[FLINK-8532] RebalancePartitioner should use Random value for its first partition

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.7.0
• Component/s: API / DataStream
• Labels: pull-request-available
• Assignee: Guibo Pan
• Reporter: Yuta Morisawa
• Created: 31/Jan/18 07:40
• Updated: 06/Oct/18 23:00
• Resolved: 06/Oct/18 22:58

Description

In some conditions, RebalancePartitioner doesn't balance data correctly because it use the same value for selecting next operators.

RebalancePartitioner initializes its partition id using the same value in every threads, so it indeed balances data, but at one moment the amount of data in each operator is skew.

Particularly, when the data rate of  former operators is equal , data skew becomes severe.

 

 

Example:

Consider a simple operator chain.

-> map1 -> rebalance -> map2 ->

Each map operator(map1, map2) contains three subtasks(subtask 1, 2, 3, 4, 5, 6).

map1          map2

 st1              st4

 st2              st5

 st3              st6

 

At the beginning, every subtasks in map1 sends data to st4 in map2 because they use the same initial parition id.

Next time the map1 receive data st1,2,3 send data to st5 because they increment its partition id when they processed former data.

In my environment,  it takes twice the time to process data when I use RebalancePartitioner  as long as I use other partitioners(rescale, keyby).

 

To solve this problem, in my opinion, RebalancePartitioner should use its own operator id for the initial value.

 

Issue Links

• links to: GitHub Pull Request #6544