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drop init time cost of apd from 0.530ms to 0.002ms #137

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drop init time cost of apd from 0.530ms to 0.002ms #137

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Commits on Aug 20, 2024

  1. delay making global constants via sync.OnceValue 

    As measured by benchinit plus benchstat, this shaves off about 0.46ms
and 1200 allocs from the package's init time, which is fairly noticeable
for any downstream binary's ability to quickly get to its main func.

For example, cuelang.org/go/cmd/cue takes about 4ms to reach main
due to initializing Go packages, so cockroackdb/apd/v3 was to blame
for about 12% of that slowness.

    goos: linux
    goarch: amd64
    cpu: AMD Ryzen 7 PRO 5850U with Radeon Graphics
                              │     old      │                new                 │
                              │    sec/op    │   sec/op     vs base               │
    GithubComCockroachdbApdV3   533.11µ ± 3%   76.33µ ± 3%  -85.68% (p=0.000 n=8)

                              │      old      │                 new                 │
                              │     B/op      │     B/op      vs base               │
    GithubComCockroachdbApdV3   564.05Ki ± 0%   43.91Ki ± 0%  -92.21% (p=0.000 n=8)

                              │     old     │                new                 │
                              │  allocs/op  │  allocs/op   vs base               │
    GithubComCockroachdbApdV3   2.461k ± 0%   1.222k ± 0%  -50.35% (p=0.000 n=8)
    @mvdan
    mvdan committed Aug 20, 2024
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  2. delay making global lookup tables via sync.OnceFunc 

    Thanks to the previous commit delaying the making of global constants,
the tables below are no longer unconditionally needed at init time,
but only as the first API calls come in from user code.

On top of the 0.46ms saving from the previous commit, this change
saves us 0.07ms and over 1100 allocations from init time,
bringing apd/v3's init time cost down to just 0.002ms.

    goos: linux
    goarch: amd64
    cpu: AMD Ryzen 7 PRO 5850U with Radeon Graphics
                              │     mid      │                 new                 │
                              │    sec/op    │    sec/op     vs base               │
    GithubComCockroachdbApdV3   76.325µ ± 3%   2.116µ ± 12%  -97.23% (p=0.000 n=8)

                              │      mid      │                 new                 │
                              │     B/op      │     B/op      vs base               │
    GithubComCockroachdbApdV3   43.914Ki ± 0%   1.539Ki ± 0%  -96.50% (p=0.000 n=8)

                              │     mid      │                new                │
                              │  allocs/op   │ allocs/op   vs base               │
    GithubComCockroachdbApdV3   1222.00 ± 0%   66.00 ± 0%  -94.60% (p=0.000 n=8)
    @mvdan
    mvdan committed Aug 20, 2024
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    fb47fad View commit details
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