public void checkLogLowReplication(long checkInterval) {
    long now = EnvironmentEdgeManager.currentTime();
    if (now - lastTimeCheckLowReplication < checkInterval) {
      return;
    }
    // Will return immediately if we are in the middle of a WAL log roll currently.
    if (!rollWriterLock.tryLock()) {
      return;
    }
    try {
      lastTimeCheckLowReplication = now;
      if (doCheckLogLowReplication()) {
        requestLogRoll(LOW_REPLICATION);
      }
    } finally {
      rollWriterLock.unlock();
    }
  }
Returns true if we exceeded the slow sync roll threshold over the last check interval
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AbstractFSWAL.java