Return MergeObserver from IndexWriter.forceMergeDeletes() (#14515) #15378
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salvatorecampagna
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IndexWriter.forceMergeDeletes() now returns MergePolicy.MergeObserver instead of void, allowing applications to monitor merge progress and wait for completion. This enables coordination between merge completion and other application logic, and supports both synchronous (await) and asynchronous (CompletableFuture) waiting patterns. Key capabilities: - Query merge status: hasNewMerges(), numMerges() - Wait synchronously: await(), await(timeout, unit) - Wait asynchronously: awaitAsync() returns CompletableFuture<Void> - Inspect individual merges: getMerge(int) Changes: - Add MergePolicy.MergeObserver nested class - Update IndexWriter.forceMergeDeletes() methods to return MergeObserver - Update RandomIndexWriter to propagate return type - Add comprehensive tests (blocking/non-blocking modes, timeout handling) Backward compatible: existing code that ignores the return value continues to work without modification.
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Measure actual merge time in testForceMergeDeletesWithObserver and testMergeObserverAwaitWithTimeout, failing if merges take longer than 30 seconds. This helps detect stuck merges or performance regressions while being generous enough for slow CI machines. Both tests maintain their upper timeouts (implicit for await() and 10 minutes for await(timeout, unit)) to prevent indefinite hangs, but now also fail fast at 30 seconds if something is wrong.
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Summary
Changes
IndexWriter.forceMergeDeletes()to returnMergePolicy.MergeObserverinstead of void, allowing applications to monitor merge progress and wait for completion.Fixes #14515
Motivation
Currently when calling
forceMergeDeletes(false), there's no way to monitor whether merges were scheduled or wait for them to complete. This makes it difficult to coordinate merge completion with other operations or implement custom scheduling strategies.Changes
Added
MergePolicy.MergeObserveras a new public API with methods to:The observer is thread-safe and handles cases where no merges are needed.
Updated
IndexWriter.forceMergeDeletes()methods to return the observer instead of void. Also updatedRandomIndexWriterto propagate the new return type.Testing
Added 7 tests covering blocking and non-blocking modes, timeout handling, null spec cases, and bounds checking. All tests passed 500 iterations each with no failures.
Backward Compatibility
Fully backward compatible. Existing code that ignores the return value continues to work unchanged. Changing void to a return type is not a breaking change in Java.
Files Modified