Method prefixKeyWithSalt

src/core/RowKey.java:141–167

Calculates and writes an array of one or more salt bytes at the front of the given row key. The salt is calculated by taking the Java hash code of the metric and tag UIDs and returning a modulo based on the number of salt buckets. The result will always be a positive integer from 0 to salt buckets.

(final byte[] row_key)

   * @since 2.2
   */
  public static void prefixKeyWithSalt(final byte[] row_key) {
    if (Const.SALT_WIDTH() > 0) {
      if (row_key.length < (Const.SALT_WIDTH() + TSDB.metrics_width()) || 
        (Bytes.memcmp(row_key, new byte[Const.SALT_WIDTH() + TSDB.metrics_width()], 
            Const.SALT_WIDTH(), TSDB.metrics_width()) == 0)) {
        // ^ Don't salt the global annotation row, leave it at zero
        return;
      }
      final int tags_start = Const.SALT_WIDTH() + TSDB.metrics_width() + 
          Const.TIMESTAMP_BYTES;
      
      // we want the metric and tags, not the timestamp
      final byte[] salt_base = 
          new byte[row_key.length - Const.SALT_WIDTH() - Const.TIMESTAMP_BYTES];
      System.arraycopy(row_key, Const.SALT_WIDTH(), salt_base, 0, TSDB.metrics_width());
      System.arraycopy(row_key, tags_start,salt_base, TSDB.metrics_width(), 
          row_key.length - tags_start);
      int modulo = Arrays.hashCode(salt_base) % Const.SALT_BUCKETS();
      if (modulo < 0) {
        // make sure we return a positive salt.
        modulo = modulo * -1;
      }
    
      final byte[] salt = getSaltBytes(modulo);
      System.arraycopy(salt, 0, row_key, 0, Const.SALT_WIDTH());
    } // else salting is disabled so it's a no-op
  }

  /**
   * Checks a row key to determine if it contains the metric UID. If salting is