What does it mean to reach a stable point during the execution of a job?

Question

Trying to use sp_stop_job to stop a simple job that inserts data on a table when 100 rows were inserted I got confused to see the table end up with more than 100 rows every time. Under the Remarks section of the sp_stop_job doc it says:

sp_stop_job sends a stop signal to the database. Some processes can be stopped immediately and some must reach a stable point (or an entry point to the code path) before they can stop.

I don't understand what it means to reach a stable point (or an entry point to the code path) and I believe the job keeps inserting the data on the table because it is still reaching that stable point.

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The code:

CREATE TABLE [dbo].[myStopJobTable](
    [id] [int] NULL,
    [nome] [varchar](50) NULL
);

I created a job with a step to execute the following code:

WHILE (1=1)
BEGIN  

    INSERT INTO MyLab.dbo.myStopJobTable
    VALUES (1, 'Some Name');

    IF ((SELECT COUNT(*) FROM myStopJobTable) = 100)
    BEGIN
        EXEC msdb.dbo.sp_stop_job N'JobToBeStopped';
    END

END;

From that sample code I expected the job to stop before the row 101 is inserted, but it doesn't. By adding a BREAK inside the IF block the process is stopped before the insertion of row 101 happens, but in that case it's not the sp_stop_job working.

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I don't want a fix for the job, what I seek is to understand that stable point (or an entry point to the code path). What does it mean?

Answer 1

The job is not waiting to "reach a stable point". The key point is:

sp_stop_job sends a stop signal to the database.

sp_stop_job sends the stop request SQL Server Agent but does not wait for it to complete. The T-SQL script continues while SQL Server Agent processes the stop request asynchronously. The additional rows inserted after sp_stop_job was executed reflect the time between receipt of the stop request until SQL Server Agent got around to cancelling it. This typically takes a few milliseconds or more depending on overall activity.

The note about "reach a stable point" in the context of a T-SQL job step is the same as any query cancel request. It includes the time the database engine needs to release resources and rollback the transaction. That time is insignificant with the singleton insert in your example but would be more noticeable had the cancelled script done more work, like inserted millions of rows in a single transaction.