[AVRO-2164] Make Decimal a first class type.

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.8.2
• Component/s: logical types
• Assignee: Unassigned
• Reporter: Andy Coates
• Created: 23/Mar/18 13:13
• Updated: 29/Dec/18 13:30

Description

I'd be interested to hear the communities thoughts on making decimal a first class type. 

The current logical type encodes a decimal into a bytes or fixed. This encoding does not include any information about the scale, i.e. this encoding is lossy. 

There are open issues around the compatibility / evolvability of schemas containing decimal logical types, (e.g. AVRO-2078 & AVRO-1721), that mean reading data that was previously written with a different scale will result in data corruption.

If these issues were fixed, with suitable compatibility checks put in place, this would then make it impossible to evolve an Avro schema where the scale needs to be changed. This inability to evolve the scale is very restrictive, and can result in high overhead for organizations that need to change the scale, i.e. they may potentially need to copy their entire data set, deserializing with the old scale and re-serializing with the new.

If decimal were promoted to a first class type, this would allow the scale to be captured in the serialized form, allow for schema evolution support.

Issue Links

• is related to: AVRO-2078 Avro does not enforce schema resolution rules for Decimal type
• is related to: AVRO-1721 Should LogicalTypes introduce schema (in)compatibility and canonical parsing form changes?