Recently we migrated our memcached cluster to a new larger one. This needed to be done mostly for reliability and speed, but it’s also nice being able to have access to new stats like ‘reclaimed’ in 1.4.5.
We decided against migrating data from cluster to cluster because there are long-expire keys we no longer care about. Instead, we just ran some scripts to fill the new cluster with new data. After the scripts finished and the new cluster ran in production for a couple days, it only contained ~70% the data the old cluster possessed. We were curious what that old data was, so we decided to dump it and analyze.