Understanding caching

Question

Synopsis

I've noticed constantly throughout forum threads, blog articles and Q&A many problems are caused through caching not being cleared.

I think I understand the basics with caching and indexing but i'm hoping someone with extensive knowledge could potentially clear this up for me.

I am not asking for information about NginX or Varnish and the likes, but specifically how Magento caches and indexes content.

There are times when I have physically removed the var/cache directory and let Magento rebuild it and things started to work.

Cache Management

Within the Admin Console under System > Configuration > Cache Management we have:

• Flush Magento Cache;
• Flush Cache Storage;

Can someone explain to me what caching pools are flushed by the above buttons?

Within the grid there are several default levels of caching for:

• XML configuration (which i thought was just config.xml files but it seems is layout local.xml files included)
• Layout XML: why is local.xml not cached here?
• Collections data: exactly what is it that is being cached and where?
• EAV types and attributes: I presume this is to do with associating attributes to catalog_product or customer?

On top of this there is additional caching for CSS/Javascript and Images:

• Flush Catalog Images Cache;
• Flush CSS/JavaScript Cache;

What are the above buttons flushing and how are those caches built?

Additional information

Can anyone explain any further information or link to an article that might help understand in more details how the caching works with Magento?

Answer 1

I think this Link might be very helpful to you if you want to understand magento cache.