Oracle AI 26ai

The other day I saw that besides the catcon.pl, there is a catcon_kill_sess_gen.sql:

ls -1 $ORACLE_HOME/rdbms/admin/catcon*
/u00/app/oracle/product/19.30.0/rdbms/admin/catcon_kill_sess_gen.sql
/u00/app/oracle/product/19.30.0/rdbms/admin/catcon.pl
/u00/app/oracle/product/19.30.0/rdbms/admin/catcon.pm
/u00/app/oracle/product/19.30.0/rdbms/admin/catconst.pm
/u00/app/oracle/product/19.30.0/rdbms/admin/catcont.sql

When looking at this file, I noticed it kills catcon session using a “ALTER SYSTEM KILL SESSION ‘sid, serial#’ FORCE TIMEOUT 0”, except if on Oracle 12.1, where still does “IMMEDIATE” instead:

This new syntax “FORCE TIMEOUT x” is first described in Oracle AI 26ai DB documentation (but it seems to work from version 12.2). Basically it theoretically allows the draining of sessions by setting a timeout until the session terminates some task, before killing it.

There are two new elements here: “FORCE” and “TIMEOUT x”.

What I understood from documentation is:

When not using the “FORCE” keyword, the two following commands behave the same way:

ALTER SYSTEM KILL SESSION ‘sid, serial#’ IMMEDIATE = ALTER SYSTEM KILL SESSION ‘sid, serial#’ TIMEOUT 0

Basically, it instructs Oracle to terminate a session and roll back ongoing transactions, release all session locks, recover the entire session state, and return control to you immediately.

With the “FORCE” keyword alone, it terminates the session like “IMMEDIATE”, however waiting first for a timeout of 5 seconds.

With the “FORCE TIMEOUT 0”, then the connection is closed immediately, when there is some activity going on.

Here a summary of what I observed:

Just for completion, if using “DISCONNECT SESSION” instead, then the session might just automatically failover if the parameters are correctly set.

Le me know if you have other inputs.

While reading the very interesting Oracle AI Database 26ai New Features Guide, I got to know that there is a new “QUALIFY” filter clause (there is also a new “FILTER” clause). However, what I found more interesting in the documentation was this sentence:

The order of operations is as follows: FROM → WHERE → GROUP BY → HAVING → WINDOW → QUALIFY → DISTINCT → ORDER BY → FETCH FIRST.

This is somehow a back to the roots and basic SQL information that I had in the back of my head, but never though really end-to-end about.

Here an example of query using all except DISTINCT elements of the operations order:

SELECT region, city, AVG(temperature), AVG(AVG(temperature)) OVER w AS avg_temp_region 
    FROM city, regions 
    WHERE city.region_id = region.region_id 
    GROUP BY region, city 
    HAVING region NOT LIKE 'LISBON' 
    WINDOW w AS (PARTITION BY region)
    QUALIFY avg_temp_region > 10
    ORDER BY region
    FETCH FIRST 5 ROWS ONLY;

I don’t think I could write a SQL like that, but at least now I know how it looks like.