Php Globals v. Database calls for lots of data

Question

For large arrays, is it better to save the data to global variables or query the database each time I need them? In my situation keeping them local scope and passing them to functions isn't an option.

I'm using wordpress and in most pages I get every user and all metadata attached to them. Often times I use these variables in multiple places on the same page. Unfortunately wordpress won't let me pass variables between templates so I'm stuck either using global variables or calling the database each time. Eventually, this will be hundreds of users with a lot of metadata attached to each. Should I call the database each time to keep the variables local, or should save them to global variables to save on database queries? What are the considerations? Should I worry about performance, overhead, and/or other issues?

Thanks so much!

Answer 1

The only real solution to your problem is using some kind of cache system ( Memcache and Redis are your best options). Fortunately, there are plenty of Wordpress plugins that make the integration an easy thing. For instance:

• Redis: https://wordpress.org/plugins/redis-object-cache/
• Memcache: https://wordpress.org/plugins/memcached/

EDIT

If you only want to cache a few databases calls, you can forget about Wordpress plugins and start coding a bit. Let's say you only want to cache the call for retrieving the list of users from database, and let's assume you are using Memcache to accomplish this task (Memcache stores key-value pairs and allows super fast access to a value given a key).

1. Query Memcache asking for the key " users ".
2. Memcache still doesn't have such key, so you'll have a cache fail and after it, you'll query your database to retrieve the user list. Now serialize the database response ( serialize and json_encode are two different ways to do this) and store the key " users " along this serialized value in your memcache.
3. Next time you query your memcache asking for "users", you'll get a hit. In this moment you just have to unserialize the value and work with your user list.

And that's all. Now you just have to decide what you want to cache and apply this procedure to those elements.

Answer 2

You shouldn't have to perform the calls but once per page, you might have to execute the call once for every page. So I would suggest you creating some sort of class to interact with your database that you can call on to get the data that you need. I would also recommend using stored procedures and functions on your database instead of straight queries since this will help both with security and separation of application logic and data functionality.