11.6. Feature Toggles

The default Presto settings should work well for most workloads. The following information may help you if some of the features are not working correctly for you. Though, if you think the behavior of a feature is unexpected, don’t hesitate to file a bug report regardless if it’s enabled or disabled by default.

Config Properties

Name of property	Default value	Description
optimizer.reorder-windows	false	Allow reordering windows in order to put those with the same partitioning next to each other. This may sometimes allow minimizing number of repartitionings.
beta.spill-enabled	false	Try spilling memory to disk to avoid exceeding memory limits for the query. See this section for a more detailed description.

Spilling to disks

Spilling works by offloading memory to disk. This process can allow some queries with large memory footprint to pass at the cost of slower execution times. Currently, spilling is supported only for aggregations, so this property will not reduce memory usage required for joins, window functions and sorting. The spiller can be configured to write simultaneously to multiple directories, which helps to utilize multiple drives installed in the system.

Be aware that this is an experimental feature and should be used with care.

Currently, all queries with aggregations will slow down after enabling spilling. It is recommended to use the spill session property to selectively turn on spilling only for queries that would run out of memory otherwise.

For configuration and session properties, check spilling properties.