Shell startup overhead looks a bit high with mise (up to ~80 ms)

[azhuchkov]

I ran some performance validation using zsh-bench, and it seems that mise adds up to ~80 ms to shell startup on my machine, which feels a bit high compared to the numbers stated in the docs.

Here are the results (zsh 5.8, clean mise install without toolsets, the only init code: eval "$($HOME/.local/bin/mise activate zsh)"):

creates_tty=0
has_compsys=0
has_syntax_highlighting=0
has_autosuggestions=0
has_git_prompt=0
first_prompt_lag_ms=97.518
first_command_lag_ms=97.749
command_lag_ms=25.123
input_lag_ms=0.337
exit_time_ms=70.857

And the same with the --shims option:

creates_tty=0
has_compsys=0
has_syntax_highlighting=0
has_autosuggestions=0
has_git_prompt=0
first_prompt_lag_ms=47.065
first_command_lag_ms=47.283
command_lag_ms=0.116
input_lag_ms=0.338
exit_time_ms=46.642

For comparison, the no-rcs profile from zsh-bench:

creates_tty=0
has_compsys=0
has_syntax_highlighting=0
has_autosuggestions=0
has_git_prompt=0
first_prompt_lag_ms=15.874
first_command_lag_ms=16.104
command_lag_ms=0.113
input_lag_ms=0.324
exit_time_ms=8.174

Of course, these values aren’t huge on their own, but the problem is that they tend to accumulate across different tools, making shell initialization noticeably slower.

[jdx]

I think you can set MISE_TIMINGS=1 to see what it’s doing

[azhuchkov]

@jdx thanks for pointing this out.

Here is a trace of standard activation:

$ zsh -f
host% export MISE_TIMINGS=1
host% eval "$($HOME/.local/bin/mise activate zsh)"
[TIME] 1 mise::cli::logger 25.6ms
[TIME] 1 mise::cli::handle_shim 734µs
[TIME] 5 mise::toolset::install_state::init_plugins 744µs
[TIME] 3 mise::toolset::install_state::init_tools 3.6ms
[TIME] 1 mise::cli::backend::load_tools 21.2ms
[TIME] 1 mise::cli::get_matches_from 19.7ms
[TIME] 1 mise::cli::add_cli_matches 304µs
[TIME] 1 mise::cli::settings 247µs
[TIME] 1 mise::cli::logger 1µs
[TIME] 1 mise::cli::migrate 161µs
[TIME] 1 mise::cli::run activate 4.3ms
[TIME] 1 mise::main 77.8ms
[TIME] 1 mise::cli::logger 2.5ms
[TIME] 1 mise::cli::handle_shim 13µs
[TIME] 7 mise::toolset::install_state::init_plugins 63µs
[TIME] 9 mise::toolset::install_state::init_tools 701µs
[TIME] 1 mise::cli::backend::load_tools 3.0ms
[TIME] 1 mise::cli::get_matches_from 4.8ms
[TIME] 1 mise::cli::add_cli_matches 16µs
[TIME] 1 mise::cli::settings 371µs
[TIME] 1 mise::cli::logger 2µs
[TIME] 1 mise::cli::migrate 76µs
[TIME] 1 mise::config::config::load idiomatic_files 1.1ms
[TIME] 1 mise::config::config::load config_paths 1.2ms
[TIME] 1 mise::config::config::load config_files 3.3ms
[TIME] 1 mise::config::config::load warn_about_idiomatic_version_files 66µs
[TIME] 1 mise::config::config::load vars_results 1.5ms
[TIME] 1 mise::config::config::load validate 17µs
[TIME] 1 mise::config::config::load all_aliases 691µs
[TIME] 1 mise::config::config::load redactions 709µs
[TIME] 1 mise::config::config::load install_state 27µs
[TIME] 1 mise::config::config::load remove_aliased_tools 488ns
[TIME] 1 mise::config::load config 13.9ms
[TIME] 1 mise::toolset::toolset::list_missing_versions 105µs
[TIME] 1 mise::cli::run hook-env 35.5ms
[TIME] 1 mise::main 46.7ms
[TIME] 1 mise::cli::logger 2.5ms
[TIME] 1 mise::cli::handle_shim 10µs
[TIME] 8 mise::toolset::install_state::init_plugins 38µs
[TIME] 7 mise::toolset::install_state::init_tools 787µs
[TIME] 1 mise::cli::backend::load_tools 3.0ms
[TIME] 1 mise::cli::get_matches_from 2.7ms
[TIME] 1 mise::cli::add_cli_matches 16µs
[TIME] 1 mise::cli::settings 362µs
[TIME] 1 mise::cli::logger 2µs
[TIME] 1 mise::cli::migrate 98µs
[TIME] 1 mise::config::config::load idiomatic_files 162µs
[TIME] 1 mise::config::config::load config_paths 1.3ms
[TIME] 1 mise::config::config::load config_files 1.2ms
[TIME] 1 mise::config::config::load warn_about_idiomatic_version_files 7µs
[TIME] 1 mise::config::config::load vars_results 252µs
[TIME] 1 mise::config::config::load validate 4µs
[TIME] 1 mise::config::config::load all_aliases 95µs
[TIME] 1 mise::config::config::load redactions 22µs
[TIME] 1 mise::config::config::load install_state 4µs
[TIME] 1 mise::config::config::load remove_aliased_tools 259ns
[TIME] 1 mise::config::load config 5.5ms
[TIME] 1 mise::cli::run hook-env 7.0ms
[TIME] 1 mise::main 16.1ms

