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From zentol <...@git.apache.org>
Subject [GitHub] flink pull request #4080: [FLINK-6798][docs] update old network buffer notic...
Date Wed, 07 Jun 2017 14:37:26 GMT
Github user zentol commented on a diff in the pull request:

    https://github.com/apache/flink/pull/4080#discussion_r120643661
  
    --- Diff: docs/monitoring/large_state_tuning.md ---
    @@ -94,21 +94,11 @@ When a savepoint is manually triggered, it may be in process concurrently
with a
     
     ## Tuning Network Buffers
     
    -The number of network buffers is a parameter that can currently have an effect on checkpointing
at large scale.
    -The Flink community is working on eliminating that parameter in the next versions of
Flink.
    -
    -The number of network buffers defines how much data a TaskManager can hold in-flight
before back-pressure kicks in.
    -A very high number of network buffers means that a lot of data may be in the stream network
channels when a checkpoint
    -is started. Because the checkpoint barriers travel with that data (see [description of
how checkpointing works](../internals/stream_checkpointing.html)),
    -a lot of in-flight data means that the barriers have to wait for that data to be transported/processed
before arriving
    -at the target operator.
    -
    -Having a lot of data in-flight also does not speed up the data processing as a whole.
It only means that data is picked up faster
    -from the data source (log, files, message queue) and buffered longer in Flink. Having
fewer network buffers means that
    -data is picked up from the source more immediately before it is actually being processed,
which is generally desirable.
    -The number of network buffers should hence not be set arbitrarily large, but to a low
multiple (such as 2x) of the
    -minimum number of required buffers.
    -
    +Before Flink 1.3, an increased number of network buffers also caused increased checkpointing
times since
    +keeping more in-flight data also meant that checkpoint barriers got delayed. Since Flink
1.3, the
    --- End diff --
    
    remove "also" for a better flow.


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