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Previously in the yr the Undo crew released Live Recorder 5, the hottest version of their “software flight recorder technology” for C/C++, Rust, and Go programs that permits the seize of all nondeterministic info within just an application’s execution for debugging uses. The captured recording allows the recreation of an application’s entire memory and the register state, which supports the replay of execution ways, backwards and forwards, by using the UndoDB debugger. At the current QCon San Francisco convention, InfoQ sat down with Dr Greg Law, co-founder and CTO at Undo, in get to study additional.

As stated on the Undo web page, debugging intermittent software program failures, whether or not in advancement, check, or in output, can be a annoying practical experience for both conclusion people and engineers. Contemporary debuggers for languages like C++ and Go are typically attribute loaded, but they do not seize all related nondeterministic exterior functions that could be expected for the recreation of a bug, and they also only let the debugging of processes executing in a linear vogue.

Mocks and stubs can, of study course, be applied to simulate exterior gatherings and incorporate determinism, and an software can also be executed many occasions during a debugging session. However, these ways include overhead and potential complexity, and are time intensive.

Undo’s Live Recorder captures all nondeterministic data, down to the instruction amount, and this can be applied to recreate an application’s total state. This recording procedure usually benefits in a 2x to 5x slowdown of the focus on software. Live Recorder is only made use of to report unsuccessful processes, and is not meant to be operate constantly like a profiler or other observability tooling.

Information capture is optimized so it can be stored in memory, and the entire program’s memory and register condition can be recreated on demand with minimum overhead. The recorded data can be persisted to a file and shared amongst engineers. Reside Recorder comes with an integrated reversible debugger so the recording can be debugged by replaying it backwards and forwards.

Undo's Live Recorder
Picture taken from Live Recorder Datasheet (PDF)

In discussion with InfoQ, Regulation was distinct to talk that using Stay Recorder really should not be found as an alternate to emitting metrics or logging. Stay Recorder does not intention to notify engineers to the existence of faults or failures in just an application, and this is in its place very best achieved through the use of metric collection and evaluation, exception managing code, and alerting tooling. Logging can also be utilized by engineers to give more context as to what is, or need to be, developing inside of an software at an arbitrary level in execution.


Logging is useful, in that it presents extra context to the organization issue or underlying algorithm. Logging can ‘state what you know’. An exception or stack trace can also give excellent clues as to what is gone incorrect. But generally as an engineer, you only have to have to replay the circumstance that brought about an difficulty, and action-by-move develop a mental model of the situation and the underlying triggers.


Law stated that Live Recorder aims to facilitate the detection and repairing of bugs an engineer has not earlier assumed about, and thus is aiming at aiding the resolution of the “unknown unknowns”. He ongoing by outlining that issue of understanding the causes of a bug can be modelled with a two-dimensional graph, where by the x axis represents how frequently a bug manifests by itself, and the y axis how repeatable the bug is. Live Recorder excels in the bottom correct of this graph, wherever the bug is often remaining viewed, but it can not easily be recurring with common debugging techniques.

As soon as a recording file has been produced that captures a defect, engineers can see the recording to evaluate execution background working with UndoDB, Reside Recorder’s “reversible debugger”. UndoDB is centered on GDB, the GNU Job Debugger, and supports resource-stage debugging for programs penned in any language supported by GDB, which include C/C++, Rust and Ada. UndoDB supports all the anticipated debugging options, with variable and memory inspection, scripting, conditional breakpoints and watchpoints, all in forwards and reverse execution of the application. More characteristics include:

    • Multi-system correlation: reveals the get in which procedures and threads change facts constructions in shared memory.


    • Thread fuzzing: randomizes thread execution to reveal race ailments and other multi-threading flaws.


    • Integration: APIs, CLI, front-close and container system integrations.


    • Compiler- and library-agnostic: Dwell Recorder does not require that application to be recompiled or joined versus certain libraries.


Regulation said that Reside Recorder 5. can also file and replay the execution of unique Kubernetes and Docker containers to assist solve flaws quicker in microservices environments.

Dwell Recorder currently supports C/C++, Go, Rust, Ada purposes on Linux x86 and x86_64, with Java assist coming before long. It is suitable with all mainstream Linux distributions, and no kernel are alterations demanded.

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