Re: GAE Dedicated Memcache goes to 0 every day at the same time.

[Mohammad I (Cloud Platform Support)]

By default, the values stored in memcache are retained as long as possible.There are some possible reasons why values can be evicted from Memcache:

The app can provide an expiration time when a value is stored, as either a number of seconds relative to when the value is added, or as an absolute Unix epoch time in the future (a number of seconds from midnight January 1, 1970). The value is evicted no later than this time, though it can be evicted earlier for other reasons. Incrementing the values stored for an existing key does not update its expiration time [1].

Data may be evicted if the Memcache service is restarted for planned or unplanned maintenance [2]

These reasons have been mentioned here:

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 data center maintenance events may also flush some or all of the cache [2]

While memcache is resilient to server failures, memcache values are not saved to disk, so a service failure can cause values to become unavailable. In general, an application should not expect a cached value to always be available.

Can you please confirm whether you set any expiration value for the data stored in Dedicated Memcache. The expiration time being set to the same timestamp for all of your keys could potentially explain this behavior. You can get an idea how the expiration values (in seconds) are set for memcache in the following link [3].

If the above mentioned reason is not the cause why Dedicated Memcache is flushing out data at a particular time of the day, please provide the “Project Id” by going to the following link which will be reported as a “Private Issue” (not visible to the public) to the Google Cloud Support team to look further into the matter.

https://issuetracker.google.com/issues/new?component=187164&template=803901 

[1] https://cloud.google.com/appengine/articles/best-practices-for-app-engine-memcache

[2] https://cloud.google.com/appengine/docs/standard/python/memcache/

[3] https://cloud.google.com/appengine/docs/standard/python/memcache/using

On Wednesday, October 17, 2018 at 4:12:16 AM UTC-4, Shashikanth Reddy wrote:

This is happening even when there is nothing going on and even when the memcache is less.
What may be the reason for this?