[HACKERS] Tuple-routing for certain partitioned tables not working as expected

Hi,

I noticed that tuple-routing for partitioned tables that contain 
non-writable foreign partitions doesn't work as expected.  Here is an 
example:

postgres=# create extension file_fdw;
postgres=# create server file_server foreign data wrapper file_fdw;
postgres=# create user mapping for CURRENT_USER server file_server;
postgres=# create table p (a int) partition by list (a);
postgres=# create foreign table t1 partition of p for values in (1) 
server file_server options (format 'csv', filename '/path/to/file', 
delimiter ',');
postgres=# create table t2 partition of p for values in (2);
postgres=# insert into p values (1);
ERROR:  cannot insert into foreign table "t1"

Looks good, but:

postgres=# insert into p values (2);
ERROR:  cannot insert into foreign table "t1"

The insert should work but doesn't.  (It also seems odd to me that the 
error message points to t1, not t2.)  The reason for that is 
CheckValidResultRel in ExecSetupPartitionTupleRouting aborts any insert 
into a partitioned table in the case where the partitioned table 
contains at least one foreign partition into which the FDW can't insert. 
  I don't think that that is intentional behavior, so I'd like to 
propose to fix that by skipping CheckValidResultRel for foreign 
partitions because we can abort an insert into a foreign partition after 
ExecFindPartition in ExecInsert, by checking to see if 
resultRelInfo->ri_FdwRoutine is not NULL.  Attached is a proposed patch 
for that.  Since COPY FROM has the same issue, I added regression tests 
for COPY FROM as well as INSERT to file_fdw.

Best regards,
Etsuro Fujita

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