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https://issues.apache.org/jira/browse/YARN-11907?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ryu Kobayashi reassigned YARN-11907:
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Assignee: Ryu Kobayashi
> FairSharePolicy: compareDemand() causes queue starvation for empty queues
> with pending apps
> -------------------------------------------------------------------------------------------
>
> Key: YARN-11907
> URL: https://issues.apache.org/jira/browse/YARN-11907
> Project: Hadoop YARN
> Issue Type: Bug
> Components: fairscheduler
> Reporter: Ryu Kobayashi
> Assignee: Ryu Kobayashi
> Priority: Major
>
> h3. Problem
> FairSharePolicy.compareDemand() assigns lowest priority to queues with
> demand=0, preventing progression to Stage 2 (minShare comparison). This
> causes severe queue starvation when a queue becomes empty but has
> applications waiting for
> ApplicationMaster allocation.
> h3. Reproduction Scenario
> A leaf queue with the following characteristics experiences starvation:
> * Queue becomes temporarily empty (all previous jobs complete)
> * New applications are submitted and enter ACCEPTED state
> * Queue has demand=0 (no running containers) but getNumRunnableApps() > 0
> (apps waiting for AM)
> * Other queues continue receiving AM allocations
> * The empty queue receives no AM allocations for extended periods (hours)
> Observed behavior:
> * Queue remains starved for 2+ hours
> * Multiple applications wait 100+ minutes for AM allocation
> * Cluster has available resources during this period
> * Other queues receive thousands of container allocations
> h3. Root Cause{*}{*}
> [FairSharePolicy.java|https://github.com/apache/hadoop/blob/rel/release-3.4.2/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/policies/FairSharePolicy.java#L119-L131]
> Lines 119-131:
> {code:java}
> private int compareDemand(Schedulable s1, Schedulable s2) {
> int res = 0;
> long demand1 = s1.getDemand().getMemorySize();
> long demand2 = s2.getDemand().getMemorySize();
> if ((demand1 == 0) && (demand2 > 0)) {
> res = 1; // Queue with demand=0 receives lowest priority
> } else if ((demand2 == 0) && (demand1 > 0)) {
> res = -1;
> }
> return res;
> } {code}
> When a queue has no running containers (demand=0) but has applications in
> ACCEPTED state waiting for AM allocation, the queue is assigned lowest
> priority in Stage 1 comparison and never progresses to Stage 2 (minShare
> comparison), making
> minResources configuration ineffective.
> h3. Why Configuration Cannot Solve This
> Setting minResources in fair-scheduler.xml does not prevent this starvation
> due to two issues:
> 1. Stage 1 blocks Stage 2: compareDemand() returns non-zero for empty queues,
> preventing progression to compareMinShareUsage()
> 2. MinShare calculation caps at demand: Even if reaching Stage 2, lines
> 136-141 cap minShare:
> long minShare1 = Math.min(s1.getMinShare().getMemorySize(),
> s1.getDemand().getMemorySize()); // When demand=0, minShare becomes 0
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