Turns out WP_Background_Process uses an arbitrary value of 20 seconds of wall clock time to measure PHP "time limit" (b0617a13c4/includes/libraries/wp-background-process.php (L385)) instead of cpu time which apparently it is not easy to measure in PHP. Since system calls (like database calls) are not included in the PHP maximum execution time, 20 seconds of wall clock is often way less than PHP time limit.
Thus, this commit removes the call to WP_Background_Process::time_exceeded() while running the function to migrate the post meta _customer_user to the field post_author. If the script times out, WP_Background_Process will restart it.
This change makes it possible to monitor resource usage inside each of the database update functions. Useful when doing resource intensive updates to stop the execution and requeue before the execution is aborted.
Rodrigo Primo
Mike Jolley
Claudio Sanches
Jon Surrell
Shiva Poudel