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Understanding Test Results

Test results are stored in store/<test-name>/<timestamp>/. See store/latest for a symlink to the most recently completed test, and store/current for a symlink to the currently executing (or most recently completed) test.

You can view these files at the command line, using a file explorer, or via Maelstrom's built-in web server. Run java -jar maelstrom.jar serve (or lein run serve) to launch the server on port 8080.

Common Files

Each workload generates slightly different files and output, but in every test, you'll find:

  • jepsen.log: The full logs from the test run, as printed to the console.

  • results.edn: The results of the test's checker, including statistics and safety analysis. This structure is also printed at the end of a test.

  • history.edn: The history of all operations performed during the test, including reads, writes, and nemesis operations.

  • history.txt: A condensed, human-readable representation of the history. Columns are process, type, f, value, and error.

  • messages.svg: A spacetime diagram of messages exchanged. Time flows (nonlinearly) from top to bottom, and each node is shown as a vertical bar. Messages are diagonal arrows between nodes, colorized by type. Hovering over a message shows the message itself. Helpful for understanding how your system's messages are flowing between nodes.

  • timeline.html: A diagram where time flows (nonlinearly) down, and each process's operations are arranged in a vertical track. Blue indicates ok operations, orange indicates indefinite (info) operations, and pink indicates failed operations. Helpful in understanding the concurrency structure of the test, as visible to Maelstrom.

  • latency-raw.png: Shows the latency of each Maelstrom operation, plotted over time by the time the request began. Color indicates whether the operation completed with ok, info, or fail. Shape indicates the f function for that operation: e.g. a read, write, cas, etc.

  • latency-quantiles.png: The same latency timeseries, binned by time, intervals and projected to quantiles 0.5, 0.95, 0.99, and 1.

  • rate.png: The overall rate of requests per second, over time, broken down by :f and :type.

  • log/n*.log: The STDERR logs emitted by each node.

  • test.fressian: A machine-readable copy of the entire test, including history and analysis.

Interpreting Results

At the end of each test, Maelstrom analyzes the history of operations using a checker, which produces results. Those results are printed to the console at the end of the test, and also written to results.edn. At a high level, results are a map with a single mandatory keyword, :valid?, which can be one of three values:

  • true: The checker considers this history legal.
  • :unknown: The checker could not determine whether the history was valid. This could happen if, for instance, the history contains no reads.
  • false: The checker identified an error of some kind.

These values determine the colors of test directories in the web interface: blue means :valid? true, orange means :valid? :unknown, and pink means :valid? false. They also determine Jepsen's exit status when running a test: true exits with status 0, 1 indicates a failure, and 2 indicates an :unknown. Other exit statuses indicate internal Jepsen errors, like a crash.

Maelstrom's results are a combination of several different checkers:

  • perf is always valid, and generates performance graphs like latency-raw.png.

  • timeline is always valid, and generates timeline.html

  • exceptions collects unhandled exceptions thrown during the course of a test--for example, if your binary generates malformed RPC responses.

  • stats collects basic statistics: the overall :count of operations, how many were ok, failed, or crashed with info, as well as breakdowns for each function (by-f), so you can see specifically how many reads vs writes failed.

  • net shows network statistics, including the overall number of sent, received, and total unique messages, and breakdowns for traffic between clients and servers vs between servers.

  • workload depends on the checker for that particular workload. See the workload documentation for details.