[HIVE-7277] how to decide reduce numbers according to the input size of reduce stage rather than the input size of map stage?

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Unassigned
• Reporter: WangMeng
• Created: 24/Jun/14 05:23
• Updated: 21/Oct/22 07:20

Description

As we know ,now hive decide the reduce numbers just by the " Input size of map/ hive.exec.reducers.bytes.per.reducer(default 1G ).....

But ,I think the out put size of map stage may have a big difference from the original input size , so I think this strategy to decide reduce-numbers may be improper....

So is there any feature which can decide the reduce number just according to the out put of the map stage.? thanks .

As I know , actually ,the reduce stage will begin just after some map tasks have finished rather than until the whole map stage have finished , so I think it is improper too decide reduce numbers when the whole map stage have finished.

As someone point ,We can just according to the out put size of the earliest map tasks which have finished to estimate the whole reduce numbers......However, in fact ,now Hive has used filter push down(where) ,which may resulting a big difference from each map task .

So， this estimation is improper.

thanks .

Issue Links

• is related to: HIVE-7158 Use Tez auto-parallelism in Hive
• relates to: HIVE-17004 Calculating Number Of Reducers Looks At All Files