[ASTERIXDB-2700] Fix invalid plan caused by order by operator in a subquery

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.9.4
• Fix Version/s: 0.9.5
• Component/s: *DB - AsterixDB, RT - Runtime
• Assignee: Ali Alsuliman
• Reporter: Ali Alsuliman
• Created: 18/Feb/20 09:19
• Updated: 06/Nov/20 17:00
• Resolved: 06/Nov/20 17:00

Description

The below query produces an invalid plan where two connectors are connected to each other. This happens when the optimizer optimizes the order-by operator by replacing it with a local order-by operator + sort-merge connector. If the parent operator of the original order-by operator introduces a connector, the plan ends up having two connectors. Here is an example query where there is an index on "user_since" and index on "author_id":

SET `compiler.sort.parallel` "false";
 
FROM (SELECT VALUE u FROM GleambookUsersCompositeRandom u WHERE u.user_since >= '2008-07-22T00:00:00' ORDER BY u.id) AS user, GleambookMessagesCompositeRandom AS msg
WHERE msg.author_id /*+ indexnl */ = user.id
SELECT user.name AS uname, msg.message AS message;