On 12 August 2016 at 18:54, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
>> On 12 August 2016 at 16:23, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> I think "global" might have implications we don't want. How about
>>> adding ", based on a system-generated seed"?
>
>> What I was trying to express was that
>
>> SELECT setseed(dp);
>> SELECT * FROM foo TABLESAMPLE ...;
>> SELECT * FROM foo TABLESAMPLE ...;
>> SELECT * FROM foo TABLESAMPLE ...;
>
>> would yield a repeatable set of samples, similarly repeatable but not
>> same samples as
>
>> SELECT * FROM foo TABLESAMPLE ... REPEATABLE;
>> SELECT * FROM foo TABLESAMPLE ... REPEATABLE;
>> SELECT * FROM foo TABLESAMPLE ... REPEATABLE;
>
> But that's *wrong*. Not all tablesample methods make any such guarantee.
> In fact, neither of our contrib methods do. Only if you use REPEATABLE
> (and the method allows it) is there any promise at all about repeatability.
OK, fair enough. I'll just use your wording then. Thanks.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
