PWL NY: Simple Testing Can Prevent Most Critical Failures

Transcript

1. Simple Testing Can Prevent Most Critical Failures: An Analysis of Production Failures in Distributed Data-Intensive Systems Papers We Love New York - June 2016
2. Caitie McCaffrey @caitie Distributed Systems Engineer CaitieM.com
5. Analyzed Failures in Real World Systems
6. “A majority (77%) of failures require more than one input event to manifest, but most of the failures (90%) require no more than 3” Complexity of Failures
7. “The specific order of events is important in 88% of the failures that require multiple events Complexity of Failures
8. “3 Nodes or less can reproduce 98% of Failures” Complexity of Failures
9. Unit Tests “A majority of production failures (77%) can be reproduced by a unit test”
10. Top Down Fault Injection & State Space Exploration is Expensive
11. Logging • 76% of the failures print explicit failure- related error messages • For 84% of the failures, all of the triggering events are logged • Logs are noisy: each failure prints 824 log messages (median)
12. Catastrophic Failures
13. Error Handling • 92% of failures were the result of incorrect handling of non-fatal errors • 58% of faults could have been detected via simple testing • 35% of failures caused by bad practices in error handling code
14. • Error Handling Code is simply empty or only contains a Log statement • Error Handler aborts cluster on an overly general exception • Error Handler contains comments like FIXME or TODO Bad Practices
15. Aspirator Performs static analysis of Java bytecode to detect: • error handler is empty • error handler over-catches exceptions and aborts • error handler contains phrases like “TODO” or “FIXME”
16. • 500 New Bugs & Bad Practices • 115 Fasle Positives • 171 bugs reported • 143 bugs confirmed or fixed Aspirator Results
17. -developer “I fail to see the reason to handle every exception” Developer Reactions
18. “It is often much harder to reason about the correctness of a system’s abnormal path than its normal execution path ”
19. Moving Forward • Use a tool like Aspirator that is capable of identifying trivial bugs • Enforce code reviews of error handling code • High code coverage on error handling code
20. Questions @caitie