Fix race condition in LuceneIndex GraphDirectory during store#628
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Fix race condition in LuceneIndex GraphDirectory during store#628
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…ization Lucene's default ConcurrentMergeScheduler runs background merge threads that modify the GraphDirectory's fileEntries map concurrently with GigaMap#store, causing BinaryPersistenceException with inconsistent element counts. Use SerialMergeScheduler when GraphDirectory is active to ensure merges run on the caller's thread under the GigaMap lock.
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Pull request overview
Fixes a concurrency issue when using the in-graph Lucene GraphDirectory by preventing Lucene from mutating the persistent fileEntries map from background merge threads during GigaMap serialization.
Changes:
- Refactors
lazyInit()to build a reusableIndexWriterConfigand conditionally configure aSerialMergeScheduler. - Introduces
usesGraphDirectory()and simplifiescreateDirectory()to centralize the “in-graph vs external directory” decision.
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zdenek-jonas
approved these changes
Mar 30, 2026
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This pull request refactors the initialization logic for the Lucene index in
LuceneIndex.java, primarily to improve clarity and ensure thread safety when using aGraphDirectory. The main changes involve extracting logic for determining directory type and configuring merge schedulers to prevent concurrency issues.Initialization and thread safety improvements:
GraphDirectoryis used into a newusesGraphDirectory()method, improving readability and maintainability.createDirectory()to useusesGraphDirectory(), clarifying the choice betweenGraphDirectoryand a custom directory creator.lazyInit(), when using aGraphDirectory, configured theIndexWriterConfigto use aSerialMergeSchedulerinstead of the defaultConcurrentMergeScheduler, ensuring merges run on the caller's thread and preventing race conditions with GigaMap serialization.These changes help ensure that Lucene index merges are handled safely in environments where background thread concurrency could cause data corruption or race conditions.