[DRILL-2723] Inaccurate row count estimate for text files results in BroadcastExchange

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.0.0
• Component/s: Query Planning & Optimization
• Assignee: Jacques Nadeau
• Reporter: Steven Phillips
• Created: 08/Apr/15 21:20
• Updated: 10/May/15 20:26
• Resolved: 10/May/15 20:26

Description

The current method for estimating row count in text files is to divide the size of the file in bytes by 1024. This row count estimate is used by optimizer to decide if BroadcastExchange should be used.

This results in massive memory consumption when using BroadCast exchange on a large table.

We need a better way of estimating row count, or use a different metric when deciding to use BroadcastExchange.