On Fri, Nov 6, 2015 at 2:03 PM, Kevin Grittner <kgrittn@ymail.com> wrote: > Has anyone taken a close look at what happens if the two sides of > the merge join have different implementations of the same collation > name? Is there anything we should do to defend against the > problem?
The issue of FDWs vs. collations has been thought about to some degree (see FDW_COLLATE_NONE/SAFE/UNSAFE), but I don't quite understand that stuff in detail> . >
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.
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Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company
