On Tue, Jul 23, 2013 at 2:24 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 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.
OK, so GetActiveSnapshot()?
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company