Re: getting rid of SnapshotNow

Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Jul 23, 2013 at 12:28 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> As far as get_actual_variable_range() is concerned, an MVCC snapshot
>> would probably be the thing to use anyway;

> That surprises me, though.  I really thought the point was to cost the
> index scan, and surely that will be slowed down even by entries we
> can't see.

No, the usage (or the main usage anyway) is for selectivity estimation,
ie how many rows will the query fetch.
        regards, tom lane