[CALCITE-2077] Druid adapter: Use "scan" query rather than "select" query

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.16.0
• Component/s: druid-adapter
• Assignee: Nishant Bangarwa
• Reporter: Nishant Bangarwa
• Created: 03/Dec/17 07:43
• Updated: 27/Feb/24 22:23
• Resolved: 21/Dec/17 20:27

Description

The biggest difference between select query and scan query is that, scan query doesn't retain all rows in memory before rows can be returned to client.
Select query on very large segments will cause memory pressure on druid historicals if too many rows required by select query whereas Scan query doesn't have this issue.
Scan query can also return all rows without issuing another pagination query, which is extremely useful when query against historical or realtime node directly.

Issue Links

• is blocked by: CALCITE-2076 Upgrade to Druid 0.11.0
• relates to: HIVE-17627 Use druid scan query instead of the select query.