looks like zabbix server is logging some detailed queries even at loglevel 3 - most likely during the node synchronisation step

for example,

insert into functions (functionid,itemid,triggerid,function,parameter) values (13413400000011301,13413400000017467,13413400000012212,'last','0');

tables that appear in the logfile :

actions
applications
autoreg_host
conditions
config
dchecks
dhosts
drules
dservices
functions
globalmacro
graphs
profiles