Add basic read-only transaction tests

src/test/regress/expected/multi_basic_queries.out

@@ -22,6 +22,16 @@ SELECT avg(l_extendedprice) FROM lineitem;
  38141.835375000000
 (1 row)
 
+-- Verify that we can do queries in read-only mode
+BEGIN;
+SET TRANSACTION READ ONLY;
+SELECT count(*) FROM lineitem;
+ count 
+-------
+ 12000
+(1 row)
+
+COMMIT;
 -- Verify temp tables which are used for final result aggregation don't persist.
 SELECT count(*) FROM pg_class WHERE relname LIKE 'pg_merge_job_%' AND relkind = 'r';
  count 

src/test/regress/expected/multi_router_planner.out

@@ -2023,6 +2023,26 @@ DEBUG:  Plan is router executable
  41 |         1 | aznavour     |      11814
 (5 rows)
 
+END;
+-- queries inside read-only transactions can be router plannable
+BEGIN;
+SET TRANSACTION READ ONLY;
+SELECT *
+	FROM articles_hash
+	WHERE author_id = 1
+	ORDER BY id;
+DEBUG:  predicate pruning for shardId 840001
+DEBUG:  Creating router plan
+DEBUG:  Plan is router executable
+ id | author_id |    title     | word_count 
+----+-----------+--------------+------------
+  1 |         1 | arsenous     |       9572
+ 11 |         1 | alamo        |       1347
+ 21 |         1 | arcading     |       5890
+ 31 |         1 | athwartships |       7271
+ 41 |         1 | aznavour     |      11814
+(5 rows)
+
 END;
 -- cursor queries are router plannable
 BEGIN;

src/test/regress/expected/multi_utilities.out

@@ -19,6 +19,12 @@ SELECT master_create_worker_shards('sharded_table', 2, 1);
 COPY sharded_table TO STDOUT;
 COPY (SELECT COUNT(*) FROM sharded_table) TO STDOUT;
 0
+BEGIN;
+SET TRANSACTION READ ONLY;
+COPY sharded_table TO STDOUT;
+COPY (SELECT COUNT(*) FROM sharded_table) TO STDOUT;
+0
+COMMIT;
 -- cursors may not involve distributed tables
 DECLARE all_sharded_rows CURSOR FOR SELECT * FROM sharded_table;
 ERROR:  DECLARE CURSOR can only be used in transaction blocks

src/test/regress/sql/multi_basic_queries.sql

@@ -15,5 +15,11 @@ SELECT sum(l_extendedprice) FROM lineitem;
 
 SELECT avg(l_extendedprice) FROM lineitem;
 
+-- Verify that we can do queries in read-only mode
+BEGIN;
+SET TRANSACTION READ ONLY;
+SELECT count(*) FROM lineitem;
+COMMIT;
+
 -- Verify temp tables which are used for final result aggregation don't persist.
 SELECT count(*) FROM pg_class WHERE relname LIKE 'pg_merge_job_%' AND relkind = 'r';

src/test/regress/sql/multi_router_planner.sql

@@ -906,6 +906,15 @@ SELECT *
 	ORDER BY id;
 END;
 
+-- queries inside read-only transactions can be router plannable
+BEGIN;
+SET TRANSACTION READ ONLY;
+SELECT *
+	FROM articles_hash
+	WHERE author_id = 1
+	ORDER BY id;
+END;
+
 -- cursor queries are router plannable
 BEGIN;
 DECLARE test_cursor CURSOR FOR 

src/test/regress/sql/multi_utilities.sql

@@ -14,6 +14,12 @@ SELECT master_create_worker_shards('sharded_table', 2, 1);
 COPY sharded_table TO STDOUT;
 COPY (SELECT COUNT(*) FROM sharded_table) TO STDOUT;
 
+BEGIN;
+SET TRANSACTION READ ONLY;
+COPY sharded_table TO STDOUT;
+COPY (SELECT COUNT(*) FROM sharded_table) TO STDOUT;
+COMMIT;
+
 -- cursors may not involve distributed tables
 DECLARE all_sharded_rows CURSOR FOR SELECT * FROM sharded_table;