Re: Shell startup, aliases vs. functions vs. autoloadable functions, and zcompile benefits

[Zach Riggle <zachriggle@gmail.com>]

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Good points all around!  I did play around with hyperfine compiling all zsh
scripts in ~/.zprezto and didn't see a tangible difference.

The benchmark I used

$ hyperfine 'zsh -i -l "exit 0"'


Obviously this is not the BEST benchmark, but it is useful for checking
shell startup time -- I might give zsh-bench a look.  I did spend a lot of
time with zprof to benchmark my init scripts, but the most time-consuming
is simply the "source" statement loading other things, but there's no
context as to WHICH files being sourced take the most time.

> you might end up with a mismatched zwc with greater mtime.

This is something I expected to cause hard-to-diagnose problems.  Luckily,
the most common way I'd change files inadvertently (git checkout
branchname) does not use the time from the commit.

I would expect that the md5sum of a file is reasonably fast, and could be
stored in the .zwc for sanity checking, instead of just the "newer than"
check.

> Again you're unlikely to notice unless your $fpath entries are numerous
and deep

> The tradeoff is that the third one occupies less memory than either of
the other two (though about the same as the alias) which is significant if
there are a lot of seldom-used functions.

I expect that I have more $fpath entries than usual, but the total number
of autoloadable functions is much more.

$ echo $#fpath
22

$ for d in $fpath; do n=$(ls $d/* | wc -l); echo "$n $d"; done | sort -nr |
head -3
    1162 /usr/share/zsh/5.8/functions
     559 /usr/share/zsh/site-functions
     141 /Users/zachriggle/.zprezto/modules/completion/external/src


*Zach Riggle*


On Sat, Nov 27, 2021 at 2:22 PM Bart Schaefer <schaefer@brasslantern.com>
wrote:

> On Sat, Nov 27, 2021 at 12:33 AM Roman Perepelitsa
> <roman.perepelitsa@gmail.com> wrote:
> >
> > On Sat, Nov 27, 2021 at 9:11 AM Zach Riggle <zachriggle@gmail.com>
> wrote:
> > >
> > > alias foo='foo --flag1 --flag2'
> > > foo() { command foo --flag1 --flag2 "$@" }
> > > autoloadable module containing (2)
> >
> > In theory the first and the last should have the same performance and
> > the middle should be slower because it has to parse the body. In
> > practice you won't find any difference: zsh parser is very fast.
>
> This is true for shell startup time; at runtime there's a small
> penalty for the middle one (allocating the function context) and on
> the very first execution there's an additional load-time cost for the
> third one.  Again you're unlikely to notice unless your $fpath entries
> are numerous and deep.
>
> The tradeoff is that the third one occupies less memory than either of
> the other two (though about the same as the alias) which is
> significant if there are a lot of seldom-used functions.
>
> Otherwise, everything Roman said.
>

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