Then after hitting the enter key:

host%
[TIME] 1 mise::cli::logger 26.7ms
[TIME] 1 mise::cli::handle_shim 609µs
[TIME] 5 mise::toolset::install_state::init_plugins 845µs
[TIME] 5 mise::toolset::install_state::init_tools 4.3ms
[TIME] 1 mise::cli::backend::load_tools 23.2ms
[TIME] 1 mise::cli::get_matches_from 25.5ms
[TIME] 1 mise::cli::add_cli_matches 458µs
[TIME] 1 mise::cli::settings 371µs
[TIME] 1 mise::cli::logger 2µs
[TIME] 1 mise::cli::migrate 218µs
[TIME] 1 mise::config::config::load idiomatic_files 1.3ms
[TIME] 1 mise::config::config::load config_paths 1.1ms
[TIME] 1 mise::config::config::load config_files 7.2ms
[TIME] 1 mise::config::config::load warn_about_idiomatic_version_files 34µs
[TIME] 1 mise::config::config::load vars_results 2.5ms
[TIME] 1 mise::config::config::load validate 68µs
[TIME] 1 mise::config::config::load all_aliases 561µs
[TIME] 1 mise::config::config::load redactions 440µs
[TIME] 1 mise::config::config::load install_state 18µs
[TIME] 1 mise::config::config::load remove_aliased_tools 440ns
[TIME] 1 mise::config::load config 18.8ms
[TIME] 1 mise::cli::run hook-env 24.6ms
[TIME] 1 mise::main 108.7ms

Well, another attempt gave different result:

zsh -f
host% export MISE_TIMINGS=1
host% eval "$($HOME/.local/bin/mise activate zsh)"
[TIME] 1 mise::cli::logger 2.3ms
[TIME] 1 mise::cli::handle_shim 9µs
[TIME] 6 mise::toolset::install_state::init_plugins 82µs
[TIME] 9 mise::toolset::install_state::init_tools 959µs
[TIME] 1 mise::cli::backend::load_tools 3.4ms
[TIME] 1 mise::cli::get_matches_from 2.5ms
[TIME] 1 mise::cli::add_cli_matches 10µs
[TIME] 1 mise::cli::settings 196µs
[TIME] 1 mise::cli::logger 1µs
[TIME] 1 mise::cli::migrate 119µs
[TIME] 1 mise::cli::run activate 945µs
[TIME] 1 mise::main 9.8ms
[TIME] 1 mise::cli::logger 1.4ms
[TIME] 1 mise::cli::handle_shim 16µs
[TIME] 2 mise::toolset::install_state::init_plugins 28µs
[TIME] 6 mise::toolset::install_state::init_tools 424µs
[TIME] 1 mise::cli::backend::load_tools 1.8ms
[TIME] 1 mise::cli::get_matches_from 2.1ms
[TIME] 1 mise::cli::add_cli_matches 12µs
[TIME] 1 mise::cli::settings 190µs
[TIME] 1 mise::cli::logger 1µs
[TIME] 1 mise::cli::migrate 45µs
[TIME] 1 mise::config::config::load idiomatic_files 124µs
[TIME] 1 mise::config::config::load config_paths 1.1ms
[TIME] 1 mise::config::config::load config_files 418µs
[TIME] 1 mise::config::config::load warn_about_idiomatic_version_files 14µs
[TIME] 1 mise::config::config::load vars_results 94µs
[TIME] 1 mise::config::config::load validate 2µs
[TIME] 1 mise::config::config::load all_aliases 42µs
[TIME] 1 mise::config::config::load redactions 11µs
[TIME] 1 mise::config::config::load install_state 2µs
[TIME] 1 mise::config::config::load remove_aliased_tools 218ns
[TIME] 1 mise::config::load config 3.2ms
[TIME] 1 mise::toolset::toolset::list_missing_versions 67µs
[TIME] 1 mise::cli::run hook-env 6.2ms
[TIME] 1 mise::main 12.1ms
[TIME] 1 mise::cli::logger 2.1ms
[TIME] 1 mise::cli::handle_shim 9µs
[TIME] 6 mise::toolset::install_state::init_plugins 58µs
[TIME] 9 mise::toolset::install_state::init_tools 834µs
[TIME] 1 mise::cli::backend::load_tools 3.4ms
[TIME] 1 mise::cli::get_matches_from 2.9ms
[TIME] 1 mise::cli::add_cli_matches 14µs
[TIME] 1 mise::cli::settings 265µs
[TIME] 1 mise::cli::logger 1µs
[TIME] 1 mise::cli::migrate 75µs
[TIME] 1 mise::config::config::load idiomatic_files 138µs
[TIME] 1 mise::config::config::load config_paths 1.1ms
[TIME] 1 mise::config::config::load config_files 705µs
[TIME] 1 mise::config::config::load warn_about_idiomatic_version_files 5µs
[TIME] 1 mise::config::config::load vars_results 189µs
[TIME] 1 mise::config::config::load validate 3µs
[TIME] 1 mise::config::config::load all_aliases 69µs
[TIME] 1 mise::config::config::load redactions 16µs
[TIME] 1 mise::config::config::load install_state 3µs
[TIME] 1 mise::config::config::load remove_aliased_tools 480ns
[TIME] 1 mise::config::load config 4.6ms
[TIME] 1 mise::cli::run hook-env 5.2ms
[TIME] 1 mise::main 14.2ms
host%
[TIME] 1 mise::cli::logger 1.6ms
[TIME] 1 mise::cli::handle_shim 7µs
[TIME] 8 mise::toolset::install_state::init_plugins 22µs
[TIME] 5 mise::toolset::install_state::init_tools 363µs
[TIME] 1 mise::cli::backend::load_tools 1.9ms
[TIME] 1 mise::cli::get_matches_from 2.3ms
[TIME] 1 mise::cli::add_cli_matches 12µs
[TIME] 1 mise::cli::settings 244µs
[TIME] 1 mise::cli::logger 1µs
[TIME] 1 mise::cli::migrate 81µs
[TIME] 1 mise::config::config::load idiomatic_files 128µs
[TIME] 1 mise::config::config::load config_paths 1.0ms
[TIME] 1 mise::config::config::load config_files 566µs
[TIME] 1 mise::config::config::load warn_about_idiomatic_version_files 5µs
[TIME] 1 mise::config::config::load vars_results 100µs
[TIME] 1 mise::config::config::load validate 2µs
[TIME] 1 mise::config::config::load all_aliases 42µs
[TIME] 1 mise::config::config::load redactions 12µs
[TIME] 1 mise::config::config::load install_state 2µs
[TIME] 1 mise::config::config::load remove_aliased_tools 131ns
[TIME] 1 mise::config::load config 3.5ms
[TIME] 1 mise::cli::run hook-env 3.9ms
[TIME] 1 mise::main 10.3ms

