Version where reported: 6.0.33

When performing Active Checks, there is a reverse-DNS lookup being made, but there's no indication of that in logs. 

While performance of Zabbix Proxy decreased for unknown reason, it seemed that this query:

select h.hostid,h.status,h.tls_accept,h.tls_issuer,h.tls_subject,h.tls_psk_identity,a.host_metadata,a.listen_ip,a.listen_dns,a.listen_port,a.flags from hosts h left join autoreg_host a on a.proxy_hostid is null and a.host=h.host where h.host='FVXXXXXXXXXX' and h.status in (0,1) and h.flags<>2 and h.proxy_hostid is null] 

is taking very long to execute, but in fact it was very fast (2s), while the whole operation is logged for ~8s in logs.

The reason for it taking so long, was one of the DNS servers was slow.

It has been checked with packet capture that there indeed is a reverse-dns lookup being made, when performing that active check, but it's not being logged.
Therefore problem was not with the proxy/server itself, but rather with DNS server, which took too long to figure out. 

There's a request to include in logs, that the the DNS lookup is being performed.

Steps to reproduce:

1. Have a local DNS resolver
2. Configure active checks to some host
3. Run the packet capture
4. See in packet capture that DNS lookup is being performed at the time of logged Active check in proxy/server

Result:

Expected:
Entries in log, indicating that such operation was performed (DNS lookup), possibly with the time it took.