[IGNITE-18517] Sql. SELECT with LIMIT prefetch more data than necessary.

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: sql
• Labels: calcite2-required calcite3-required
• Epic Link: AI3 Performance
• Assignee: Unassigned
• Reporter: Evgeny Stanilovsky
• Created: 10/Jan/23 11:39
• Updated: 13/Jun/23 13:35

Description

This is just an optimization issue, not bug.
Simple distributed request like : SELECT * FROM T LIMIT N;

IgniteLimit
  IgniteExchange
    IgniteTableScan

need to request (maximum) N rows from each TableScan, but for now requested :
Outbox#flush -> source().request(waiting = IN_BUFFER_SIZE);