go/vt/sqlparser: improve performance in TrackedBuffer formatting

[mattrobenolt]

Two minor things:

• decently improve formatting integers (%d)
• WriteArg calls buf.Grow to avoid potentially 2 allocations

For integer formatting, buf.WriteString(fmt.Sprintf(...)) was about the worst way to do it. fmt.Sprintf itself allocates a new string, plus it's %d formatting is much more robust in handling padding and whatnot.

First alternative for free win was using fmt.Fprintf(&buf, ...) instead, which simply avoids the extra allocation and just writes directly to the buffer.

But strconv.Format{I,Ui}nt is quite fast, especially since it has a fast path for "small integers".

Here's a trivial benchmark of all 3 options:

$ benchstat fmt.txt
goos: darwin
goarch: arm64
pkg: x
                       │   fmt.txt   │
                       │   sec/op    │
FormatInt/Sprintf-10     55.51n ± 1%
FormatInt/Fprintf-10     50.76n ± 1%
FormatInt/FormatInt-10   17.16n ± 2%
geomean                  36.43n

                       │  fmt.txt   │
                       │    B/op    │
FormatInt/Sprintf-10     16.00 ± 0%
FormatInt/Fprintf-10     8.000 ± 0%
FormatInt/FormatInt-10   8.000 ± 0%
geomean                  10.08

                       │  fmt.txt   │
                       │ allocs/op  │
FormatInt/Sprintf-10     2.000 ± 0%
FormatInt/Fprintf-10     1.000 ± 0%
FormatInt/FormatInt-10   1.000 ± 0%
geomean                  1.260

So each %d within a format string is considerably faster. This obviously scales linearly with the number of %d's there are.

Related Issue(s)

Part of #16789

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[mattrobenolt]

As a potential follow up:

I got here because WriteArg stood out a bit in a pprof I was looking at for heap allocations, and the other thing that can be done in here with some more work is the bindLocations slice that keeps getting appended to 1 at a time.

So we might want to do a thing where we count up the args first so can we grow the slice, then append to the slice. So adding a method like, GrowArgs(size)

[codecov]

Codecov Report

Attention: Patch coverage is 93.75000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 68.92%. Comparing base (6fc808d) to head (57b4035).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/sqlparser/tracked_buffer.go	93.75%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16364   +/-   ##
=======================================
  Coverage   68.91%   68.92%           
=======================================
  Files        1566     1566           
  Lines      201855   201885   +30     
=======================================
+ Hits       139113   139147   +34     
+ Misses      62742    62738    -4     

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[deepthi]

@mattrobenolt would you mind creating an umbrella issue like "VTGate performance improvements" or something similar and referring to that in this series of PRs?

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[vmg]

Note that this is still allocating memory when the small-number optimization doesn't trigger, so that isn't great. I think it may be time to leave behind the *strings.Builder used here and instead implementing building ourselves, which would allow us to simplify many things, including using strconv.AppendInt instead of the Format versions. Maybe for another PR!

[mattrobenolt]

Yeah, I assume you're thinking something more specialized like what zap does? https://github.com/uber-go/zap/blob/master/buffer/buffer.go