Hi,
For some time my company is using zabbix. We have a few hundred servers that we monitor with zabbix with a postgresql database. The database is ~50 GB.
The problem is happening when zabbix server is restarted for some reason and some cache from zabbix have to be flushed to the database. I see active queries in the database similar to this:

update trends set num=60,value_min=100.000000,value_avg=100.000000,value_max=100.000000 where itemid=37068 and clock=1437400800; 
 update trends set num=60,value_min=99.910962,value_avg=99.910995,value_max=99.911000 where itemid=27705 and clock=1437400800;  
update trends set num=60,value_min=0.000000,value_avg=0.000000,value_max=0.000000 where itemid=31660 and clock=1437400800; 
 update trends set num=60,value_min=96.644629,value_avg=96.644700,value_max=96.644709 where itemid=37192 and clock=1437400800; 
... more like this

When this happens, on the postgresql server (which is different server) the full amount of RAM + swap starts to be taken until the whole memory is full and the queries crashes with "out of memory" error.
After a while (~10-20min) all queries like this are over and the server load is back to normal.
The problem is that the updates them-self are not so consuming at all, and I have no idea why it is consuming so much memory. Also in the other time the server is not loaded at all for weeks.
I am attaching my server conf