godoc memory leak

[christop...@wework.com]

Hi all,

I've been playing around with an internal godoc server and noticed that over long periods of time the memory growth is unbounded. The command I use to invoke godoc is godoc -index=true -index_interval=15m -index_throttle=.30 -maxresults=0. The following images below track the memory usage and change in memory usage over a 24 hour period on a 8 GiB machine. I've also attached a pdf with the data points I gathered during the experiment. Notice how the godoc process consumes 76% of memory by the end of the experiment. Is this indicative of a memory leak in the godoc source code or is this expected behavior?

[Agniva De Sarker]

Couple of questions:

1. What version of godoc and Go are you using ? What is your go env ?

2. You are using -index but not passing an index file. Any reason for that ? godoc will load faster if you write an index beforehand and pass that.

3. I am guessing since you have set index_interval, you expect files to be added in your GOPATH. How many new files are getting added while godoc is running ?

4. Please show us the output by adding -v flag.

[Christopher Dang]

Hello Agniva,

Here is the information you've asked for:

go version: 1.12.0

godoc version: latest

I don't read from an index file because I need live updating from godoc and boot time isn't a high priority. This is because the service I'm creating can expect many files to be added, removed, or updated while godoc is running. While it would be convenient to restart godoc between file system changes my superiors would prefer I not use this option.

I've attached a log dump from godoc -v below. 

I'm running the godoc process from within a docker so I use three methods to measure the memory usage:

1.) I docker exec into the container and run top. The VSZ% is the stat I use to measure memory from inside the docker.

2.) I run docker stats on the container from my host process

3.) since I run godoc with the verbose flag I get logs that tell me how many bytes are consumed by godoc. Example:

2019/06/17 23:28:26 index updated (88.264700559s, 211342912 bytes of source, 17421 files, 6533095 lines, 173980 unique words, 8997500 spots)
2019/06/17 23:28:26 before GC: bytes = 2385978984 footprint = 6429047608
2019/06/17 23:28:26 after  GC: bytes = 614368968 footprint = 6429047608

The charts and excel sheet above get their data points from godoc's footprint logs. I double check every now and then that footprint's output is accurate by comparing it against top and docker stats. 

The docker image is golang:1.12.0-alpine3.9

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[Agniva De Sarker]

I can see that files are getting added. Which means index size is expected to increase. But it seems sometimes it is increasing even when there is no change.

Could you please file an issue so that folks can investigate this ? Thanks.

[Christopher Dang]

Thanks for the feedback. For anyone experiencing this issue you can follow it here: https://github.com/golang/go/issues/32692

[Tom Mitchell]

On Mon, Jun 17, 2019 at 9:40 PM Agniva De Sarker <agniva.qu...@gmail.com> wrote:

Couple of questions:

1. What version of godoc and Go are you using ? What is your go env ?

One other question ...
If the OS supports limits does godoc fail nicely with smaller limits.
I am reminded of student code that would malloc(to-infinity-and-beyond) because
student accounts had user limits and often began with a malloc() loop to get 
the largest amount possible to ease programming and speed things up.

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   T o m    M i t c h e l l

[Christopher Dang]

When I ran the godoc service in a docker image with less memory (6 GiB) the behavior was the same. For both a 8 GiB and 6 GiB machine, the godoc process continue to consume memory until it surpasses the memory on the machine and crashes. After the crash, the other processes on my machine continue to work and the memory is freed back entirely to the machine. 

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[Tom Mitchell]

Thanks! 

[e...@coip.me]

wrt tracing out leaks, pprof is insanely powerful and relatively easy to add in.