Trivial If case of DebugLevel=3 each process writes something like this to the log:
2671:20141014:142720.613 [Z3005] query failed: [2006] MySQL server has gone away [select h.hostid,h.host,h.name,t.httptestid,t.name,t.variables,t.headers,t.agent,t.authentication,t.http_user,t.http_password,t.http_proxy,t.retries,t.ssl_cert_file,t.ssl_key_file,t.ssl_key_password,t.verify_peer,t.verify_host from httptest t,hosts h where t.hostid=h.hostid and t.nextcheck<=1413286040 and mod(t.httptestid,1)=0 and t.status=0 and h.proxy_hostid is null and h.status=0 and (h.maintenance_status=0 or h.maintenance_type=0)] 2671:20141014:142720.613 [Z3001] connection to database 'zabbix' failed: [2002] Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2) 2671:20141014:142720.614 database is down: reconnecting in 10 seconds ... 2671:20141014:142730.614 database connection re-established
So we see when it failed and when it recovered.
In case of DebugLevel=2 the outpus it the following:
3426:20141014:152450.077 [Z3005] query failed: [2006] MySQL server has gone away [select hostid,key_,state,evaltype,formula,error,lifetime from items where itemid=24900] 3426:20141014:152450.077 [Z3001] connection to database 'zabbix' failed: [2002] Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)
and there is no messages that would inform about sucessfull reconnection.