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analyses: add README.md 

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>
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Valentin Rothberg 2019-07-08 14:04:32 +02:00
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# A set of scripts and instructions that help to analyze and debloat go-lang dependencies.
## Size of packages
To analyze the size of all go packages used during the build process, pass the `-work -a` build flags to `go build`.
The `-a` flag forces go to rebuild all packages even if they are already up-to-date (e.g., in the build cache), while the `-work` flag instructs go to print path of the temporary work directory used for compiling the packages.
The path to the temporary work directory of `go-build` must be passed to `go-archive-analysis.sh` by setting it as an environment variable.
The analysis script will then read and parse the build data and print a sorted table of the package size in bytes followed by the package name.
Running such an analysis on libpod may look as follows:
```
# 1) Build the podman binary with `-work -a`.
[libpod]$ BUILDFLAGS="-work -a" make podman
[...]
WORK=/tmp/go-build794287815
# 2) Set the work directory as an environment variable and call the analysis script
[libpod]$ WORK=/tmp/go-build794287815 ./dependencies/analyses/go-archive-analysis.sh | head -n10
17M github.com/containers/libpod/cmd/podman/cliconfig
13M github.com/containers/libpod/vendor/github.com/DataDog/zstd
10M github.com/containers/libpod/vendor/k8s.io/api/core/v1
3.7M net/http
3.7M github.com/containers/libpod/libpod
3.2M runtime
2.7M github.com/containers/libpod/vendor/github.com/gogo/protobuf/proto
2.5M github.com/containers/libpod/vendor/k8s.io/apimachinery/pkg/apis/meta/v1
2.3M github.com/containers/libpod/vendor/github.com/vishvananda/netlink
2.1M github.com/containers/libpod/cmd/podman/varlink
```
The output of the `go-archive-analysis.sh` script is a sorted table with the size in bytes followed by the package.
The size denotes the size of the compiled package (i.e., the `.a` file).
## Size of symbols in binary
Once the binary is compiled, we can run another set of analyses on it.
The `nm-symbols-analysis.sh` is a wrapper around `go tool nm` and prints a table with size in bytes followed by the symbols name.
To avoid information overload, the scripts prints only symbols from the text/code segment.
Running such an analysis on libpod may look as follows:
```
# 1) Compile the binary
[libpod]$ make podman
[...]
# 2) Run the script with the binary as an argument
[libpod]$ ./dependencies/nm-symbols-analysis.sh ./bin/podman | grep "containers/libpod/libpod" | head -n10
299 github.com/containers/libpod/libpod.(*BoltState).AddContainer
658 github.com/containers/libpod/libpod.(*BoltState).AddContainerToPod
2120 github.com/containers/libpod/libpod.(*BoltState).AddPod
3773 github.com/containers/libpod/libpod.(*BoltState).AddPod.func1
965 github.com/containers/libpod/libpod.(*BoltState).AddVolume
1651 github.com/containers/libpod/libpod.(*BoltState).AddVolume.func1
558 github.com/containers/libpod/libpod.(*BoltState).AllContainers
282 github.com/containers/libpod/libpod.(*BoltState).AllContainers.func1
1121 github.com/containers/libpod/libpod.(*BoltState).AllContainers.func1.1
558 github.com/containers/libpod/libpod.(*BoltState).AllPods
```
Running the script can help identify sources of bloat and reveal potential candidates (e.g., entire packages, types, or function) for refactoring.