zabbix_agent (active) items uses trapper threads right? + trigger question

[SAT QPass]

Observationally, it would seem that when you have an item of the type zabbix_agent (active) it looks to send its data to a trapper thread on the zabbix_server host,right? I just want to make sure I understand and it in turn drives my next question.

As a result, the only way to create an alert on no data received (say the zabbix_agentd on the monitored node dies and stops sending on interval) is to use min/max(time interval) correct (any fucntion that allows for a function of time)? You cannot use the nodata function right? So if you have an item which is fetching a hypothetical integer value of "0" every 60 seconds, what does the expression min(180) return if it has not had any data in the last 3 minutes? 0? Null? The reason I ask is because the obvious trap is that if you are looking for a zero value and min()/max(), etc. return a zero when the evaluating a period with no data, that is BAD. How can you detect a no data event? If it does return zero it should be classified as a bug and instead return null. Could a savy dev type who is familiar with the code comment on this?

If I had one wish it would be that nodata worked for zabbix_agent (active) items in addition to TRAPPER items.

Thanks!

[Alexei]

The function nodata() works for all types of items (active, passive) in ZABBIX 1.1. I amanded ZABBIX Manual, it contained wrong info.

[SAT QPass]

Awesome. That is great news. Thanks for the clarification about nodata.

Also, was my interpretation as two which type of zabbix_server thread a zabbix_agent (active) uses to communicate data?

[Alexei]

Observationally, it would seem that when you have an item of the type zabbix_agent (active) it looks to send its data to a trapper thread on the zabbix_server host,right? I just want to make sure I understand and it in turn drives my next question.

Absolutely right! The agent plays active role in this scenario, it periodically retrieves list of active checks from ZABBIX Server (trapper process) and then sends required information to the server, also to trapper.