Improve assignmentMetadataStore thread safety #3020
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junkaixue
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Apr 30, 2025
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| return _globalBaseline.entrySet().stream().collect( | ||
| Collectors.toMap(Map.Entry::getKey, | ||
| entry -> new ResourceAssignment(entry.getValue().getRecord()))); |
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Try not implementing lambda function in core piece. It hurts the performance.
GrantPSpencer
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junkaixue
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May 23, 2025
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| Map<String, ResourceAssignment> result = new HashMap<>(_bestPossibleAssignment); | ||
| for (Map.Entry<String, ResourceAssignment> entry : _bestPossibleAssignment.entrySet()) { | ||
| result.put(entry.getKey(), new ResourceAssignment(entry.getValue().getRecord())); | ||
| } |
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_bestPossibleAssignment.size()?
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And this logic I have seen for multiple lines. Please make them in a function to be called in the place similar.
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Issues
ConcurrentModification errors can occur during waged rebalance due to async thread modifying the best possible while the main thread is iterating over it
Description
This PR refactors how we access and store the best possible and baseline assignments.
Get - returns a deep copy, assignment can now be safely modified without affecting the cache
Set - creates a deep copy prior to storing - the passed in assignment can be safely modified without affecting the cache
The above changes are aimed at preventing unintended modification of the underlying ResourceAssignments
When a new assignment is persisted, we no longer clear the previous map and add the new map's value, but just point
_globalBaseline or _bestPossibleAssignment at the new map. This change is intended to isolate threads so they cannot modify the underlying structure that another thread is pointing at.
Stack trace of concurrentModification exception that can occur:
Tests
The following tests are written for this issue:
No new tests were added
The following is the result of the "mvn test" command on the appropriate module:
Changes that Break Backward Compatibility (Optional)
N/A
Commits
Code Quality
(helix-style-intellij.xml if IntelliJ IDE is used)