LMDB: Environment maxreaders limit reached
Knot 2.2.0 started failing knotc calls accessing the database, e.g. "status", "conf-check" and "zone-status" with the error: "error: failed to open configuration database '/var/lib/knot/confdb' (unknown error -30790)". The error code translates into LMDB's "Environment maxreaders limit reached".
lsof reports 144 open file descriptors for /var/lib/knot/timers/data.mdb and the same for /var/lib/knot/confdb/data.mdb 96 for /var/lib/knot/timers/lock.mdb and the same for /var/lib/knot/confdb/lock.mdb However, killing and starting the daemon temporarily fix the problem, and these numbers will be the same immediately after starting knotd again
(As a side effect, this prevents the daemon from being restarted through the initscript due to "knotc status" failing to run)