We are investigating using Memcached's extstore as a single/non-sharded/non-clustered application cache of data larger than memory. From my reading, it sounds like this is not the typical use case. Due to that, I wanted to see if there were any unintended consequences of our configuration.
Specifically, we are looking to configure extstore with ext_item_age=0. From our initial testing, it looks like this means that this effectively turns Memcached into a mostly disk-based cache of values. In particular, Memcached will attempt to write out pages as soon as they fill to disk. Then, when accessing values, the disk cache -> disk will be used. Is that correct?
We noticed the extstore file grows and the memcache memory stays relatively low. If we wanted to keep more of the recent values in memory, should we just increase the ext_item_age to a couple of hours? Are there unintended consequences of this setup? Any other configuration that we should be looking at?