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debugging-performance-issues.md

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Debugging performance issues

https://jvns.ca/blog/2017/09/24/profiling-go-with-pprof/ https://rakyll.org/custom-profiles/ https://software.intel.com/en-us/blogs/2014/05/10/debugging-performance-issues-in-go-programs

builtin profiles provided by the runtime/pprof

A Profile is a collection of stack traces showing the call sequences that led to instances of a particular event, such as allocation. Packages can create and maintain their own profiles; the most common use is for tracking resources that must be explicitly closed, such as files or network connections.

  • profile: CPU profile determines where a program spends its time while actively consuming CPU cycles.
  • heap: Heap profile reports the currently live allocations; used to monitor current memory usage or check for memory leaks.
  • threadcreate: Thread creation profile reports the sections of the program that lead the creation of new OS threads.
  • goroutine: Goroutine profile report the stack traces of all current goroutines.
  • block: Block profile show where goroutines block waiting on synchronization primitives (including time channels) (disabled by default).
  • mutex: Mutex profile reports the lock contentions. When you think your CPU is not fully utilized due to a mutex contention, use this profile (disabled by default).

pprof basics

  • Setup a webserver for getting Go profiles:

    import _ "net/http/pprof"

  • Go to localhost:$PORT/debug/pprof to get a list of available profiles.

  • Use go tool pprof to analyze profile.

    go tool pprof localhost:$PORT/debug/pprof/$PROFILE_TYPE
# Generate a svg
go tool pprof -svg localhost:$PORT/debug/pprof/$PROFILE_TYPE > $PROFILE_TYPE.svg

NOTE: The trace endpoint (/debug/pprof/trace?seconds=5), unlike all the rest, outputs a file that is not a pprof, it's a trace and you can view it using go tool trace.

heap profile

  • alloc_space vs inuse_space:
-inuse_space      Display in-use memory size
-inuse_objects    Display in-use object counts
-alloc_space      Display allocated memory size
-alloc_objects    Display allocated object counts

// WIP WIP...