New database option WD_DELETE_METHOD [CR 415547]

Sybase IQ 12.7 ESD #3 provides the ability to specify the algorithm used during a delete operation from a WD index using the new database option WD_DELETE_METHOD.

Specifies the algorithm used during a delete in a WD index.

0 – 3

0

DBA permissions are not required to set this option. Can be set temporary, for an individual connection, or for the PUBLIC group. Takes effect immediately.

This option chooses the algorithm used during a delete operation in a WD index. When this option is not set or is set to 0, the delete method is selected by the cost model. The cost model considers the CPU related costs as well as I/O related costs in selecting the appropriate delete algorithm. The cost model takes into account:

• 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

Allowed values for WD_DELETE_METHOD:

• 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.

• 2: Forces large method for deletion. 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 and is generally faster than the small method.

The following statement forces the large method for deletion from a WD index:

SET TEMPORARY OPTION WD_DELETE_METHOD = 2