The difference is modest, but we've used `slices.Sort` in lots of other
places so why not here.
name old time/op new time/op delta
Builder 1.04µs ± 3% 0.95µs ± 3% -8.27% (p=0.008 n=5+5)
name old alloc/op new alloc/op delta
Builder 312B ± 0% 288B ± 0% -7.69% (p=0.008 n=5+5)
name old allocs/op new allocs/op delta
Builder 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5)
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
This makes the buffer the correct size for the common case that labels
have only been added. It will be too large for the case that labels are
changed, but the current buffer resize logic in `appendLabelTo` doubles
the buffer, so a small over-estimate is better.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
This commit adds an alternate implementation for `labels.Labels`, behind
a build tag `stringlabels`.
Instead of storing label names and values as individual strings, they
are all concatenated into one string in this format:
[len][name0][len][value0][len][name1][len][value1]...
The lengths are varint encoded so usually a single byte.
The previous `[]string` had 24 bytes of overhead for the slice and 16
for each label name and value; this one has 16 bytes overhead plus 1
for each name and value.
In `ScratchBuilder.Overwrite` and `Labels.Hash` we use an unsafe
conversion from string to byte slice. `Overwrite` is explicitly unsafe,
but for `Hash` this is a pure performance hack.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
