Appengine: Why dedicated memcache keeps resetting?

Question

I am using GAE 1 gb dedicated memcache. 1 gm size is more than enough for my application's use.

The memcache reset behavior is strange.

Normally I see the following values:

• Hit ratio 88.68%
• Oldest item age 2 days
• Total cache size to 800 MB

and then of sudden it resets to the following:

• Oldest item age 5 minutes
• Total cache size 20 MB

I am worried why this get reset?

Any info/help will be appreciated.

Answer 1

There are two possible explanations for this behavior I can think of.

1. There's maintenance going on in the Google data center, where your app resides. In which case Google may decide to evict your values.

   Whether shared or dedicated, memcache is not durable storage. Keys may be evicted when the cache fills up, according to the cache's LRU policy. Changes in the cache configuration or datacenter maintenance events may also flush some or all of the cache. (Source)

2. It could be the app code itself. Since you can set a maximum lifetime of a cache value, it can happen that lots of values decay at the same time. That is especially the case when you have tasks that load many values into memcache once in a while.

If you can exclude (2) and the behavior is reproducable (or evicts happen just way to often to be explained by maintenance) you may want to contact the Google support and ask what's going on with your paid service.