FrankYang0529 commented on PR #561:
URL: https://github.com/apache/yunikorn-core/pull/561#issuecomment-1587587529
I tried to run `TestTryAllocatePreemptNode` multiple time and compared logs
between expected and unexpected results. I found the different part is
following:
```
# expected
2023-06-12T16:49:19.170+0800 DEBUG objects/preemption.go:352 No
RM callback plugin registered, using first selected node for preemption
{"NodeID": "node1", "AllocationKey": "alloc3"}
# unexpected
2023-06-12T22:58:18.571+0800 DEBUG objects/preemption.go:352 No
RM callback plugin registered, using first selected node for preemption
{"NodeID": "node2", "AllocationKey": "alloc3"}
```
Above logs are from the following code, so I checked how we get
`predicateChecks`.
https://github.com/apache/yunikorn-core/blob/d2d7ce89457cbbce140e2737098ae62f6a9d8fee/pkg/scheduler/objects/preemption.go#L351-L354
We get `predicateChecks` by for-loop `p.nodeAvailableMap` and find fit nodes
as following:
https://github.com/apache/yunikorn-core/blob/d2d7ce89457cbbce140e2737098ae62f6a9d8fee/pkg/scheduler/objects/preemption.go#L485-L512
The problem is that Golang doesn't guarantee key order in map (we can run
[this](https://go.dev/play/p/IEYV9Vy22wx) to check it). If we get `node2` first
and it has same `StartIndex` with `node1`, we will preempt `node2`.
https://github.com/apache/yunikorn-core/blob/d2d7ce89457cbbce140e2737098ae62f6a9d8fee/pkg/scheduler/objects/preemption.go#L342-L345
My suggestion is that we can sort by `NodeID` if `StartIndex` are same.
cc @craigcondit @pbacsko @zhuqi-lucas.
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