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https://issues.apache.org/jira/browse/DRILL-7607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17046554#comment-17046554
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ASF GitHub Bot commented on DRILL-7607:
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weijietong commented on pull request #2000: DRILL-7607: support dynamic credit
based flow control
URL: https://github.com/apache/drill/pull/2000
# [DRILL-7607](https://issues.apache.org/jira/browse/DRILL-7607): support
dynamic credit based flow control
## Description
change the static credit based flow control to dynamic credit based flow
control.
The logic is as below:
Initially, the sender sends the batch according to the initial static sender
semaphore. After the receiver receives enough data ,it calculates the runtime
credit value , sends the runtime credit value to the sender as the ACK
response. Then the sender receives this runtime credit value, changes to this
runtime credit value from the initial credit value.
The runtime generated credit value will only be generated one time. It will
not be changed again to make the flow control logic simple.
The ACK response credit value has three type numeric value with different
meaning:
-1 : meaning ACK for a fail response
0 : no runtime credit value to suggest to the sender , the sender still
sends its data as its initial static credit value(current: 3)
value > 0 : meaning a suggested runtime credit value from the receiver.
## Documentation
NO
## Testing
TestBitRpc,testConnectionBackpressure
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> Dynamic credit based flow control
> ---------------------------------
>
> Key: DRILL-7607
> URL: https://issues.apache.org/jira/browse/DRILL-7607
> Project: Apache Drill
> Issue Type: New Feature
> Components: Server, Execution - RPC
> Affects Versions: 1.17.0
> Reporter: Weijie Tong
> Assignee: Weijie Tong
> Priority: Major
> Fix For: 1.18.0
>
>
> Drill current has a static credit based flow control between the batch sender
> and receiver. That means ,all the sender send out their batch through the
> DataTunnel by a static 3 semaphore. To the receiver side , there's two cases,
> the UnlimitedRawBatchBuffer has a 6 * fragmentCount receiver semaphore, the
> SpoolingRawBatchBuffer acts as having unlimited receiving semaphore as it
> could flush data to disk.
> The static credit has the following weak points:
> 1. While the send batch data size is low(e.g. it has only one column bigint
> data) and the receiver has larger memory space, the sender still could not
> send out its data rapidly.
> 2. As the static credit assumption does not set the semaphore number
> according to the corresponding receiver memory space, it still have the risk
> to make the receiver OOM.
> 3. As the sender semaphore is small, it could not send its batch
> consecutively due to wait for an Ack to release one semaphore , and then ,
> the sender's corresponding execution pipeline would be halt, also the same to
> its leaf execution nodes.
> The dynamic credit based flow control could solve these problems. It starts
> from the static credit flow control. Then the receiver collects some batch
> datas to calculate the average batch size. According to the receiver side
> memory space, the receiver make a runtime sender credit and receiver side
> total credit. The receiver sends out the runtime sender credit number to the
> sender by the Ack response. The sender change to the runtime sender credit
> number when receives the Ack response with a runtime credit value.
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