How to create a transient that persists the data for the whole duration of the expiration, even when object cache is enabled?

Question

Anyone recommends an alternative to set_transient that persists the data for the whole duration of the expiration even when object cache is enabled?

Example:

• List item
• Set a long-duration transient set_transient('foo', 'bar', WEEK_IN_SECONDS);
• Site is using object cache, so this is saved in memory
• I don't know internals of Redis, but memory cache is cleared for some reason:
  • Redis rotates cache based on the eviction policy
  • Server reboots
  • O.S-level memory management frees up memory
  • etc?

Now that transient expired before 1 week.

In a scenario such as this, how can I create a value that is able to persist for a longer period?

Answer 1

I eventually used a combination of update_option and WP Cron:

// Create the option.
update_option('foo', 'bar', false);

/**
* Schedule it to be deleted one week from now.
* 
* @param int Expiration timestamp
* @param string Hook that will be invoked
* @param string Params to send to the hook callback
*/
wp_schedule_single_event( time() + WEEK_IN_SECONDS, 'expire_option', [ 'foo' ] );

// Register the hook.
add_action( 'expire_option', 'expire_option_callback', 10, 1 );

// This will be called by WP Cron when we want to "expire" the option, one week after its creation.
function expire_option_callback( $option_name ) {
  delete_option( $option_name );
}

The only drawback is that the option won't be expired if WP Cron is not working in the site. If this is unnaceptable, you'll need a more robust solution mimicking how transients are saved and expired in the DB.