apache/iceberg · error · java.lang.UnsupportedOperationException

Unsupported base type for decimal

Error message

Unsupported base type for decimal: ${desc.getPrimitiveType().getPrimitiveTypeName()}

What it means

Iceberg's Flink Parquet writer visits a Parquet column of logical decimal type and chooses a writer based on the underlying physical Parquet type (INT32, INT64, BINARY, FIXED_LEN_BYTE_ARRAY). If the physical type is none of those, no decimal writer exists and the library throws this UnsupportedOperationException. This indicates malformed or unsupported Parquet schema rather than bad user data.

Solutions

1. Check the Parquet file's schema with parquet-tools and fix the physical type to INT32, INT64, BINARY, or FIXED_LEN_BYTE_ARRAY for the decimal column
2. Regenerate the file with a standards-compliant writer (Spark/Iceberg)
3. If this is a legitimately new physical encoding, extend FlinkParquetWriters.decimal switch to support it and file an upstream issue

Example fix

// before: file written with nonstandard physical type FLOAT + decimal annotation
// after: rewrite the table so decimals use a valid physical type
spark.sql("CREATE TABLE fixed STORED BY iceberg AS SELECT CAST(dec_col AS DECIMAL(20,6)) FROM bad")

org.apache.parquet.schema.PrimitiveType pt = desc.getPrimitiveType();
if (!(pt.getPrimitiveTypeName() == PrimitiveTypeName.INT32 || pt.getPrimitiveTypeName() == PrimitiveTypeName.INT64 || pt.getPrimitiveTypeName() == PrimitiveTypeName.BINARY || pt.getPrimitiveTypeName() == PrimitiveTypeName.FIXED_LEN_BYTE_ARRAY)) {
  throw new IllegalArgumentException("Column " + desc + " has invalid physical type for decimal: " + pt.getPrimitiveTypeName());
}

try { writer = FlinkParquetWriters.buildWriter(...); } catch (UnsupportedOperationException e) { if (e.getMessage().startsWith("Unsupported base type for decimal")) { /* repair schema or reroute */ } else throw e; }

When it happens

Trigger: Writing decimal data through FlinkParquetWriters when the Parquet ColumnDescriptor's physical primitive type is not INT32/INT64/BINARY/FIXED_LEN_BYTE_ARRAY (e.g. FLOAT/DOUBLE or BOOLEAN physical type carrying a decimal logical annotation), typically from corrupt or non-standard Parquet files.

Common situations: Reading/writing Parquet files produced by third-party tools that attach a decimal logical type to an unexpected physical type; corrupted schema metadata; manually crafted Parquet schemas.

Related errors

• Unsupported base type for decimal
• Unsupported base type for decimal:
• Unsupported base type for decimal:
• Unsupported base type for decimal:
• Unsupported base type for decimal

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/5924bc3e0602132d. Report an issue: GitHub.

Appendix: source

Thrown at flink/v2.1/flink/src/main/java/org/apache/iceberg/flink/data/FlinkParquetWriters.java:253

      return Optional.of(strings(desc));
    }

    @Override
    public Optional<ParquetValueWriter<?>> visit(DecimalLogicalTypeAnnotation decimal) {
      ParquetValueWriter<DecimalData> writer;
      switch (desc.getPrimitiveType().getPrimitiveTypeName()) {
        case INT32:
          writer = decimalAsInteger(desc, decimal.getPrecision(), decimal.getScale());
          break;
        case INT64:
          writer = decimalAsLong(desc, decimal.getPrecision(), decimal.getScale());
          break;
        case BINARY:
        case FIXED_LEN_BYTE_ARRAY:
          writer = decimalAsFixed(desc, decimal.getPrecision(), decimal.getScale());
          break;
        default:
          throw new UnsupportedOperationException(
              "Unsupported base type for decimal: "
                  + desc.getPrimitiveType().getPrimitiveTypeName());
      }
      return Optional.of(writer);
    }

    @Override
    public Optional<ParquetValueWriter<?>> visit(DateLogicalTypeAnnotation dates) {
      return Optional.of(ints(flinkType, desc));
    }

    @Override
    public Optional<ParquetValueWriter<?>> visit(TimeLogicalTypeAnnotation times) {
      Preconditions.checkArgument(
          LogicalTypeAnnotation.TimeUnit.MICROS.equals(times.getUnit()),
          "Cannot write time in %s, only MICROS is supported",
          times.getUnit());
      return Optional.of(timeMicros(desc));

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