apache/iceberg · error · java.lang.UnsupportedOperationException

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

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.

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));

View on GitHub (pinned to 86d9c8fc54)

Solutions

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
Regenerate the file with a standards-compliant writer (Spark/Iceberg)
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")

Defensive patterns

Strategy: validation

Validate before calling

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 / catch

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

Prevention

Inspect Parquet schema with parquet-tools before ingesting third-party files
Only write decimals with Spark/Iceberg-compliant writers
Validate physical/logical type pairs in a schema check step

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

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