[PIG-1249] Safe-guards against misconfigured Pig scripts without PARALLEL keyword

• Type: Improvement
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.8.0
• Fix Version/s: 0.8.0

Release Note

In the previous versions of Pig, if the number of reducers was not specified (via PARALLEL or default_parallel), the value of 1 was used which in many cases was not a good choice and caused severe performance problems.

In Pig 0.8.0, a simple heuristic is used to come up with a better number based on the size of the input data. There are several parameters that the user can control:

pig.exec.reducers.bytes.per.reducer - define number of input bytes per reduce; default value is 1000*1000*1000 (1GB)
pig.exec.reducers.max - defines the upper bound on the number of reducers; default is 999

The formula is very simple:

#reducers = MIN (pig.exec.reducers.max, total input size (in bytes) / bytes per reducer.

This is a very simplistic formula that we would need to improve over time. Note, that the computed value takes all inputs within the script into account and applies the computed value to all the jobs within Pig script.

Note that this is not a backward compatible change and set default_parallel to restore the value to 1

• Assignee: Jeff Zhang
• Reporter: Arun Murthy
• Created: 22/Feb/10 18:20
• Updated: 19/Jan/11 09:01
• Resolved: 29/Jul/10 00:25

Description

It would be very useful for Pig to have safe-guards against naive scripts which process a lot of data without the use of PARALLEL keyword.

We've seen a fair number of instances where naive users process huge data-sets (>10TB) with badly mis-configured #reduces e.g. 1 reduce.

Issue Links

• relates to: MAPREDUCE-1521 Protection against incorrectly configured reduces