[AVRO-2099] Decimal precision is ignored

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: spec
• Assignee: Unassigned
• Reporter: Kornel Kiełczewski
• Created: 24/Oct/17 07:57
• Updated: 30/Dec/18 05:41

Description

According to the documentation https://avro.apache.org/docs/1.8.1/spec.html#Decimal

The decimal logical type represents an arbitrary-precision signed decimal number of the form unscaled × 10-scale.

Then in the schema we might have an entry like:

{
  "type": "bytes",
  "logicalType": "decimal",
  "precision": 4,
  "scale": 2
}

However, in the java deserialization I see that the precision is ignored:

https://github.com/apache/avro/blob/master/lang/java/avro/src/main/java/org/apache/avro/Conversions.java#L79

    @Override
    public BigDecimal fromBytes(ByteBuffer value, Schema schema, LogicalType type) {
      int scale = ((LogicalTypes.Decimal) type).getScale();
      // always copy the bytes out because BigInteger has no offset/length ctor
      byte[] bytes = new byte[value.remaining()];
      value.get(bytes);
      return new BigDecimal(new BigInteger(bytes), scale);
    }

The logical type definition in the java api requires the precision to be set:

https://github.com/apache/avro/blob/master/lang/java/avro/src/main/java/org/apache/avro/LogicalTypes.java#L116

  /** Create a Decimal LogicalType with the given precision and scale */
  public static Decimal decimal(int precision, int scale) {
    return new Decimal(precision, scale);
  }

Is this a feature, that we allow arbitrary precision? If so, why do we have the precision in the API and schema, if it's ignored?

Maybe that's some java specific issue?

Thanks for any hints.