How much memory of Memcache is available to a Google App Engine account?

Question

Google App Engine has some information about Memcache limits:

• http://code.google.com/appengine/docs/quotas.html#Memcache
• http://code.google.com/appengine/docs/python/memcache/overview.html#Quotas_and_Limits

However, total allowed size of RAM/memory store for a single application is not specified. It's known that no objects above 1MB is allowed. Do you have information?

Parallelism

Answer 1

The amount of memcache capacity your app has isn't fixed, and may vary depending on the traffic to your app and how it uses memcache.

Bolide

Nick, are there any plans to publish some sort of general guidelines or rules of thumb for understanding or predicting memcache behavior? It feels difficult to intelligently use memcache to get optimal performance when I would like to put absolutely everything in there, but I don't want to accidentally evict some things that I really, really need for the sake of something that might be less important. Is there some generally-applicable algorithm for making that decision? – Lumpkin

In broad terms: Trust the eviction policy. Put everything in there that could be useful, and the stuff that gets accessed the most will stay there longest. – Bolide

@NickJohnson - that's all very well, but what if I know item A costs me USD1 per thousand to recreate and item B costs USD0.10? – Sadiron

In a recent youtube video n the google developers channel, they even said that you should choose carefully what you put in memcache. youtube.com/watch?v=TGl81wr8lz8 Although this might be guided towards apps with a very large amount of data, where any place in your app that adds to memcache adds a huge amount of data. youtube.com/watch?v=TGl81wr8lz8 – Repairman

This answer only applies to the default free shared memcache. See other answer from mndrix for information about how to buy your own dedicated memcache space. – Supat

@EamonnO'Brien-Strain This answer was written long before paid memcache. Feel free to update it! – Bolide

Answer 2

As of November 2013, App Engine offers dedicated memcache which guarantees a specific amount of memcache RAM. You can purchase between 1 and 20 GB of dedicated cache. More than 20 GB is available upon request.

The shared memcache RAM available to an application still varies based on multiple factors.

Superlative