Felix Neutatz created FLINK-4175:
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Summary: Broadcast data sent increases with # slots per TM
Key: FLINK-4175
URL: https://issues.apache.org/jira/browse/FLINK-4175
Project: Flink
Issue Type: Improvement
Components: Core, TaskManager
Affects Versions: 1.0.3
Reporter: Felix Neutatz
Assignee: Felix Neutatz
Problem:
we experience some unexpected increase of data sent over the network for
broadcasts with increasing number of slots per Taskmanager.
We provided a benchmark [1]. It not only increases the size of data sent over
the network but also hurts performance as seen in the preliminary results
below. In this results cloud-11 has 25 nodes and ibm-power has 8 nodes with
scaling the number of slots per node from 1 - 16.
+-----------------------+--------------+-------------+
| suite | name | median_time |
+=======================+==============+=============+
| broadcast.cloud-11 | broadcast.01 | 8796 |
| broadcast.cloud-11 | broadcast.02 | 14802 |
| broadcast.cloud-11 | broadcast.04 | 30173 |
| broadcast.cloud-11 | broadcast.08 | 56936 |
| broadcast.cloud-11 | broadcast.16 | 117507 |
| broadcast.ibm-power-1 | broadcast.01 | 6807 |
| broadcast.ibm-power-1 | broadcast.02 | 8443 |
| broadcast.ibm-power-1 | broadcast.04 | 11823 |
| broadcast.ibm-power-1 | broadcast.08 | 21655 |
| broadcast.ibm-power-1 | broadcast.16 | 37426 |
+-----------------------+--------------+-------------+
After looking into the code base it, it seems that the data is de-serialized
only once per TM, but the actual data is sent for all slots running the
operator with broadcast vars and just gets discarded in case its already
de-serialized.
We do not see a reason the data can't be shared among the slots of a TM and
therefore just sent once.
[1] https://github.com/TU-Berlin-DIMA/flink-broadcast
This Jira will continue the discussion started here:
https://mail-archives.apache.org/mod_mbox/flink-dev/201606.mbox/%3c1465386300767.94...@tu-berlin.de%3E
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