public static PipeConsensusSyncLagManager getInstance(String groupId) {
    return PipeConsensusSyncLagManagerHolder.CONSENSU_GROUP_ID_2_INSTANCE_MAP.computeIfAbsent(
        groupId, key -> new PipeConsensusSyncLagManager());
  }
SyncLag represents the biggest difference between the current replica users' write progress and
the synchronization progress of all other replicas. The semantics is how much data the leader
has left to synchronize.
iotdb-core/consensus/src/main/java/org/apache/iotdb/consensus/pipe/metric/PipeConsensusSyncLagManager.java