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Posted to issues@spark.apache.org by "Erik Krogen (Jira)" <ji...@apache.org> on 2021/02/04 18:59:00 UTC
[jira] [Commented] (SPARK-34365) Support configurable Avro schema
field matching for positional or by-name
[ https://issues.apache.org/jira/browse/SPARK-34365?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17279073#comment-17279073 ]
Erik Krogen commented on SPARK-34365:
-------------------------------------
I plan to post a PR for this in the next few days, unless I hear pushback that this is a bad idea.
> Support configurable Avro schema field matching for positional or by-name
> -------------------------------------------------------------------------
>
> Key: SPARK-34365
> URL: https://issues.apache.org/jira/browse/SPARK-34365
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.0.1
> Reporter: Erik Krogen
> Priority: Major
>
> When reading an Avro dataset (using the dataset's schema or by overriding it with 'avroSchema') or writing an Avro dataset with a provided schema by 'avroSchema', currently the matching of Catalyst-to-Avro fields is done by field name.
> This behavior is somewhat recent; prior to SPARK-27762 (fixed in 3.0.0), at least on the write path, we would match the schemas by positionally ("structural" comparison). While I agree that this is much more sensible for default behavior, I propose that we make this behavior configurable using an {{option}} for the Avro datasource.
> There is precedence for configurability of this behavior as seen in SPARK-32864, which added this support for ORC. Besides this precedence, the behavior of Hive is to perform matching positionally ([ref|https://cwiki.apache.org/confluence/display/Hive/AvroSerDe#AvroSerDe-WritingtablestoAvrofiles]), so this is behavior that Hadoop/Hive ecosystem users are familiar with:
> {quote}
> Hive is very forgiving about types: it will attempt to store whatever value matches the provided column in the equivalent column position in the new table. No matching is done on column names, for instance.
> {quote}
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