Item-too-large for Memcached and Valcache indicate the same thing. The error indicates that a segment was built by Datomic that was too big to store in memcached/valcache. Having these occasionally in your logs is not anything to be concerned about, however, if you create something like a super long string/blob on an attribute you can make a segment that is too large to fit in your cache. I know off the top of my head that the fixed size limit for memcached is 1MB.