[DRILL-7490] limit is not pushed to JDBC storage plugin

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.11.0
• Fix Version/s: 1.17.0
• Component/s: Query Planning & Optimization, Storage - JDBC
• Labels: ready-to-commit
• Assignee: Vova Vysotskyi
• Reporter: Vova Vysotskyi
• Reviewer: Arina Ielchiieva
• Created: 18/Dec/19 16:59
• Updated: 01/Dec/20 21:16
• Resolved: 22/Dec/19 11:43

Description

The limit is not pushed to JDBC storage plugin. 
The following query:

select person_id from mysql.`drill_mysql_test`.person limit 10

Returns plan:

00-00    Screen
00-01      Project(person_id=[$0])
00-02        SelectionVectorRemover
00-03          Limit(fetch=[10])
00-04            Limit(fetch=[10])
00-05              Jdbc(sql=[SELECT `person_id` FROM `drill_mysql_test`.`person` ])

This issue happens since incorrect row count is calculated for JdbcSort.
Drill enforces to use RelNode.estimateRowCount(mq) for calculating row count for all inheritants of Sort rel node (see DrillRelMdRowCount), but JdbcSort doesn't override this method and uses parent one which returns row count of input. So planner choses DrillLimitRel since it has less row count.

Issue Links

• relates to: DRILL-7771 Order by and limit transactions in RDBMS cannot be pushdown
• links to: GitHub Pull Request #1936