gctrace

README

Memory Tracing

There is no way to identify specifically in the code where a leak is occuring. We can validate if a memory leak is present and which functions or methods are producing the most allocations.

GODEBUG

To validate any sort of potential memory problems, including memory leaks, use the GODEBUG environmental variable.

Setting gctrace=1 causes the garbage collector to emit a single line to standard error at each collection, summarizing the amount of memory collected and the length of the pause. Setting gctrace=2 emits the same summary but also repeats each collection. The format of this line is subject to change:

export GODEBUG=gctrace=1

gc # @#s #%: #+...+# ms clock, #+...+# ms cpu, #->#-># MB, # MB goal, # P

Where the fields are as follows:

gc #        the GC number, incremented at each GC
@#s         time in seconds since program start
#%          percentage of time spent in GC since program start
#+...+#     wall-clock/CPU times for the phases of the GC
#->#-># MB  heap size at GC start, at GC end, and live heap
# MB goal   goal heap size
# P         number of processors used

In C++, a memory leak is memory you have lost a reference to. In Go, a memory leak is memory you retain a reference to.

Running a GODEBUG GC Trace

go build
GODEBUG=gctrace=1 ./gctrace

gc 1 @0.009s 1%: 0.059+0.17+0.005+0.24+0.12 ms clock, 0.17+0.17+0+0/0.36/0.067+0.38 ms cpu, 5->5->3 MB, 4 MB goal, 8 P
gc 2 @0.017s 1%: 0.037+0.096+0.098+0.21+0.086 ms clock, 0.22+0.096+0+0.10/0.31/0.091+0.51 ms cpu, 8->8->7 MB, 7 MB goal, 8 P
gc 3 @0.032s 1%: 0.020+0.16+0.007+0.25+0.090 ms clock, 0.14+0.16+0+0/0.20/0.27+0.63 ms cpu, 17->17->14 MB, 14 MB goal, 8 P
gc 4 @0.066s 0%: 0.029+0.17+0.074+0.48+0.10 ms clock, 0.20+0.17+0+0/0.42/0.26+0.76 ms cpu, 35->35->29 MB, 29 MB goal, 8 P

Links

https://golang.org/pkg/runtime
https://www.hakkalabs.co/articles/finding-memory-leaks-go-programs
http://golang.org/pkg/runtime/
[http://dave.cheney.net/2014/07/11/visualising-the-go-garbage-collector](Visualising the Go garbage collector)
[http://dave.cheney.net/2015/11/29/a-whirlwind-tour-of-gos-runtime-environment-variables](Tour of Go's env variables)
[https://deferpanic.com/blog/understanding-golang-memory-usage](Understanding Go memory usage)

Code Review

Memory Trace (Go Playground)

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All material is licensed under the Apache License Version 2.0, January 2004.

Documentation

Overview

Sample program to see what a memory leak looks like.