WD_DELETE_METHOD
Option
Specifies the algorithm used during a delete in a WD index.
| Value | Acton |
|---|---|
| 0 | The delete method is selected by the cost model. Cost model only selects either mid or large method for deletion. |
| 1 | Forces small method for deletion. Small method is useful when the number of rows being deleted is a very small percentage of the total number of rows in the table. Small delete can randomly access the index, causing cache thrashing with large datasets. |
| 2 | Forces large method for deletion. This algorithm scans the entire index searching for rows to delete. Large method is useful when the number of rows being deleted is a high percentage of the total number of rows in the table. |
| 3 | Forces mid method for deletion. Mid method is a variation of the small method that accesses the index in order and is generally faster than the small method. |
0
Option can be set at the database (PUBLIC) or user level. At the database level, the value becomes the default for any new user, but has no impact on existing users. At the user level, overrides the PUBLIC value for that user only. No system privilege is required to set option for self. System privilege is required to set at database level or at user level for any user other than self.
Requires the SET ANY PUBLIC OPTION system privilege to set this option. Can be set temporary for an individual connection or for the PUBLIC role. Takes effect immediately.
- Rows deleted
- Index size
- Width of index data type
- Cardinality of index data
- Available temporary cache
- Machine related I/O and CPU characteristics
- Available CPUs and threads
Force the large method for deletion from a WD index:
SET TEMPORARY OPTION WD_DELETE_METHOD = 2