Notify upon any serious errors on logs

Sometimes there are severe bugs (new or reintroduced) in productions that go on for days and weeks, and customers do not always notify us. The only tool I have now is grep, awk & perl but I am just being reactive once someone complains.

I want to be proactive and be notified when a certain error has occured for certain number of times in a given time period. But I don't want to be spammed with notifications on every single error.

Are there any lightweight, opensource solutions for a cluster of servers ? Email, SMS or RSS is fine. Also it would be nice to view the reports and trends in a graph too, but not necessary.

Currently I use Apache Log4J, and I know I can send email alerts using it. But as I said, I dont want to be email for every single error开发者_如何学Python. I want to have some intelligence on the system on when it should notify me. And I want that intelligence outside of my application code.

Can you add something that runs once per day that does all the greps you do and either sends or emails you the results? Alternately you can send the results to the customer's admin so they can elevate it to you.