apache/iceberg · error · UnsupportedOperationException

AlwaysTrue is a placeholder only

Error message

AlwaysTrue is a placeholder only

What it means

AlwaysTrue in ParquetFilters is only a placeholder FilterPredicate used as an identity marker when converting expressions; it is never a real filter to be evaluated. Calling its accept(Visitor) method always throws UnsupportedOperationException because no visitor evaluation is defined for it.

Solutions

  1. Do not use AlwaysTrue as an actual filter — use FilterApi alwaysTrue() from parquet-mr's FilterApi if a real always-match filter is needed
  2. Treat AlwaysTrue in converted output as a signal to skip filtering entirely rather than feeding it to a visitor

Example fix

// before
FilterPredicate p = ParquetFilters.predicate(Expressions.alwaysTrue());
visitor.visit(p); // throws
// after
FilterPredicate p = FilterApi.alwaysTrue(); // real parquet-mr filter
Defensive patterns

Strategy: type-guard

Validate before calling

if (pred instanceof ParquetFilters.AlwaysTrue) { /* skip filtering: match all rows */ }

Type guard

static boolean isPlaceholder(FilterPredicate p) {
  return p instanceof ParquetFilters.AlwaysTrue || p instanceof ParquetFilters.AlwaysFalse;
}

Try / catch

if (!isPlaceholder(pred)) {
  visitor.visit(pred);
} else {
  // handle sentinel explicitly, never call accept()
}

Prevention

When it happens

Trigger: Passing ParquetFilters.AlwaysTrue.INSTANCE to a Parquet FilterPredicate Visitor (e.g. LogicalFilterPredicate composition or parquet-mr's FilterPredicate visitor evaluation), which invokes accept().

Common situations: Manually composing Parquet filters with and()/or() using the sentinel; running parquet-mr's filter evaluation against a converted predicate that collapsed to AlwaysTrue.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/ef54e7fd05d30d2f. Report an issue: GitHub.

Appendix: source

Thrown at parquet/src/main/java/org/apache/iceberg/parquet/ParquetFilters.java:242

    // TODO: this needs to convert to handle BigDecimal and UUID
    Object value = lit.value();
    if (value instanceof Number) {
      return (C) lit.value();
    } else if (value instanceof CharSequence) {
      return (C) Binary.fromString(value.toString());
    } else if (value instanceof ByteBuffer) {
      return (C) Binary.fromReusedByteBuffer((ByteBuffer) value);
    }
    throw new UnsupportedOperationException(
        "Type not supported yet: " + value.getClass().getName());
  }

  private static class AlwaysTrue implements FilterPredicate {
    static final AlwaysTrue INSTANCE = new AlwaysTrue();

    @Override
    public <R> R accept(Visitor<R> visitor) {
      throw new UnsupportedOperationException("AlwaysTrue is a placeholder only");
    }
  }

  private static class AlwaysFalse implements FilterPredicate {
    static final AlwaysFalse INSTANCE = new AlwaysFalse();

    @Override
    public <R> R accept(Visitor<R> visitor) {
      throw new UnsupportedOperationException("AlwaysFalse is a placeholder only");
    }
  }
}

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