[jira] [Created] (SPARK-38591) Add flatMapSortedGroups to KeyValueGroupedDataset

["Enrico Minack (Jira)" <ji...@apache.org>]

Enrico Minack created SPARK-38591:
-------------------------------------

             Summary:  Add flatMapSortedGroups to KeyValueGroupedDataset
                 Key: SPARK-38591
                 URL: https://issues.apache.org/jira/browse/SPARK-38591
             Project: Spark
          Issue Type: New Feature
          Components: SQL
    Affects Versions: 3.3.0
            Reporter: Enrico Minack


The existing method {{KeyValueGroupedDataset.flatMapGroups}} provides an iterator of rows for each group key. If user code would requires those rows in a particular order, that iterator would have to be sorted first, which is against the idea of an iterator in the first place. For groups that do not fit into memory of one executor, this approach does not work.

[org.apache.spark.sql.KeyValueGroupedDataset|https://github.com/apache/spark/blob/47485a3c2df3201c838b939e82d5b26332e2d858/sql/core/src/main/scala/org/apache/spark/sql/KeyValueGroupedDataset.scala#L134-L137]:
{noformat}
Internally, the implementation will spill to disk if any given group is too large to fit into
memory. However, users must take care to avoid materializing the whole iterator for a group
(for example, by calling `toList`) unless they are sure that this is possible given the memory
constraints of their cluster.
{noformat}


The implementation of {{KeyValueGroupedDataset.flatMapGroups}} already sorts each partition according to the group key. By additionally sorting by some data columns, the iterator can be guaranteed to provide some order.

A new method {{KeyValueGroupedDataset.flatMapSortedGroups}} could allow to define order within the groups.



--
This message was sent by Atlassian Jira
(v8.20.1#820001)

---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscribe@spark.apache.org
For additional commands, e-mail: issues-help@spark.apache.org