Bash completion slows down bash login sessions

[hoxu]

• I have tried with the latest version of Docker Desktop
• I have tried disabling enabled experimental features
• I have uploaded Diagnostics
• Diagnostics ID:

Expected behavior

bash_completion.d/docker should be fast to execute. It probably should not make any docker calls until actually needed.

Actual behavior

Executing the bash completion script causes a noticeable pause when opening new bash sessions.

The slowest part is a call to docker:

+++ [[ -r /usr/local/etc/bash_completion.d/docker ]]
+++ . /usr/local/etc/bash_completion.d/docker
+++++ shopt -p extglob
++++ __docker_previous_extglob_setting='shopt -s extglob'
++++ shopt -s extglob
+++++ docker info --format '{{range .ClientInfo.Plugins}}{{if eq .Name "compose"}}{{.Path}}{{end}}{{end}}'

This seems to be:

COMPOSE_PLUGIN_PATH=$(docker info --format '{{range .ClientInfo.Plugins}}{{if eq .Name "compose"}}{{.Path}}{{end}}{{end}}')

$ time docker info --format '{{range .ClientInfo.Plugins}}{{if eq .Name "compose"}}{{.Path}}{{end}}{{end}}'
/usr/local/lib/docker/cli-plugins/docker-compose

real    0m2.538s
user    0m0.142s
sys     0m0.085s

Information

• macOS Version:
• Intel chip or Apple chip:
• Docker Desktop Version: 4.14.1 (91661)

Output of /Applications/Docker.app/Contents/MacOS/com.docker.diagnose check

N/A

Steps to reproduce the behavior

Open a new bash login session.

To visually see what is taking up time:

bash -lx

[thaJeztah]

Thanks for reporting; this looks to be related to changes that were made in the completion script in https://github.com/docker/cli (#3752).

Let me transfer this ticket to the CLI issue tracker (I know some improvements were made after that, but not sure if they can be included in the 20.10 version)

[thaJeztah]

I know some improvements were made after that, but not sure if they can be included in the 20.10 version

Did a quick comparison;

# on docker 20.10;
time $(docker info --format '{{range .ClientInfo.Plugins}}{{if eq .Name "compose"}}{{.Path}}{{end}}{{end}}')
real	0m1.034s
user	0m0.130s
sys	0m0.094s

# on docker 23.0.0-dev
time $(docker info --format '{{range .ClientInfo.Plugins}}{{if eq .Name "compose"}}{{.Path}}{{end}}{{end}}')
real	0m0.196s
user	0m0.136s
sys	0m0.048s

[hoxu]

That's a big improvement, but 0.20 s is still pretty long. If every completion file took that long time, the result would be unbearable.

Could the call to docker be deferred until the information it prints is actually required in the bash session?

[vegerot]

💀

$ docker --version
Docker version 20.10.21, build baeda1f

$ hyperfine --warmup=1 /usr/local/etc/bash_completion.d/docker
Benchmark 1: /usr/local/etc/bash_completion.d/docker
  Time (mean ± σ):     342.8 ms ±  18.5 ms    [User: 161.4 ms, System: 124.2 ms]
  Range (min … max):   308.6 ms … 371.8 ms    10 runs

[vegerot]

☠️

$ docker --version
Docker version 23.0.5, build bc4487a

📁~/
$ hyperfine --warmup=1 /usr/local/etc/bash_completion.d/docker
Benchmark 1: /usr/local/etc/bash_completion.d/docker
  Time (mean ± σ):     223.4 ms ±  13.0 ms    [User: 247.5 ms, System: 200.1 ms]
  Range (min … max):   206.1 ms … 238.9 ms    13 runs

[guss77]

The setting of $DOCKER_PLUGINS_PATH during bash completion initialization looks to be a cache for building the plugin commands during docker command completion.

Why is it done during initialization of every single session instead of only as needed?

If docker info --format '{{range .ClientInfo.Plugins}}{{.Path}}:{{end}}' is that fast that it doesn't slow down bash initialization, then it doesn't need to be cached: it can be run as needed when the user calls for docker command completion; OTOH If it is slow, then it definitely cannot be run during bash completion initialization as that unnecessarily slows down every new session.

Regardless, this should be removed.

[guss77]

I offered a PR #4505 to move that plugins path reading to where it should be.