public FileInfo.RoughFileInfo getRoughFileInfo(TsFileResource resource) {
    FileInfo.RoughFileInfo roughFileInfo = roughInfoMap.get(resource);
    if (roughFileInfo != null) {
      return roughFileInfo;
    }
    synchronized (globalRoughInfoCacheForCompaction) {
      roughFileInfo = globalRoughInfoCacheForCompaction.get(resource.getTsFileID());
    }
    if (roughFileInfo != null) {
      roughInfoMap.put(resource, roughFileInfo);
    }
    return roughFileInfo;
  }
The size of global compaction estimation rough file info cahce.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/compaction/selector/estimator/AbstractCompactionEstimator.java