From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, "Patrik VV(dot)" <paddor(at)gmail(dot)com>, pgsql-docs(at)postgresql(dot)org |
Subject: | Re: Wording in TABLESAMPLE documentation |
Date: | 2016-08-12 17:59:16 |
Message-ID: | CANP8+jJs5_KEBsbAzxDgGLG99MjoJ05G4FiAWFbn6peNgnQGBw@mail.gmail.com |
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Lists: | pgsql-docs |
On 12 August 2016 at 18:54, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
>> On 12 August 2016 at 16:23, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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
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