Error grouping is the process an error monitoring tool uses to collapse many individual error events into a single item that represents one underlying bug. Without it, a fault on a hot code path produces one alert per request, and a single null check failure can generate tens of thousands of notifications in an hour.
Grouping quality decides whether your error feed is readable. Group too aggressively and two unrelated bugs land in the same item. Group too loosely and one bug splits into hundreds.
Example
TypeError: Cannot read properties of undefined (reading 'email')
at renderProfile (/app/src/Profile.js:42:19)
at renderWithHooks (/app/node_modules/react-dom/cjs/react-dom.development.js:14985:18)
at mountIndeterminateComponent (/app/node_modules/react-dom/cjs/react-dom.development.js:17811:13)
Ten thousand page loads hit that line. Error grouping turns 10,000 occurrences into one item with a count of 10,000.
What Rollbar does about error grouping
Rollbar groups occurrences into items by computing an identity hash for each occurrence and matching it against hashes already seen in the same project and environment. Rollbar first drops stack frames it already knows are noise, such as direct recursive calls. Rollbar’s basic fingerprinting algorithm then combines the filename, the method name, and the code context (the source line) of each remaining frame, appends the exception class name, and takes the SHA1 hash of the result.
Rollbar excludes line numbers from that fingerprint, so adding a line at the top of a file does not split one bug into two items. Editing the source line inside a frame does change the fingerprint, and can split what was one item into two.
Rollbar also recognizes frequently occurring error types using patterns identified by machine learning rather than hard-coded rules, and lets you override the default with custom fingerprinting rules when it splits or merges something wrongly.
Related terms
Rollbar’s free plan includes 5,000 occurrences a month. Create an account or read the error monitoring overview.
Sources
- Rollbar Docs, Default Grouping Algorithm: https://docs.rollbar.com/docs/grouping-algorithm
- Rollbar Docs, Rollbar Terminology: https://docs.rollbar.com/docs/rollbar-terminology
