Simon Riggs wrote: > On 15 April 2015 at 09:10, Andres Freund <and...@anarazel.de> wrote:
> > I don't really see the downside to this suggestion. > > The suggestion makes things better than they are now but is still less > than I have proposed. > > If what you both mean is "IMHO this is an acceptable compromise", I > can accept it also, at this point in the CF. Let me see if I understand things. What we have now is: when reading a page, we also HOT-clean it. This runs HOT-cleanup a large number of times, and causes many pages to become dirty. Your patch is "when reading a page, HOT-clean it, but only 5 times in each scan". This runs HOT-cleanup at most 5 times, and causes at most 5 pages to become dirty. Robert's proposal is "when reading a page, if dirty HOT-clean it; if not dirty, also HOT-clean it but only 5 times in each scan". This runs HOT-cleanup some number of times (as many as there are dirty), and causes at most 5 pages to become dirty. Am I right in thinking that HOT-clean in a dirty page is something that runs completely within CPU cache? If so, it would be damn fast and would have benefits for future readers, for very little cost. Dirtying a page is very different; if buffer reads are common, the system is later bogged down trying to find clean pages to read uncached buffers (including the read-only scan itself, so it becomes slower.) If I have understood things correctly, then I stand behind Robert's suggestion. -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
