What are the size limits for Laravel's file-based caching?

Question

I am a new developer and am trying to implement Laravel's (5.1) caching facility to improve the speed of my app. I started out caching a large DB table that my app constantly references - but it got too large so I have backed away from that and am now 'forever' caching smaller chunks of data - for example, for each page only the portions of that large DB table that are relevant.

I have watched 'Caching Essentials' on Laracasts, done some Googling and had a search in this forum (and Laracasts') but I still have a couple of questions:

1. I am not totally clear on how the cache size limits work when you are using Laravel's file-based system - is there an overall in-app size limit for the cache or is one limited size-wise only per key and by your server size?

2. What are the signs you should switch from file-based caching to something like Memcached or Redis - and what are the benefits of using one of those services? Is it the fact that your caching is handled on a different server (thereby lightening the load on your own)? Do you switch over to one of these services when your local, file-based cache gets too big for your server?

My app utilizes several tables that have 3,000-4,000 rows - the data in these tables is constantly referenced and will remain static unless I decide to add new options. I am basically looking for the best way to speed up queries to the data in these tables.

Thanks!

Answer 1

1. I don't think Laravel imposes any limitations on its file i/o at all - the limitations will be with how much what PHP can read / write to a file at once, or hold in its memory / process at any one time.
   It does serialise the data that you cache, and unserialise it when you reload it, so your PHP environment would have to be able to process the entire cache file (which is equivalent to the top level cache key) at once. So, if you are getting cacheduser.firstname, it would have to load the whole cacheduser key from the file, unserialise it, then get the firstname key from that.
   I would take the PHP memory limit (classic, i know!) as a first point to investigate if you want to keep down this road.

2. Caching services like Redis or memcached are bespoke, optimised caching solutions. They take some of the logic and responsibility out of your PHP environment.
   They can, for example, retrieve sub-keys from items without having to process the whole thing, so can retrieve part of some cached data in a memory efficient way. So, when you request cacheduser.firstname from redis, it just returns you the firstname attribute.
   They have other advantages regarding tagging / clearing out subsets of caches (see [the cache tags Laravel docs] (https://laravel.com/docs/5.4/cache#cache-tags))
   Another thing to think about is scaling. If your site is large enough, and is load-balanced across multiple servers, the filesystem caching may be different across those servers, as each server can only check their local filesystem for the cache files. A caching service can be on a different server (many hosts will have a separate redis / memcached services available), so isn't victim to this issue.
   Also - as I understand it (and this might be the most important thing), the file cache driver in Laravel is mainly for local development and testing. Although it can work fine for simple applications with basic caching needs, it's not intended for large scalable production environments.

Personally, I develop locally and test with file caching, as i'm only dealing with small amounts of data then, and use redis to cache on production environments.

It doesn't necessarily need to be on a separate server to get the benefits. If you are never going to scale to multiple application servers, then using a caching service on the same server will already be a large improvement to caching large documents.