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https://issues.apache.org/jira/browse/FLINK-15013?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16986656#comment-16986656
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Zhu Zhu commented on FLINK-15013:
---------------------------------
Thanks for [~aljoscha] to find out the faulty commit.
The root cause should be this change in the faulty commit:
- int bestCandidateScore = Integer.MIN_VALUE;
+ double bestCandidateScore = Double.MIN_VALUE;
Since Integer.MIN_VALUE is negative but Double.MIN_VALUE is a very small
positive value. So that slot with core 0(Locality==NON_LOCAL) will fail to
match the slot request.
*change it to {{double bestCandidateScore = -1.0;}} should fix this issue.*
However, here comes another question: the {{NON_LOCAL}} locality should not
happen in this case. Theoretically it should be able to find a slot of its
upstream node which is {{LOCAL}}, since the task is scheduled when its upstream
tasks are assigned slots, its parallelism is not larger, and all tasks are in
the same slot sharing group.
I did some experiment and find the cause, it's a bit complicated to explain.
1. To be simple, the root cause is that a slot offer for a shared slot
completes the location of inner tasks before making the shared slot resolved
with location. (due to unexpected {{CompletableFuture}} callback)
2. The task location completion triggers its downstream task scheduling, but
the downstream task would fail to see resolved shared slot of its upstream task
due to #1. So it make pick a random pending slot sharing group which is against
the input locality constraint. (see {{SchedulerImpl#allocateMultiTaskSlot}})
3. After #2 happened. A later scheduled task may find there is no pending slot
sharing group, and the resolved slot sharing group cannot fulfill its locality
constraint. Then it will request a new slot.
Looks to me the most simple way to fix it would be: Resolve shared slot
locations when it's assigned a physical slot, before completing the location
futures of tasks. So that the tasks would always be possible to find a resolved
slot.
Not that this may not be a new issue since the problematic logics has been
there for versions. Fixing it is not necessary to resolve this ticket, but can
make the input locality constraint work as expected.
> Flink (on YARN) sometimes needs too many slots
> ----------------------------------------------
>
> Key: FLINK-15013
> URL: https://issues.apache.org/jira/browse/FLINK-15013
> Project: Flink
> Issue Type: Bug
> Components: Runtime / Coordination
> Affects Versions: 1.10.0
> Reporter: Aljoscha Krettek
> Priority: Blocker
> Fix For: 1.10.0
>
> Attachments: DualInputWordCount.jar
>
>
> *THIS IS DIFFERENT FROM FLINK-15007, even though the text looks almost the
> same.*
> This was discovered while debugging FLINK-14834. In some cases a Flink needs
> needs more slots to execute than expected. You can see this in some of the
> logs attached to FLINK-14834.
> You can reproduce this using
> [https://github.com/aljoscha/docker-hadoop-cluster] to bring up a YARN
> cluster and then running a compiled Flink in there.
> When you run
> {code:java}
> bin/flink run -m yarn-cluster -p 3 -yjm 1224 -ytm 1224
> /root/DualInputWordCount.jar --input hdfs:///wc-in-1 --output hdfs:///wc-out
> && hdfs dfs -rm -r /wc-out
> {code}
> and check the logs afterwards you will sometimes see three "Requesting new
> slot..." statements and sometimes you will see four.
> This is the {{git bisect}} log that identifies the first faulty commit
> ([https://github.com/apache/flink/commit/2ab8b61f2f22f1a1ce7f92cd6b8dd32d2c0c227d|https://github.com/apache/flink/commit/2ab8b61f2f22f1a1ce7f92cd6b8dd32d2c0c227d]):
> {code:java}
> git bisect start
> # good: [09f2f43a1d73c76bf4d3f4a1205269eb860deb14] [FLINK-14154][ml] Add the
> class for multivariate Gaussian Distribution.
> git bisect good 09f2f43a1d73c76bf4d3f4a1205269eb860deb14
> # bad: [01d6972ab267807b8afccb09a45c454fa76d6c4b] [hotfix] Refactor out slots
> creation from the TaskSlotTable constructor
> git bisect bad 01d6972ab267807b8afccb09a45c454fa76d6c4b
> # bad: [7a61c582c7213f123e10de4fd11a13d96425fd77] [hotfix] Fix wrong Java doc
> comment of BroadcastStateBootstrapFunction.Context
> git bisect bad 7a61c582c7213f123e10de4fd11a13d96425fd77
> # good: [edeec8d7420185d1c49b2739827bd921d2c2d485] [hotfix][runtime] Replace
> all occurrences of letter to mail to unify wording of variables and
> documentation.
> git bisect good edeec8d7420185d1c49b2739827bd921d2c2d485
> # bad: [1b4ebce86b71d56f44185f1cb83d9a3b51de13df]
> [FLINK-14262][table-planner-blink] support referencing function with
> fully/partially qualified names in blink
> git bisect bad 1b4ebce86b71d56f44185f1cb83d9a3b51de13df
> # good: [25a3d9138cd5e39fc786315682586b75d8ac86ea] [hotfix] Move
> TaskManagerSlot to o.a.f.runtime.resourcemanager.slotmanager
> git bisect good 25a3d9138cd5e39fc786315682586b75d8ac86ea
> # good: [362d7670593adc2e4b20650c8854398727d8102b] [FLINK-12122] Calculate
> TaskExecutorUtilization when listing available slots
> git bisect good 362d7670593adc2e4b20650c8854398727d8102b
> # bad: [7e8218515baf630e668348a68ff051dfa49c90c3]
> [FLINK-13969][Checkpointing] Do not allow trigger new checkpoitn after stop
> the coordinator
> git bisect bad 7e8218515baf630e668348a68ff051dfa49c90c3
> # bad: [269e7f007e855c2bdedf8bad64ef13f516a608a6] [FLINK-12122] Choose
> SlotSelectionStrategy based on ClusterOptions#EVENLY_SPREAD_OUT_SLOTS_STRATEGY
> git bisect bad 269e7f007e855c2bdedf8bad64ef13f516a608a6
> # bad: [2ab8b61f2f22f1a1ce7f92cd6b8dd32d2c0c227d] [FLINK-12122] Add
> EvenlySpreadOutLocationPreferenceSlotSelectionStrategy
> git bisect bad 2ab8b61f2f22f1a1ce7f92cd6b8dd32d2c0c227d
> # first bad commit: [2ab8b61f2f22f1a1ce7f92cd6b8dd32d2c0c227d] [FLINK-12122]
> Add EvenlySpreadOutLocationPreferenceSlotSelectionStrategy
> {code}
> I'm using the streaming WordCount example that I modified to have two
> "inputs", similar to how the WordCount example is used in the
> YARN/kerberos/Docker test. Instead of using the input once we use it like
> this:
> {code}
> text =
> env.readTextFile(params.get("input")).union(env.readTextFile(params.get("input")));
> {code}
> to create two inputs from the same path. A jar is attached.
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