HDDS-16216. Avoid the flatten-copy in KeyInputStream.getBlockLocationInfo

[0lai0]

What changes were proposed in this pull request?

KeyInputStream.getBlockLocationInfo runs on every per-block pipeline refresh / read retry. It flatten-copies the version map with createLocationList(), then does stream().filter().collect(toList()) just to pick get(0), two throwaway ArrayLists per call, no short-circuit.

OmKeyLocationInfoGroup.createLocationList() is documented a s"expensive ... Use getLocationLists() instead".

Fix: iterate getLocationLists() (the raw uncopied Collection<List<...>>) with a nested for-loop, return on first match. Zero allocations, short-circuits, same semantics.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-16216

How was this patch tested?

https://github.com/0lai0/ozone/actions/runs/32735325487

• mvn -pl :ozone-client install -DskipTests — pass
• mvn -pl :ozone-client test -Dtest=TestKeyInputStreamEC — pass
• mvn -pl :ozone-client checkstyle:check — pass

Local JMH (target at last position → worst-case scan, gains are purely from removed allocations):

N / G	before ns	after ns	before B/op	after B/op
1 / 1	91	4	816	≈0
1 / 4	131	11	1,080	≈0
16 / 1	144	9	1,000	≈0
16 / 4	288	33	1,944	≈0
128 / 1	395	40	2,808	≈0
128 / 4	1,365	158	7,760	≈0

Generated-by: Claude Code (claude-opus-4-7)

[yandrey321]

lgtm

[Copilot]

Pull request overview

Optimizes block-location lookup by avoiding flattening, temporary allocations, and unnecessary stream processing.

Changes:

• Uses short-circuiting nested iteration over location lists.
• Restricts commons-collections4 to test scope.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
hadoop-ozone/client/src/main/java/org/apache/hadoop/ozone/client/io/KeyInputStream.java	Replaces stream-based lookup with direct allocation-free iteration.
hadoop-ozone/client/pom.xml	Adjusts the Commons Collections dependency scope.

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