An opt-out had to made for the use of DBMainStash for AbuseFilter profiling keys due to the high write rate, which was causing replication lag. Batching the writes (e.g. some kind of mergeMulti will not yelp with mysql).
Perhaps we could either:
a) Stick to a non-replicated redis instance (non-shared between datacenters)
b) Likewise but with mysql
c) Use memcached and broadcast the increment operations, using pipelinine, mcrouter key coalescing (like WANCache), and the latest INCR features in the memcached protocol (will require https://gerrit.wikimedia.org/r/c/mediawiki/core/+/530019 )