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From "weijie.tong (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5975) Resource utilization
Date Mon, 20 Nov 2017 05:34:00 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16258824#comment-16258824

weijie.tong commented on DRILL-5975:

Thanks for your detail explanation of current model and the reason caused cpu overloaded.
That matches what I thought. Drill's assumption about resource is not real at actual scenario
as you pointed out. At Alibaba, we have other teams using Flink and Spark, both of the two
systems can reach a cpu utilization to 70%. To Drill, the best score we have achieved is 40%.
So far as I know, this is also the best result of Mapr .  So Drill really have some works
to do about the schedule. Here I have some different opinions about some points:

* What's the entity to schedule ?  The entity which consumes the memory and cpu is the target.
To Drill ,it's the MinorFragment. When the scheduler schedules the entity ,it can determine
which nodes have enough resource to match the requirement to assign work to them. This can

also answer the question do we need the query-level schedule. Query-level schedule is too
coarse to take this role. I have investigated what Impala does. I am not optimistic to see
better improvements. MinorFragment level schedule will let the system works as what cpu pipeline

* The RecordBatch will be first inserted into memory , if the memory is not enough , it will
be flushed into the disk. This the common solution to Flink and Spark. The allocated next
'stage' workers will consume the RecordBatch soon, maybe just from the memory destination.
What's more , the data will also work as stream model. The RecordBatchManager will take the
Sender's role to contact with the receiver and send out the RecordBatch consecutively. By
leveraging the DataTunnel's sendRecordBatch method, the throttling characteristic is also
retained. To be clear, this only happens at the exchange stage. I don't agree we are reinventing
Hive, this model is also what Flink and Spark follows.

   The current zk-queue based query level throttling is still needed to  protect the system
from overloaded queries.Some of what you summary will help us to do a good scheduler to estimate
a more accurate resource requirement to allocate.

> Resource utilization
> --------------------
>                 Key: DRILL-5975
>                 URL: https://issues.apache.org/jira/browse/DRILL-5975
>             Project: Apache Drill
>          Issue Type: New Feature
>    Affects Versions: 2.0.0
>            Reporter: weijie.tong
>            Assignee: weijie.tong
> h1. Motivation
> Now the resource utilization radio of Drill's cluster is not too good. Most of the cluster
resource is wasted. We can not afford too much concurrent queries. Once the system accepted
more queries with a not high cpu load, the query which originally is very quick will become
slower and slower.
> The reason is Drill does not supply a scheduler . It just assume all the nodes have enough
calculation resource. Once a query comes, it will schedule the related fragments to random
nodes not caring about the node's load. Some nodes will suffer more cpu context switch to
satisfy the coming query. The profound causes to this is that the runtime minor fragments
construct a runtime tree whose nodes spread different drillbits. The runtime tree is a memory
pipeline that is all the nodes will stay alone the whole lifecycle of a query by sending out
data to upper nodes successively, even though some node could run quickly and quit immediately.What's
more the runtime tree is constructed before actual running. The schedule target to Drill will
become the whole runtime tree nodes.
> h1. Design
> It will be hard to schedule the runtime tree nodes as a whole. So I try to solve this
by breaking the runtime cascade nodes. The graph below describes the initial design. !https://raw.githubusercontent.com/wiki/weijietong/drill/images/design.png!
   [graph link|https://raw.githubusercontent.com/wiki/weijietong/drill/images/design.png]
> Every Drillbit instance will have a RecordBatchManager which will accept all the RecordBatchs
written by the senders of local different MinorFragments. The RecordBatchManager will hold
the RecordBatchs in memory firstly then disk storage . Once the first RecordBatch of a MinorFragment
sender of one query occurs , it will notice the FragmentScheduler. The FragmentScheduler is
instanced by the Foreman.It holds the whole PlanFragment execution graph.It will allocate
a new corresponding FragmentExecutor to run the generated RecordBatch. The allocated FragmentExecutor
will then notify the corresponding FragmentManager to indicate that I am ready to receive
the data. Then the FragmentManger will send out the RecordBatch one by one to the corresponding
FragmentExecutor's receiver like what the current Sender does by throttling the data stream.
> What we can gain from this design is :
> a. The computation leaf node does not to wait for the consumer's speed to end its life
to release the resource.
> b. The sending data logic will be isolated from the computation nodes and shared by different
> c. We can schedule the MajorFragments according to Drillbit's actual resource capacity
at runtime.
> d. Drill's pipeline data processing characteristic is also retained.
> h1. Plan
> This will be a large PR ,so I plan to divide it into some small ones.
> a. to implement the RecordManager.
> b. to implement a simple random FragmentScheduler and the whole event flow.
> c. to implement a primitive FragmentScheduler which may reference the Sparrow project.

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