Hi Andy, I think the intent of that sentence was to define a schema evolution rule, because it starts with "purposes of schema resolution", though it is not in the proper 'Schema resolution' part of Avro spec. If so, then in my opinion either implementation should enforce this rule (AVRO-2078), or we should delete this sentence from the spec (because it is misleading) and clarify that Avro doesn't enforce any evolution rule for logical types, it is up to the libraries that use Avro to handle reader/writer logical type changes. Thoughts?
Nandor On Fri, Jul 27, 2018 at 3:25 PM, Andy Coates <[email protected]> wrote: > Hi [~nkollar], > > I'd say that's a rule for decimal comparison, not evolution. > > On Fri, 20 Jul 2018 at 13:10, Nandor Kollar (JIRA) <[email protected]> > wrote: > > > > > [ > > https://issues.apache.org/jira/browse/AVRO-2164?page= > com.atlassian.jira.plugin.system.issuetabpanels:comment- > tabpanel&focusedCommentId=16550713#comment-16550713 > > ] > > > > Nandor Kollar commented on AVRO-2164: > > ------------------------------------- > > > > [~BigAndy] I wanted to refer to this in the Decimal section of the spec: > > "For the purposes of schema resolution, two schemas that > > are decimal logical types _match_ if their scales and precisions match." > > This sounds like a rule for schema evolution, and scale and precision > > should match (the current doesn't check for this). > > > > > Make Decimal a first class type. > > > -------------------------------- > > > > > > Key: AVRO-2164 > > > URL: https://issues.apache.org/jira/browse/AVRO-2164 > > > Project: Avro > > > Issue Type: Improvement > > > Components: logical types > > > Affects Versions: 1.8.2 > > > Reporter: Andy Coates > > > Priority: Major > > > > > > 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. > > > > > > > > -- > > This message was sent by Atlassian JIRA > > (v7.6.3#76005) > > >
