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[core] Replace O(n*m) list dedup with HashSet-based O(n+m) in SnapshotReaderImpl #7333

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[core] Replace O(n*m) list dedup with HashSet-based O(n+m) in SnapshotReaderImpl #7333

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23 changes: 21 additions & 2 deletions paimon-core/src/main/java/org/apache/paimon/table/source/snapshot/SnapshotReaderImpl.java
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Original file line number Diff line number Diff line change
Expand Up @@ -526,8 +526,8 @@ private Plan toIncrementalPlan(
totalBuckets = beforeEntries.get(0).totalBuckets();
}

// deduplicate
beforeEntries.removeIf(dataEntries::remove);
// deduplicate: remove entries common to both lists
deduplicate(beforeEntries, dataEntries);

List<DataFileMeta> before =
beforeEntries.stream()
Expand Down Expand Up @@ -697,4 +697,23 @@ private Map<String, DeletionFile> toDeletionFiles(
}
return deletionFiles;
}

/**
* Remove entries common to both lists using HashSet for O(n+m) complexity instead of O(n*m)
* with List.remove().
*/
private static void deduplicate(
List<ManifestEntry> beforeEntries, List<ManifestEntry> dataEntries) {
Set<ManifestEntry> afterSet = new HashSet<>(dataEntries);
Set<ManifestEntry> commonEntries = new HashSet<>();
beforeEntries.removeIf(
entry -> {
if (afterSet.contains(entry)) {
commonEntries.add(entry);
return true;
}
return false;
});
dataEntries.removeAll(commonEntries);
}
}
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