apache/hadoop · error · IOException

Unmatched ')'

Error message

Unmatched ')'

What it means

When reduce() sees ')' it pops tokens backwards until the matching '('; if the stack empties first, there is a ')' with no opening '(' and it throws IOException("Unmatched ')'"). The canonical case is one closing parenthesis too many, e.g. inner(tbl("a"),tbl("b"))).

Source

Thrown at hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/join/Parser.java:462

    public String toString() {
      StringBuilder sb = new StringBuilder();
      sb.append(ident + "(");
      for (Node n : kids) {
        sb.append(n.toString() + ",");
      }
      sb.setCharAt(sb.length() - 1, ')');
      return sb.toString();
    }
  }

  private static Token reduce(Stack<Token> st, JobConf job) throws IOException {
    LinkedList<Token> args = new LinkedList<Token>();
    while (!st.isEmpty() && !TType.LPAREN.equals(st.peek().getType())) {
      args.addFirst(st.pop());
    }
    if (st.isEmpty()) {
      throw new IOException("Unmatched ')'");
    }
    st.pop();
    if (st.isEmpty() || !TType.IDENT.equals(st.peek().getType())) {
      throw new IOException("Identifier expected");
    }
    Node n = Node.forIdent(st.pop().getStr());
    n.parse(args, job);
    return new NodeToken(n);
  }

  /**
   * Given an expression and an optional comparator, build a tree of
   * InputFormats using the comparator to sort keys.
   */
  static Node parse(String expr, JobConf job) throws IOException {
    if (null == expr) {
      throw new IOException("Expression is null");
    }

View on GitHub (pinned to 2add963021)

Solutions

1. Balance parentheses — exactly one ')' per '('
2. Generate the expression with CompositeInputFormat.compose() instead of manual concatenation
3. Dry-run setFormat(job) client-side to catch it before submission

Example fix

// before
job.set("mapred.join.expr", "inner(tbl(F,/a),tbl(F,/b)))");

// after
job.set("mapred.join.expr", "inner(tbl(F,/a),tbl(F,/b))");

static void checkBalanced(String expr) {
  int depth = 0;
  boolean inQuote = false;
  for (char c : expr.toCharArray()) {
    if (c == '"') inQuote = !inQuote;
    else if (!inQuote && c == '(') depth++;
    else if (!inQuote && c == ')' && --depth < 0) throw new IllegalArgumentException("unmatched )");
  }
  if (depth != 0) throw new IllegalArgumentException("unbalanced parentheses");
}
checkBalanced(expr);
job.set("mapred.join.expr", expr);

try {
  new CompositeInputFormat<Object>().setFormat(job);
} catch (IOException e) {
  throw new IllegalArgumentException("unbalanced ')' in mapred.join.expr", e);
}

When it happens

Trigger: An extra trailing ')'; a stray ')' anywhere no function call is currently open; expressions assembled by concatenating fragments that each carry their own closer.

Common situations: Hand-balanced parentheses; composing an expression from per-source snippets like tbl(...) + "))" where the count drifts.

Related errors

• Identifier expected
• Missing ')'
• Expected ','
• Expected ','
• Unmatched ')'

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/e8005e8b151e9d41. Report an issue: GitHub.