Example: LIMIT OFFSET pushdown v2

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This example shows LIMIT OFFSET pushdown between the foreign tables of the same remote HIVE/SPARK server as the remote HIVE/SPARK server:

Tables on HIVE/SPARK server:

0: jdbc:hive2://localhost:10000> describe emp;
+-----------+------------+----------+--+
| col_name  | data_type  | comment  |
+-----------+------------+----------+--+
| empno     | int        | NULL     |
| ename     | string     | NULL     |
| job       | string     | NULL     |
| mgr       | int        | NULL     |
| hiredate  | date       | NULL     |
| sal       | int        | NULL     |
| comm      | int        | NULL     |
| deptno    | int        | NULL     |
+-----------+------------+----------+--+
8 rows selected (0.747 seconds)
0: jdbc:hive2://localhost:10000> describe dept;
+-----------+------------+----------+--+
| col_name  | data_type  | comment  |
+-----------+------------+----------+--+
| deptno    | int        | NULL     |
| dname     | string     | NULL     |
| loc       | string     | NULL     |
+-----------+------------+----------+--+
3 rows selected (0.067 seconds)

Tables on Postgres server:

-- load extension first time after install
CREATE EXTENSION hdfs_fdw;

-- create server object
CREATE SERVER hdfs_server FOREIGN DATA WRAPPER hdfs_fdw OPTIONS(host 'localhost', port '10000', client_type 'spark', auth_type 'LDAP');

-- create user mapping
CREATE USER MAPPING FOR public SERVER hdfs_server OPTIONS (username 'user1', password 'pwd123');

-- create foreign table
CREATE FOREIGN TABLE emp (
    empno           INTEGER,
    ename           VARCHAR(10),
    job             VARCHAR(9),
    mgr             INTEGER,
    hiredate        DATE,
    sal             INTEGER,
    comm            INTEGER,
    deptno          INTEGER
)
SERVER hdfs_server OPTIONS (dbname 'fdw_db', table_name 'emp');

Query with LIMIT OFFSET pushdown:

-- LIMIT OFFSET
EXPLAIN (VERBOSE, COSTS OFF)
SELECT empno FROM emp e ORDER BY empno LIMIT 5 OFFSET 2;

Output

QUERY PLAN                                          
---------------------------------------------------------------------------------------------
 Foreign Scan on public.emp e
   Output: empno
   Remote SQL: SELECT  FROM . ORDER BY  ASC NULLS LAST LIMIT 2, 5
(3 rows)

SELECT empno FROM emp e ORDER BY empno LIMIT 5 OFFSET 2;
__OUTPUT__
 empno 
-------
  7521
  7566
  7654
  7698
  7782
(5 rows)