[SPARK-23005] Improve RDD.take on small number of partitions

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.2.1
• Fix Version/s: 2.3.0
• Component/s: Spark Core
• Assignee: Gengliang Wang
• Reporter: Gengliang Wang
• Created: 09/Jan/18 12:08
• Updated: 10/Jan/18 02:17
• Resolved: 10/Jan/18 02:17

Description

In current implementation of RDD.take, we overestimate the number of partitions we need to try by 50%:
`(1.5 * num * partsScanned / buf.size).toInt`
However, when the number is small, the result of `.toInt` is not what we want.
E.g, 2.9 will become 2, which should be 3.
Use math.Ceil fix the problem.

Issue Links

• links to: [Github] Pull Request #20200 (gengliangwang)