[jira] [Commented] (DRILL-4548) Avro fails on schema changes even when selecting from a single file

["Stefán Baxter (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-4548?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15214926#comment-15214926 ] 

Stefán Baxter commented on DRILL-4548:
--------------------------------------

Ok, this has nothing to do with multiple files either.

Selecting from a single file produces a schema change. (Who would have thunk it)

0: jdbc:drill:zk=local> select type, count(*) from dfs.asa.`/streaming/venuepoint/events/2016-03-28` as s group by type;
Error: UNSUPPORTED_OPERATION ERROR: Hash aggregate does not support schema changes
Fragment 0:0
[Error Id: ad4aa637-e0c5-46fe-b074-814005bf8024 on swift:31010] (state=,code=0)

> Avro fails on schema changes even when selecting from a single file
> -------------------------------------------------------------------
>
>                 Key: DRILL-4548
>                 URL: https://issues.apache.org/jira/browse/DRILL-4548
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Storage - Avro
>    Affects Versions: 1.6.0, 1.7.0
>            Reporter: Stefán Baxter
>
> Hi,
> I have reworked/refactored our Avro based logging system trying to make the whole Drill + Avro->Parquet experience a bit more agreeable.
> Long story short I'm getting this error when selecting form multiple Avro files even though these files share the EXCACT same schema:
> Error: UNSUPPORTED_OPERATION ERROR: Hash aggregate does not support schema changes
> Fragment 0:0
> [Error Id: 00d49aa2-5564-497e-a330-e852d5889beb on swift:31010] (state=,code=0)
> We are using union types but only to allow for null values as seems to be supported by drill as per this comment in the Drill code: 
> // currently supporting only nullable union (optional fields) like ["null", "some-type"].
> This happens for a very simple group_by + count(*) query that only uses two fields in Avro and neither one of them uses a Union construct so and both of them contain string values in every case.
> I now think this has nothing to do with the union types since the query uses only simple string, unless there is a full schema validation done on the content of the files rather then the identical Avro schema embedded in both files.



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