private RecoveredEditsWriter getRecoveredEditsWriter(TableName tableName, byte[] region,
    long seqId) throws IOException {
    RecoveredEditsWriter ret = writers.get(Bytes.toString(region));
    if (ret != null) {
      return ret;
    }
    ret = createRecoveredEditsWriter(tableName, region, seqId);
    if (ret == null) {
      return null;
    }
    LOG.trace("Created {}", ret.path);
    writers.put(Bytes.toString(region), ret);
    return ret;
  }
Get a writer and path for a log starting at the given entry. This function is threadsafe so
long as multiple threads are always acting on different regions.
@return null if this region shouldn't output any logs
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/RecoveredEditsOutputSink.java