[HIVE-3302] Race condition in query plan for merging at the end of a query

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.10.0
• Fix Version/s: 0.10.0
• Component/s: Query Processor
• Hadoop Flags: Reviewed
• Assignee: Kevin Wilfong
• Reporter: Kevin Wilfong
• Created: 26/Jul/12 00:47
• Updated: 10/Jan/13 19:53
• Resolved: 04/Aug/12 17:08

Description

In the query plan that's used to merge files at the end of a query, the dependency tree looks something like:
MoveTask(1)
/ \
...ConditionalTask MoveTask(2)...
\ /
MergeTask

Here MoveTask(1) moves the partition data to a temporary location, and MoveTask(2) moves it to the final location.

However if there are dynamic partitions generated and some of these partitions are merged and others are moved, the dependency tree is changed at runtime to:
...ConditionalTask MoveTask(2)...
\ /
MergeTask
\
MoveTask(1)

This produces a race condition between the two MoveTasks where if MoveTask(2) runs before MoveTask(1) the partitions moved by MoveTask(1) will get moved to an intermediate location and never moved to the final location. In this case those partitions are quietly lost.