private byte[] startOf(HStoreFile sf) {
    byte[] result = fileStarts.get(sf);

    // result and INVALID_KEY_IN_MAP are compared _only_ by reference on purpose here as the latter
    // serves only as a marker and is not to be confused with other empty byte arrays.
    // See Javadoc of INVALID_KEY_IN_MAP for more information
    return (result == null) ? sf.getMetadataValue(STRIPE_START_KEY)
      : result == INVALID_KEY_IN_MAP ? INVALID_KEY
      : result;
  }
Finds the stripe index for the stripe containing a row provided externally for get/scan.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StripeStoreFileManager.java