Make virtual group assignment for FaultZoneBasedVirtualGroupAssignmentAlgorithm deterministic

[nisargthakkar]

Issues

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  • Fixes Virtual group calculation in FaultZoneBasedVirtualGroupAssignmentAlgorithm is non-deterministic #3057

Description

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When using FaultZoneBasedVirtualGroupAssignmentAlgorithm, the topology assignment is not deterministic because it only uses instance counts within fault zones as a decider of zone weight. However, when multiple fault zones have the same number of instances, the fault zone that gets picked through a priority queue depends on the internal implementation on the order in which the fault zones were added to the priority queue, and the Java version that is being used. The impact of this is that service restarts could lead to a different virtual topology grouping and that triggers data rebalance.

Tests

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  • TestFaultZoneBasedVirtualGroupAssignment#testDeterministicVirtualZoneAssignment

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Code Quality

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[nisargthakkar]

Thank you for the review. The PR is approved by @xyuanlu and @junkaixue. This PR is ready to be merged. Final commit message: "Make virtual group assignment for FaultZoneBasedVirtualGroupAssignmentAlgorithm deterministic".