[HADOOP-5589] TupleWritable: Lift implicit limit on the number of values that can be stored

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.19.1
• Fix Version/s: 0.21.0
• Hadoop Flags: Reviewed
• Assignee: Jingkei Ly
• Reporter: Jingkei Ly
• Created: 27/Mar/09 12:15
• Updated: 24/Aug/10 20:36
• Resolved: 23/Apr/09 22:10

Description

TupleWritable uses an instance field of the primitive type, long, which I presume is so that it can quickly determine if a position has been written to in its array of Writables (by using bit-shifting operations on the long field). The problem with this is that it implies that there is a maximum limit of 64 values you can store in a TupleWritable.

An example of a use-case where I think this would be a problem is if you had two MR jobs with over 64 reduces tasks and you wanted to join the outputs with CompositeInputFormat - this will probably cause unexpected results in the current scheme.

At the very least, the 64-value limit should be documented in TupleWritable.