apache/iceberg · error · IllegalArgumentException

Invalid base type for decimal

Error message

Invalid base type for decimal: %s

What it means

Validation in ParquetAvro's decimal schema modifier: the Avro base type carrying the decimal logical type must be int (precision<=9), long (precision<=18), fixed, or binary — the default branch rejects any other base. The %s is the schema type; it fires while preparing an Avro-to-Parquet decimal conversion with an incompatible base type.

Solutions

1. Store the decimal over binary/fixed or an int/long sized for the precision
2. Regenerate the Avro schema with a valid decimal base type
3. Validate precision vs base type before conversion

When it happens

Trigger: Thrown at parquet/src/main/java/org/apache/iceberg/parquet/ParquetAvro.java:98 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/4666431432aa62de. Report an issue: GitHub.

Appendix: source

Thrown at parquet/src/main/java/org/apache/iceberg/parquet/ParquetAvro.java:98

      return schema;
    }

    @Override
    public void validate(Schema schema) {
      super.validate(schema);
      switch (schema.getType()) {
        case INT:
          Preconditions.checkArgument(
              precision <= 9, "Int cannot hold decimal precision: %s", precision);
          break;
        case LONG:
          Preconditions.checkArgument(
              precision <= 18, "Long cannot hold decimal precision: %s", precision);
          break;
        case FIXED:
          break;
        default:
          throw new IllegalArgumentException("Invalid base type for decimal: " + schema);
      }
      Preconditions.checkArgument(scale >= 0, "Scale %s cannot be negative", scale);
      Preconditions.checkArgument(
          scale <= precision, "Scale %s cannot be less than precision %s", scale, precision);
    }
  }

  static {
    LogicalTypes.register(
        ParquetDecimal.NAME,
        schema -> {
          int precision = Integer.parseInt(schema.getProp("precision"));
          int scale = Integer.parseInt(schema.getProp("scale"));
          return new ParquetDecimal(precision, scale);
        });
  }

  private static class IntDecimalConversion extends Conversion<BigDecimal> {

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