Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs)

On 2016/02/10 4:16, Robert Haas wrote:

On Tue, Feb 9, 2016 at 8:39 AM, Ashutosh Bapat
<ashutosh.bapat@enterprisedb.com> wrote:

Thanks Jeevan for your review and comments. PFA the patch which fixes those.

Committed with a couple more small adjustments.

Thanks for working on this, Robert, Ashutosh, and everyone involved!

I happened to notice that this code in foreign_join_ok():

    switch (jointype)
    {
        case JOIN_INNER:
            fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
                                               fpinfo_i->remote_conds);
            fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
                                               fpinfo_o->remote_conds);
            break;

        case JOIN_LEFT:
            fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
                                              fpinfo_i->remote_conds);
            fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
                                               fpinfo_o->remote_conds);
            break;

        case JOIN_RIGHT:
            fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
                                              fpinfo_o->remote_conds);
            fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
                                               fpinfo_i->remote_conds);
            break;

        case JOIN_FULL:
            fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
                                              fpinfo_i->remote_conds);
            fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
                                              fpinfo_o->remote_conds);
            break;

        default:
            /* Should not happen, we have just check this above */
            elog(ERROR, "unsupported join type %d", jointype);
    }

would break the list fpinfo_i->remote_conds in the case of INNER JOIN or FULL JOIN.  You can see the list breakage from e.g., the following queries on an Assert-enabled build:

postgres=# create extension postgres_fdw;
CREATE EXTENSION
postgres=# create server myserver foreign data wrapper postgres_fdw options (dbname 'mydatabase');
CREATE SERVER
postgres=# create user mapping for current_user server myserver;
CREATE USER MAPPING
postgres=# create foreign table foo (a int) server myserver options (table_name 'foo');
CREATE FOREIGN TABLE
postgres=# create foreign table bar (a int) server myserver options (table_name 'bar');
CREATE FOREIGN TABLE
postgres=# create foreign table baz (a int) server myserver options (table_name 'baz');
CREATE FOREIGN TABLE
postgres=# select * from foo, bar, baz where foo.a = bar.a and bar.a = baz.a and foo.a < 10 and bar.a < 10 and baz.a < 10;

Attached is a patch to avoid the breakage.

Best regards,
Etsuro Fujita