public long getOldestSeqIdOfStore(byte[] familyName) {
    return wal.getEarliestMemStoreSeqNum(getRegionInfo().getEncodedNameAsBytes(), familyName);
  }
Returns the latest sequence number that was read from storage when this region was opened
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java