public void cacheInsertNodeIfNeeded(
      final WALEntryPosition walEntryPosition, final InsertNode insertNode) {
    // reduce memory usage
    if (hasPipeRunning) {
      lruCache.put(walEntryPosition, new Pair<>(null, insertNode));
    }
  }
This cache is used by {@link WALEntryPosition}.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/utils/WALInsertNodeCache.java