On Mon, Sep 5, 2016 at 6:27 PM, Simon Riggs <si...@2ndquadrant.com> wrote: > On 4 August 2016 at 05:57, Masahiko Sawada <sawada.m...@gmail.com> wrote: > >> While reviewing freeze map code, Andres pointed out[1] that >> lazy_scan_heap could accesses visibility map twice and its logic is >> seems a bit tricky. >> As discussed before, it's not nice especially when large relation is >> entirely frozen. >> >> I posted the patch for that before but since this is an optimization, >> not bug fix, I'd like to propose it again. >> Please give me feedback. >> >> [1] >> https://www.postgresql.org/message-id/20160505000840.epatoq6d2e556446%40alap3.anarazel.de > > If we have a freeze map now, surely tables will no longer be entirely frozen?
Well, if table is completely frozen, freezing for all pages will be skipped. > What performance difference does this make, in a realistic use case? I have yet to measure performance effect but it would be effect for very large frozen table. > How would we test this to check it is exactly correct? One possible idea is that we emit the number of skipped page according visibility map as a vacuum verbose message, and check it. Regards, -- Masahiko Sawada NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
