Re: Getting sorted data from foreign server for merge join

On 16 November 2015 at 17:47, Ashutosh Bapat <
ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
>
>
> collations arising from a foreign table's var are considered to be safer
> (FDW_COLLATE_SAFE) to push down to the foreign server , since they are
> either local default collation or are assumed to be same on foreign and
> local server as per user declaration. The onus of making that sure is on
> the user who declares particular collation for a foreign table var. As said
> upthread, different glibc implementations can cause collation ordering
> mismatch, this patch will be susceptible to the same problem as
> master/standby problem.
>
>
Yeah. It's less bad than the related problems we already have:

* Upgrading glibc can cause your indexes to no longer match your local
collations
* Different glibc versions on master and replica(s) can have the same effect

I don't see a problem with adding another way this same issue can be
expressed, since there's no sane way to fix it _properly_ without either
versioned collations in glibc or bringing collation onboard into Pg.

--
Craig Ringer http://www.2ndQuadrant.com/
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