index-only scans will visit the heap for each tuple until the first VACUUM >> is done. >> >> The first vacuum will read the entire table, but not need to write it >> anymore. And will create the _vm file. >> >> I think we really want to create _vm file as well as set PD_ALL_VISIBLE, >> but I don't know the best way to do that. Set a flag somewhere and then >> create it in bulk at the end of the transaction? Set it bit by bit as the >> pages are extended and initialized? >> > > Easy enough to do it at the end of the COPY FREEZE in one step. > Here, we might want to consider that setting bit in visibility map will generate WAL log whereas Copy Freeze otherwise skip WAL when wal_level is less than archive. This can lead to extra disk writes which can slow down Copy Freeze, but OTOH that might be acceptable. With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
