private void removeOldInstances() {
    long oldestAllowedInstance = System.currentTimeMillis() - infoCacheTime.toMillis();
    instanceContext
        .entrySet()
        .removeIf(
            entry -> {
              long endTime = entry.getValue().getEndTime();
              return endTime != -1 && endTime <= oldestAllowedInstance;
            });
  }
Gets the info for the specified fragment instance.

<p>NOTE: this design assumes that only fragment instances that will eventually exist are
queried.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/fragment/FragmentInstanceManager.java