Re: Indexes on partitioned tables and foreign partitions

On 2018/05/10 10:02, Michael Paquier wrote:
> Something
> that I find confusing on HEAD though is that DefineIndex calls itself
> around line 1006 and cascades through each children but there is no
> context about the error.
> 
> For example if I have this partition layer:
> CREATE TABLE measurement (
>      logdate         date not null,
>      peaktemp        int,
>      unitsales       int
> ) PARTITION BY RANGE (logdate);
> CREATE FOREIGN TABLE measurement_y2016m07
>     PARTITION OF measurement FOR VALUES FROM ('2016-07-01') TO
>     ('2016-08-01')
>     SERVER postgres_server;
> 
> Then by creating an index on the parent I get that:
> =# create index measurement_idx on measurement (peaktemp);
> ERROR:  42809: cannot create index on foreign table "measurement_y2016m07"
> LOCATION:  DefineIndex, indexcmds.c:442
> 
> This may be confusing for the user as the DDL does not complain directly
> about the relation worked on.  Perhaps we could add an error context?
> We surely don't want multiple contexts either when working on long
> chains, but we could build a chained list of relation names in the error
> message.

How about we error out even *before* calling DefineIndex for the 1st time?
 I see that ProcessUtilitySlow() gets a list of all partitions when
locking them for index creation before calling DefineIndex.  Maybe, just
go through the list and error out if one of them is a partition that we
don't support creating an index on?

For example, with the attached patch doing the above, I get:

create table p (a int) partition by range (a);
create table p1 partition of p for values from (minvalue) to (1);
create foreign table p2 partition of p for values from (1) to (maxvalue)
server loopback options (table_name 'p2base');
create index on p (a);
ERROR:  cannot create index on partitioned table containing foreign partitions

Thanks,
Amit