Nemesis123925 opened a new pull request, #12029:
URL: https://github.com/apache/pinot/pull/12029
## Setup:
Java version: openjdk 11.0.20.1
Maven version: Apache Maven 3.8.1
## Fixed Test:
`org.apache.pinot.core.transport.server.routing.stats.ServerRoutingStatsManagerTest.testQuerySubmitAndCompletionStats`
## Test Failure:
The test's `List<Pair<String, Integer>>` generated by
`fetchNumInFlightRequestsForAllServers()`, `fetchEMALatencyForAllServers()`,
and `fetchHybridScoreForAllServers()` shows non-determinism with the order of
`Pair<String, Integer>` when applying the `NonDex` tool. Although the content
of the Assertion is all correct, the assertion could assert on wrong index in
the `List` due to the non-determinism in the `List`. One example could be the
`List` contatins `{Pair("server1", 1), Pair("server2", 2)}`, but the assertion
assert that the `List` is `{Pair("server2", 2), Pair("server1", 1)}`.
## Root Cause:
The root cause is in the `ConcurrentHashMap` used by
[`ServerRoutingStatsManager.java`'s
`_serverQueryStatsMap`](https://github.com/apache/pinot/blob/7217bb9d16b60074c1e9a9df72984556a7c8dbd5/pinot-core/src/main/java/org/apache/pinot/core/transport/server/routing/stats/ServerRoutingStatsManager.java#L50),
which got iterated to create the `List` using the `entrySet()` function in
[`fetchNumInFlightRequestsForAllServers`](https://github.com/apache/pinot/blob/7217bb9d16b60074c1e9a9df72984556a7c8dbd5/pinot-core/src/main/java/org/apache/pinot/core/transport/server/routing/stats/ServerRoutingStatsManager.java#L248),
[`fetchEMALatencyForAllServers`](https://github.com/apache/pinot/blob/7217bb9d16b60074c1e9a9df72984556a7c8dbd5/pinot-core/src/main/java/org/apache/pinot/core/transport/server/routing/stats/ServerRoutingStatsManager.java#L293),
and
[`fetchHybridScoreForAllServers`](https://github.com/apache/pinot/blob/7217bb9d16b60074c1e9a9df72984556a7c8dbd5/pinot-core/src/main/java/org/apache
/pinot/core/transport/server/routing/stats/ServerRoutingStatsManager.java#L339).
The `List<Pair<String, Interger>>` created is directly returned to the
`testQuerySubmitAndCompletionStats`, which cause the order's non-determinism in
the `List`.
## Fix:
Since the specific part suffering from the non-determinism here only have
two elements in the `List`, the fix here is to first found the element's index
(`0` or `1`) before asserting them. This eleminates the non-determinism here
without modifing the source code in `main` folder.
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