Commits on Jul 5, 2024

1. go/mysql: performance optimizations in protocol encoding …

   This employs a couple tricks that combined seemed fruitful:
   
   * Swapping to binary.LittleEndian.Put* on the basic calls gets us a free
     boost while removing code. The main win from this swap is the slice
     boundary check, resulting in a massive boost. I kept it inlined, but
     added my own boundary checking in `writeLenEncInt` since swapping it
     out here resulted in a very minor performance regression from the
     current results. I assume from the extra coersion needed to the uint*
     type, and another reslice.
   * Reslicing the byte slice early so all future operations work on
     0-index rather than pos+ indexing. This seemed to be a pretty sizeable
     win without needing to do more addition on every operation later to
     determine the index, they get swapped out for constants.
   * Read path employs the same early reslicing, but already has explicit
     bounds checks.
   * Rewrite `writeZeroes` to utilize the Go memclr optimization.
   
   ```
   $ benchstat {old,new}.txt
   goos: darwin
   goarch: arm64
   pkg: vitess.io/vitess/go/mysql
                                    │    old.txt     │               new.txt                │
                                    │     sec/op     │    sec/op     vs base                │
   EncWriteInt/16-bit-10               0.4685n ±  0%   0.3516n ± 0%  -24.94% (p=0.000 n=10)
   EncWriteInt/16-bit-lenencoded-10     2.049n ±  0%    2.049n ± 0%        ~ (p=0.972 n=10)
   EncWriteInt/24-bit-lenencoded-10     1.987n ±  0%    2.056n ± 0%   +3.45% (p=0.000 n=10)
   EncWriteInt/32-bit-10               0.7819n ±  0%   0.3906n ± 0%  -50.05% (p=0.000 n=10)
   EncWriteInt/64-bit-10               1.4080n ±  0%   0.4684n ± 0%  -66.73% (p=0.000 n=10)
   EncWriteInt/64-bit-lenencoded-10     3.126n ±  0%    2.051n ± 0%  -34.40% (p=0.000 n=10)
   EncWriteZeroes/4-bytes-10           2.5030n ±  0%   0.3123n ± 0%  -87.52% (p=0.000 n=10)
   EncWriteZeroes/10-bytes-10          4.3815n ±  0%   0.3120n ± 0%  -92.88% (p=0.000 n=10)
   EncWriteZeroes/23-bytes-10          8.4575n ±  0%   0.3124n ± 0%  -96.31% (p=0.000 n=10)
   EncWriteZeroes/55-bytes-10         20.8750n ± 10%   0.6245n ± 0%  -97.01%
   EncReadInt/16-bit-10                 2.050n ±  0%    2.068n ± 1%   +0.90% (p=0.001 n=10)
   EncReadInt/24-bit-10                 2.034n ±  0%    2.050n ± 0%   +0.76% (p=0.000 n=10)
   EncReadInt/64-bit-10                 2.819n ±  1%    2.187n ± 0%  -22.41% (p=0.000 n=10)
   geomean                              2.500n         0.8363n       -66.55%
   ```
   
   Signed-off-by: Matt Robenolt <[email protected]>

   

   mattrobenolt committed Jul 5, 2024
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