So, the result is varying for some reason (nothing has changed between runs, 2 tools installed). But zsh-bench which runs 16 iterations by default clearly shows noticable increase in timings: +100ms on first prompt (and command) lag, +30ms on command lag and +60ms on exit time lag.

[Konfekt]

Hello, it's around 300ms on my machine, and I wonder how to reduce it. This issue seems rather to document then discuss or solve it

[Konfekt]

For example, could mise::cli::run hook-env be delayed ?

[iambadwithname]

I use fish and it took ~25ms to activate.
Time (μs) Sum (μs) Command
249 25053 -> source $file
12 24583 --> __mise_env_eval
I notice that "mise activate fish" is calling __mise_env_eval
and __mise_env_eval is also call again at (the start + every cd(change dir))
so I think calling __mise_env_eval in the activate script is unnecessary

[jdx]

@iambadwithname Good catch. I reran this with actual Fish 4.8.1. The early-exit path means the second call is not another full hook-env, but it is not free either.

Using the current checkout with an isolated empty configuration (2026.7.10-DEBUG):

• unchanged-session early exit through Fish: 6.93 ms mean (100 runs)
• forced full hook-env through Fish: 14.51 ms mean (30 runs)
• complete Fish activation with hook: 29.50 ms mean (30 runs)
• complete Fish activation with --no-hook-env: 14.52 ms mean (100 runs)

The explicit __mise_env_eval during activation has no previous __MISE_SESSION, so it must perform the full refresh and establish the environment/session snapshot. When the first fish_prompt event invokes it again, the unchanged-session fast path exits before backend and config loading, but still pays process/runtime startup and change-checking costs—about 7 ms here.

I implemented a one-shot prompt skip in PR #11130. It preserves the immediate refresh and direct __mise_env_eval calls, but skips the first event-driven prompt dispatch after activation. A paired Fish benchmark through the first prompt improved from 36.83 ms to 29.88 ms on average across 30 runs, saving 6.95 ms in this debug-build setup.

Removing the immediate call entirely would mostly move the roughly 15 ms full refresh to the first prompt, and could break later config.fish lines that expect mise-provided tools or environment variables to be available immediately.

These are debug-build timings, so the relative comparison is more meaningful than the absolute numbers.

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