Debugging high (string) heap usage
I was observing relatively high memory usage in my deno applications (web-applications). I haven't attempted any debugging on my production application, however upon connecting to a debugger locally on my development environment I am seeing high memory size for
(string) and in there it appears a lot of it is coming from std library or other dependency modules. I am attaching the images here for reference, if required I can share the heapsnapshot file through a downloading service since it is around 250MB.
I am trying to understand how or if I can reduce the memory usage of this (string) as majority of the memory usage is happening here.
Any help or reference resource which I can study to debug and solve this issue would be much appreciated, since I am not well-versed with profiling and memory usage I would be happy to learn more if I am missing something here.
3 Replies
Debugging memory usage, especially related to strings, can be a bit complex, but Deno provides tools to help you profile and understand where memory is being used. Here are some steps you can take to debug high string heap usage in your Deno application:
1. Heap Snapshot Analysis: Since you've already taken a heap snapshot, you can analyze it using tools like Chrome DevTools. This will allow you to inspect which strings are taking up space and their retaining paths, which show you why the memory is not being released.
2. Profiling Tools: The documentation mentions tools like
flamegraph-rs and flamescope for visualizing performance profiles. These tools can help you understand the runtime characteristics of your application, including memory usage patterns.
3. V8 Profiling: Deno allows you to use V8's built-in profiling tools. You can run your application with the --prof V8 flag to generate a log file that contains information about function call times and memory usage. This log can be processed with tools like node --prof-process to get a readable format or visualized using the Web UI provided by V8.
4. Deno Flags: There are flags like --trace-asm-time and --use-idle-notification that can help you understand memory usage and potentially reduce the memory footprint. However, these flags are more about tracing and garbage collection hints rather than direct memory usage analysis.
5. Code Review: Review your code and the libraries you are using. Sometimes, high memory usage can be due to holding onto large strings, excessive logging, or not properly releasing resources. Check if there are any patterns or practices in your code or in the libraries that could be optimized.
6. Library Issues: If the memory usage is coming fromthird-party libraries, consider opening an issue in the library's repository. The maintainers might be aware of the issue or have suggestions for reducing memory usage.
7. Update Dependencies: Ensure that you are using the latest versions of Deno and your dependencies, as there may have been memory optimizations in newer releases.
8. Deno Community: Reach out to the Deno community. Other developers might have encountered similar issues and could have insights or solutions.
Remember that some level of string memory usage is normal, especially if your application is string-intensive. However, if you suspect a memory leak or unusually high memory usage, the above steps should help you start investigating the issue.
If you need more specific guidance on using the profiling tools mentioned in the documentation, please let me know, and I can provide further details. 🦕
I tried to update all the dependencies, I am also running deno 1.41.0, I have tried this with deno 1.33.0 as well but there were similar results. After updating the heap usage details are still fairly similar.
