ORA-12154: TNS:could not resolve the connect identifier specified

[mdobrinin]

I am experiencing strange behavior on 2.0.3 server running on VM with Oracle 11g database. The database sits on remote machine. I have everything configured and was polling for data on a host, but would get an error every 10sec or sooner:

ociplogon(): ORA-12516: TNS:listener could not find available handler with matching protocol stack [include/db.inc.php:124]

Zabbix 2.0.3
 
Zabbix is temporarily unavailable!

But it would only be temporary as refreshing the page would take me back to the dashboard or latest data page and I could see values being recorded properly. After restarting the machine, I am no longer able to log in to the front-end because I only see an error screen:

ociplogon(): ORA-12154: TNS:could not resolve the connect identifier specified [include/db.inc.php:124]
Constant ZBX_PAGE_NO_MENU already defined [warning.php:29]
Zabbix 2.0.3
 
Zabbix is temporarily unavailable!

The database is set up correctly, and I can connect to it locally. The tables are set up correctly and there were values being recorded correctly.

The only clues log provided were:

30937:20121101:144118.563 [Z3001] connection to database '//xxx:1521/zabbix' failed: [-1] ORA-12516: TNS:listener could not find available handler with matching protocol stack
30937:20121101:144118.563 Database is down. Reconnecting in 10 seconds.

[mdobrinin]

Looks like the problem is caused by Zabbix front-end creating a lot of sessions, which inevitably reaches Oracle's limit.