zhuqi-lucas commented on code in PR #16216: URL: https://github.com/apache/datafusion/pull/16216#discussion_r2116036299
########## docs/source/library-user-guide/upgrading.md: ########## @@ -21,6 +21,55 @@ ## DataFusion `48.0.0` +### `VARCHAR` SQL type changed to map to `Utf8View` Arrow type + +The mapping of the SQL `VARCHAR` type has been changed from `Utf8` to `Utf8View` +which improves performance for many string operations. You can read more about +`Utf8View` in the [DataFusion blog post on German-style strings] + +[datafusion blog post on german-style strings]: https://datafusion.apache.org/blog/2024/09/13/string-view-german-style-strings-part-1/ + +This means that when you create a table with a `VARCHAR` column, it will now use +`Utf8View` as the underlying data type. For example: + +```sql +> CREATE TABLE my_table (my_column VARCHAR); +0 row(s) fetched. +Elapsed 0.001 seconds. + +> DESCRIBE my_table; ++-------------+-----------+-------------+ +| column_name | data_type | is_nullable | ++-------------+-----------+-------------+ +| my_column | Utf8View | YES | ++-------------+-----------+-------------+ +1 row(s) fetched. +Elapsed 0.000 seconds. +``` + +You can restore the old behavior of using `Utf8` by changing the +`datafusion.sql_parser.map_varchar_to_utf8view` configuration setting. For +example + +```sql +> set datafusion.sql_parser.map_varchar_to_utf8view = false; +0 row(s) fetched. +Elapsed 0.001 seconds. + +> CREATE TABLE my_table (my_column VARCHAR); +0 row(s) fetched. +Elapsed 0.014 seconds. + +> DESCRIBE my_table; ++-------------+-----------+-------------+ +| column_name | data_type | is_nullable | ++-------------+-----------+-------------+ +| my_column | Utf8 | YES | ++-------------+-----------+-------------+ +1 row(s) fetched. +Elapsed 0.004 seconds. +``` + Review Comment: Thank you @alamb , i think we also need to add note: If customers use avro format, for datafusion 48.0, we need to set datafusion.sql_parser.map_varchar_to_utf8view = false; Because the support for utf8view for avro are not releasing currently. https://github.com/apache/arrow-rs/issues/7262 -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For additional commands, e-mail: github-h...@datafusion.apache.org
