Friday, August 8, 2014

Email Error Logging Without Breaking The Bank... Literally

Over the years, I've often found that the best way to make enemies with your mail server administrator is to have your system pump a few hundred thousand emails through their server in a short space of time. Never fails...

Sometimes having your system send you it's error logs via mail is the only feasible alternative when you physically can't get to your error logs in a production environment.

Here you are often trying to maintain a balance between sending enough information, as often as possible; and not flooding the mail server when your system decides to have a wobbly.

The solution that I've decided on in the end, should give me the best of both worlds, and has been working very nicely for a few months now.

Simply put, the idea is very simple: Send me everything I need to know, but don't spam me...
My solution was to write a very simple and purpose built "spam filter" within my application.

The basic logic is as follows:

  • Store a key value pair in memory. The key is a hash, and the value is the time in milliseconds 
  • Have a configurable expiry period, whereby you can remove items from the key value pair after a specified time period.
  • Before sending an mail, build a checksum of the mail's body (I use SHA-2 and then store a String Hex representation to save memory).
  • Interrogate your key value pair using the hash that you've just generated
    • If a match is not found, Insert the hash and the current time in milliseconds into the pair and release the mail
    • If a match is found, discard the mail
  • When the configurable expiry time is reached (Current Time in milliseconds - Time in the key value pair), remove the item from the key value pair
In the end it has worked extremely well for me. I don't get mailed about the exact same problem more than once, unless the problem persists past the expiry time.

I hope that this can be of use to you.

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