ob_udf_selectivity

Overview

ob_udf_selectivity is used to set the selectivity of a UDF predicate.

Privilege requirements

• Query variables

  • Global level

    The sys tenant and all user tenants can use the SHOW VARIABLES statement, or the SYS.TENANT_VIRTUAL_GLOBAL_VARIABLE view (in Oracle-compatible mode) and the information_schema.GLOBAL_VARIABLES view (in MySQL-compatible mode), to view the values of global system variables.

  • Session level

    The SHOW VARIABLES statement, or the SYS.TENANT_VIRTUAL_SESSION_VARIABLE view (in Oracle-compatible mode) and the information_schema.SESSION_VARIABLES view (in MySQL-compatible mode), can be used by the sys tenant and all user tenants to view the values of session system variables.

• Modify variables

  • Global effective

    • The sys tenant can directly modify the values of global system variables.

    • MySQL user tenants must have the SUPER or ALTER SYSTEM privilege to modify the values of global system variables.

    • Oracle user tenants must have the ALTER SYSTEM privilege to modify the values of global system variables.

  • Session expiration

    The sys tenant and all user tenants can directly modify the values of session system variables for their own tenants.

Attributes

Usage instructions

You can configure the selectivity based on the actual filtering conditions of the UDF predicate. Generally, the default value of 0.005 is sufficient.

Configuration example

Configure the selectivity of the UDF predicate to 0.999.

• Effective globally

  obclient> SET GLOBAL ob_udf_selectivity = 0.999;
  

• Session Validity Period

  obclient> SET ob_udf_selectivity = 0.999;