What is "cold storage" in the context of larger MMOs?

Question

What is a cold storage and what is it used for? I'm not sure if I should use cold storage in my game. I heard it can be used for chat logs, however I'd rather someone here answer all my questions.

Answer 1

The "temperature" of different data storage layers usually refers to how fast that data can be accessed. Different levels of "temperature" from hottest to coldest are:

• In the gameserver's memory
• In an in-memory database or in-memory caching layer
• In a ssd-backed database
• In a hdd-backed database
• In a flatfile
• In a compressed flatfile
• Offsite Backup

Note that these are just examples. Not every game will use exactly these tiers of data storage. There might also be sub-layers like indexed vs. non-indexed and denormalized vs. normalized data structures.

When you have data which you need to access very frequently, like the data of characters which are currently on-line, you would want to move them to a "hotter" storage layer. When you have data which you need to access very rarely, you will want to move them to a "colder" layer.

Old chatlogs are data which you usually archive just in case you need to investigate some reported TOS violation at a later date. Most of your chatlogs won't be accessed ever, and in those cases where you do need to access them, performance isn't very important. So they are a usually a candidate for colder storage layers (if you want to archive them at all).