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From "Scott Carey (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AVRO-816) Schema Comparison Utils
Date Thu, 07 Jul 2011 20:08:17 GMT

    [ https://issues.apache.org/jira/browse/AVRO-816?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13061552#comment-13061552
] 

Scott Carey commented on AVRO-816:
----------------------------------

{code}
return getFixedSize() >= other.getFixedSize();
{code}

I believe the below is incorrect for a fixed schema subsuming another.  You cannot type promote
a fixed schema from one length to a longer one.  The spec states that the sizes must match.

> Schema Comparison Utils
> -----------------------
>
>                 Key: AVRO-816
>                 URL: https://issues.apache.org/jira/browse/AVRO-816
>             Project: Avro
>          Issue Type: New Feature
>          Components: java
>            Reporter: Joe Crobak
>            Assignee: Joe Crobak
>            Priority: Minor
>         Attachments: AVRO-816.patch, AVRO-816.patch, AVRO-816.patch
>
>
> From my post on the mailing list, and Doug's response:
> {quote}
> On 05/05/2011 10:29 AM, Joe Crobak wrote:
> > We've recently come across a situation where we have two data files with
> > different schemas that we'd like to process together using
> > GenericDatumReader.  One schema is promotable to the other, but not vice
> > versa.  We'd like to programmatically determine which of the schemas to
> > use.  I did a brief look through javadoc and tests, and I couldn't find
> > any examples of checking if one schema is promotable to the other.  Has
> > anyone else come across this?
> >
> > For some context, we're considering patching AvroStorage [1] to remove
> > the assumption that all files have the same schema.  In our case, our
> > schema has evolved in that a field that was an int was promoted to a long.
> A boolean method that tells you if one schema is promotable to another
> would work in this case, but would not help in cases where, e.g.,
> different fields had changed in different versions.  For example, in
> branched development, two branches might each add a distinct symbol to
> an enum.  So I think you might be better off with a method that, given
> two schemas, returns their superset, a schema that can read data written
> by either.
> Such a method does not yet exist in Avro, but should not be difficult to
> add.  Please file an issue in Jira if this sounds of interest.
> Doug
> {quote}
> I think it would be useful to have both of the methods that Doug mentioned in some sort
of schema utils class.

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