optimizer_dynamic_sampling

Description

optimizer_dynamic_sampling specifies the level of dynamic sampling.

Privilege requirements

• Query variables

  • Global level

    sys tenant and all user tenants can execute the SHOW VARIABLES statement or query the SYS.TENANT_VIRTUAL_GLOBAL_VARIABLE view (Oracle-compatible mode) or the information_schema.GLOBAL_VARIABLES view (MySQL-compatible mode) to obtain the value of a global system variable.

  • Session level

    sys tenant and all user tenants can execute the SHOW VARIABLES statement or query the SYS.TENANT_VIRTUAL_SESSION_VARIABLE view (Oracle-compatible mode) or the information_schema.SESSION_VARIABLES view (MySQL-compatible mode) to obtain the value of a session system variable.

• Modify variables

  • Global level

    • sys tenant can directly modify the value of a global system variable.

    • MySQL user tenant must have the SUPER or ALTER SYSTEM privilege to modify the value of a global system variable.

    • Oracle user tenant must have the ALTER SYSTEM privilege to modify the value of a global system variable.

  • Session level

    sys tenant and all user tenants can directly modify the value of a session system variable.

Attributes

Examples

Set the level of dynamic sampling to 1.

• Global level

  obclient> SET GLOBAL optimizer_dynamic_sampling=1;
  

• Session level

  obclient> SET optimizer_dynamic_sampling=1;
  

References

Dynamic sampling