Hi Anand,

spilling using the io directories is only relevant for Flink's batch
processing. This happens, for example if you enable blocking data exchange
where the produced data cannot be kept in memory. Moreover, it is used by
many of Flink's out-of-core data structures to enable exactly this feature
(e.g. users are the MutableHashTable, the MergeIterator to combine sorted
ata which has been spilled or the SorterMerger to actually spill data).

In streaming Flink uses the RocksDB state backend to spill very large state
gracefully to disk. Thus, you would need to configure RocksDB in order to
control the spilling behaviour.

Cheers,
Till

On Mon, Oct 8, 2018 at 2:18 PM Kostas Kloudas <k.klou...@data-artisans.com>
wrote:

> Sorry, I forgot to cc’ Till.
>
> On Oct 8, 2018, at 2:17 PM, Kostas Kloudas <k.klou...@data-artisans.com>
> wrote:
>
> Hi Anand,
>
> I think that Till is the best person to answer your question.
>
> Cheers,
> Kostas
>
> On Oct 5, 2018, at 3:44 PM, anand.gopin...@ubs.com wrote:
>
> 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
>
> Visit our website at http://www.ubs.com
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