Re: index-only scans vs. Hot Standby, round two

On Fri, Apr 13, 2012 at 5:33 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> Currently, we have a problem with index-only scans in Hot Standby
> mode: the xmin horizon on the standby might lag the master, and thus
> an index-only scan might mistakenly conclude that no heap fetch is
> needed when in fact it is.  I suggested that we handle this by
> suppressing generation of index-only scan plans in Hot Standby mode,
> but Simon, Noah, and Dimitri were arguing that we should instead do
> the following, which is now on the open items list:
>
> * Make XLOG_HEAP2_VISIBLE records generate recovery snapshot conflicts
> so that IndexOnlyScans work on Hot Standby
...
<snip> very long email </snip>

Luckily its much simpler than all of that suggests. It'll take a few
hours for me to write a short reply but its Sunday today, so that will
happen later.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services