Question 1

How do I trace a specific function's arguments and return value with Rexbug?

Accepted Answer

Use Rexbug.start with patterns like "Module.function/_ :: return", as shown in the README examples, which traces calls and outputs return values. Add "stack" for stack traces if needed, and specify time or message limits for safety.

Question 2

Is Rexbug safe to use in production environments?

Accepted Answer

Yes, Rexbug includes production-safe limits on time and event counts to prevent system overload, as emphasized in the README. However, always test tracing patterns in development first to avoid accidental performance hits from overly broad traces.

Question 3

Rexbug vs dbg: which is better for Elixir debugging?

Accepted Answer

Rexbug offers Elixir-friendly syntax and integrates :redbug's safety features, while dbg is more battle-tested but may require Erlang familiarity. The README notes Rexbug is less tested than alternatives, so choose based on syntax preference and project maturity.

Question 4

How to debug a remote Elixir node that doesn't have Rexbug installed?

Accepted Answer

Connect from a node with Rexbug loaded, using the target option as demonstrated in the FAQ, where beam files are specified via -pa flags. This allows tracing on remote systems without modifying their dependencies.

Question 5

What performance impact does Rexbug have on a live system?

Accepted Answer

Rexbug adds minimal overhead primarily during trace setup, as syntax translation is a one-time cost. However, tracing itself can affect performance based on volume; use the built-in limits to control this, and opt for file output over console printing in high-load scenarios.

Question 6

Can I use Rexbug to trace messages between processes?

Accepted Answer

Yes, Rexbug supports tracing process messages with options like [:send, :receive] and specifying process IDs, as shown in the message tracing example. This helps investigate inter-process communication in real-time.

Question 7

How do I stop Rexbug tracing once it's started?

Accepted Answer

Call Rexbug.stop() to halt tracing manually, or rely on the timeout or message limits to stop automatically. The README examples show both manual stopping and automatic completion based on configured limits.

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