============= Release 0.221

General Changes

• Fix error during stats collection phase of query planning.
• Fix a performance regression for some outer joins without equality predicates when join_distribution_type is set to AUTOMATIC.
• Improve performance for queries that have constant VARCHAR predicates on join columns.
• Add a variant of :func:!strpos that returns the position of the N-th instance of the substring.
• Add :func:!strrpos that returns the position of the N-th instance of a substring from the back of a string.
• Add aggregation function :func:!entropy.
• Add classification aggregation functions :func:!classification_miss_rate, :func:!classification_precision, :func:!classification_recall, :func:!classification_thresholds.
• Add overload of :func:!approx_set which takes in the maximum standard error.
• Add max_tasks_per_stage session property and stage.max-tasks-per-stage config property to limit the number of tasks per stage for grouped execution. Setting this session property allows queries running with grouped execution to use a predictable amount of memory independent of the cluster size.
• Add encryption for spill files (see :doc:/admin/spill).

Web UI Changes

• Add information about query warnings to the web UI.

Raptor Changes

• Revert the change introduced in 0.219 to rebalance bucket assignment after restarting the cluster. Automatic rebalancing can cause unexpected downtime when restarting the cluster to resolve emergent issues.

Hive Connector Changes

• Improve coordinator memory utilization for Hive splits.
• Improve performance of writing large ORC files.

SPI Changes

• Add pageSinkContext for createPageSink in PageSinkProvider and ConnectorPageSinkProvider. It contains a boolean partitionCommitRequired, which is false by default. See the note below about commitPartition for more information.
• Add commitPartition to Metadata and ConnectorMetadata. This SPI is coupled with pageSinkContext#partitionCommitRequired and is used by the engine to commit a partition of data to the target connector. The connector that implements this SPI should ensure that if pageSinkContext#isPartitionCommitRequired is true in ConnectorPageSinkProvider#createPageSink, the written data is not published until ConnectorMetadata#commitPartition is called. Also, it is expected for the connector to add SUPPORTS_PARTITION_COMMIT in Connector#getCapabilities.
• Add ExpressionOptimizer in RowExpressionService. ExpressionOptimizer simplifies a RowExpression and prunes redundant part of it.
• Add pushNegationToLeaves method to LogicalRowExpressions to push negation down below conjunction or disjunction for a logical expression.
• Replace SplitSchedulingStrategy with SplitSchedulingContext in ConnectorSplitManager. SplitSchedulingContext contains the SplitSchedulingStrategy and a boolean schedulerUsesHostAddresses that indicates whether the network topology is used during scheduling. If false, the connector doesn't need to provide the host addresses for remotely accessible splits.