Oracle ALTER SESSION tips

Expert Oracle Database Tips by Donald BurlesonDecember 15, 2015

Question: : What is the Oracle ALTER SESSION statement? I know that ALTER SESSION can change Oracle parameters, but can you change any parameter with an ALTER SESSION statement?

Answer: The ALTER SESSION statement can be embedded anywhere that you issue SQL like SQL*Plus, PL/SQL, or a program with embedded SQL.

Not all parameters can be modified with an ALTER SESSION statement, but you can check to see if a statement is alterable by looking at the v$parameter view.

You can see if any parameter can be changed with an ALTER SESSION statement by looking at the isses_modifiable column in the v$parameter view.

This query will display all parameter that can be changed with an ALTER SESSION statement:

select
    name,
from
    v$parameter
where
    issys_modifiable= 'TRUE';

You can also see if any parameter can be modified with ALTER SESSION or if it is modifiable at the instance level:

select
    name,
    issys_modifiable,
    isinstance_modifiable,
    isses_modifiable
from
    v$parameter
where
    name='nls_date_format';

You may get an error if you specify an ALTER SESSION statement when the parameter only accepts an ALTER SYSTEM statement:

alter session set db_cache_size=200G
*

ERROR at line 1: ORA-02096: specified initialization parameter is not modifiable with this option

Also see these related notes on the ALTER SESSION option.

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