How does a query planner work in PostgreSQL?
Enables or disables the query planner’s ability to eliminate a partitioned table’s partitions from query plans. This also controls the planner’s ability to generate query plans which allow the query executor to remove (ignore) partitions during query execution. The default is on.
Why is partitionwise join planning off in PostgreSQL?
Because partitionwise join planning can use significantly more CPU time and memory during planning, the default is off. Enables or disables the query planner’s use of partitionwise grouping or aggregation, which allows grouping or aggregation on a partitioned tables performed separately for each partition.
What’s the default for parallel scanning in PostgreSQL?
The default is 0.1. Sets the minimum amount of table data that must be scanned in order for a parallel scan to be considered. For a parallel sequential scan, the amount of table data scanned is always equal to the size of the table, but when indexes are used the amount of table data scanned will normally be less.
What do I need to know about query planning?
Enables or disables the query planner’s use of bitmap-scan plan types. The default is on. Enables or disables the query planner’s use of gather merge plan types. The default is on. Enables or disables the query planner’s use of hashed aggregation plan types. The default is on. Enables or disables the query planner’s use of hash-join plan types.
How are cost variables set in PostgreSQL query planning?
Only their relative values matter, hence scaling them all up or down by the same factor will result in no change in the planner’s choices. By default, these cost variables are based on the cost of sequential page fetches; that is, seq_page_cost is conventionally set to 1.0 and the other cost variables are set with reference to that.