Yuta Morisawa created FLINK-8532:
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Summary: RebalancePartitioner should use Random value for its
first partition
Key: FLINK-8532
URL: https://issues.apache.org/jira/browse/FLINK-8532
Project: Flink
Issue Type: Improvement
Components: DataStream API
Reporter: Yuta Morisawa
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.
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