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flink memory management / temp-io dir question


Hi ,

I had a question with respect flink memory management / overspill to /tmp.

 

In the docs (https://ci.apache.org/projects/flink/flink-docs-release-1.6/ops/config.html#configuring-temporary-io-directories) it says: Although Flink aims to process as much data in main memory as possible, it is not uncommon that more data needs to be processed than memory is available. Flink’s runtime is designed to write temporary data to disk to handle these situations....

 

In a  flink job  that processes a couple streams of 1M events in a  windowed co group function with parallelism 8 - we see 8 dirs created in /tmp with 100s of Meg of data, the name of each dir seems aligned to the data for each parallel thread windowing against the co-group  operator

 

e.g.

bash-4.2$ du -sh *

0       flink-dist-cache-a4a69215-665a-4c3c-8d90-416cbe192f26

352M    flink-io-9033517c-ac92-4baa-9e59-79bc80c72a9e

4.0K    localState

7.2M    rocksdb-lib-03d9460b15e6bf6af4f3d9b0ff7980c3

 

bash-4.2$ du -sh flink-io-9033517c-ac92-4baa-9e59-79bc80c72a9e/*

...

36M     flink-io-9033517c-ac92-4baa-9e59-79bc80c72a9e/job_cf2dca7843dd6b6296aa1a9d15a1d435_op_WindowOperator_014556c228cb5344d41861769d2bbbc1__1_8__uuid_93307150-4f62-4b06-a71e-0230360f7d86

36M     flink-io-9033517c-ac92-4baa-9e59-79bc80c72a9e/job_cf2dca7843dd6b6296aa1a9d15a1d435_op_WindowOperator_014556c228cb5344d41861769d2bbbc1__2_8__uuid_7b2f8957-7044-4bb3-869e-28843bd737a1

36M     flink-io-9033517c-ac92-4baa-9e59-79bc80c72a9e/job_cf2dca7843dd6b6296aa1a9d15a1d435_op_WindowOperator_014556c228cb5344d41861769d2bbbc1__3_8__uuid_54306a44-7e06-45ae-ba0e-4649887bca7e

...

 

I was wondering can / should this 'over spill' be avoided by increasing the heap of the task manager or another config or should I not worry about it?

Is there more information/docs on how this data is used/ cleaned up & what is the cost of this overspill to latency/ checkpointing? Any impact I should be aware of?

 

thanks

Anand

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