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https://issues.apache.org/jira/browse/DRILL-7607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17049904#comment-17049904
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ASF GitHub Bot commented on DRILL-7607:
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weijietong commented on issue #2000: DRILL-7607: Support dynamic credit based
flow control
URL: https://github.com/apache/drill/pull/2000#issuecomment-593767181
Still on a pre-product stage at our env. But as I mentioned above , we could
give a query a hint to open this feature not apply to all the queries, so
queries like `select user_id ` will benefit from this feature. Also we normally
push down query to our storage, so the query execution level will not suffer
from large data batch transfer . It's different from systems based on parquet
and HDFS plugin. So we also expect the query execution level to accept data
more rapidly from the storage plugin to release the storage server resource as
soon as possible. Otherwise the storage server level's execution pipeline will
not be closed until the query level finished sending out all its data.
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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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