apache/hadoop · error · IOException

Identifier expected

Error message

Identifier expected

What it means

After popping back to '(', reduce() requires the next token down the stack to be the operator identifier (TType.IDENT). A '(' with no function name before it throws IOException("Identifier expected") — the common case is wrapping the whole expression in redundant parentheses, since the grammar supports function calls only: parentheses are always calls, never grouping.

Source

Thrown at hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/join/Parser.java:466

      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");
    }
    Class<? extends WritableComparator> cmpcl =
      job.getClass("mapred.join.keycomparator", null, WritableComparator.class);
    Lexer lex = new Lexer(expr);
    Stack<Token> st = new Stack<Token>();

View on GitHub (pinned to 2add963021)

Solutions

1. Remove redundant parentheses — every '(' must directly follow an operator identifier
2. Nest inner calls as arguments instead of grouping them with parens
3. Dry-run setFormat(job) client-side

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))");

// the grammar is function calls only: every '(' must directly follow an identifier
if (expr.matches(".*(^|[^a-zA-Z0-9_$.])\\(")) {
  throw new IllegalArgumentException(
      "'(' without an operator name; remove grouping parentheses");
}
job.set("mapred.join.expr", expr);

try {
  new CompositeInputFormat<Object>().setFormat(job);
} catch (IOException e) {
  throw new IllegalArgumentException(
      "no grouping parens in join expressions; every '(' needs an operator name before it", e);
}

When it happens

Trigger: (inner(tbl("a"),tbl("b"))) — outer redundant parens; a nested '(' immediately after another '(' as in inner((tbl("a")),...); a quoted string or number directly before '('.

Common situations: Wrapping the expression in parens 'for safety'; formatting or indentation edits that insert parentheses; assuming algebraic grouping is allowed.

Related errors

• Unmatched ')'
• Missing ')'
• Expected ','
• Expected ','
• Unmatched ')'

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/4d35b21a8677812c. Report an issue: GitHub.