Module development and code questions

Hello.

I've created a custom handler for an autocomplete textfield, in a form. this is the code :

Hello,

Is there #ajax working for Drupa 8? I wanted to do custom plugin, add simple reload of table, but it is not called.

Using in buildForm function:

We are running the latest version of Drupal (8.6.3) and trying to sort out the page layouts. We have the next recurrence showing in the views which is good but we need to alter the twig.html file to show the next meeting date

We currently have this which shows a single date from the old layout 

            <div class="next_event-date">
              <div class="month">{{ event_start_date_month }}</div>
              <div class="day">{{ event_start_date_day }}</div>
            </div>

What are store procedures? How to use it with Drupal 8?

Is there any step by step document available to improve Drupal 8 website performance?

Hi,

What are slow query logs? How do we analyse these logs to improve site performance?