distributor: more efficient labels error messages

[bboreham]

What this PR does

This is split into three commits:

• Changing getMetricAndEllipsis - instead of converting to Labels then to a map then to a string,
  we use nearby function formatLabelSet which avoids the first two conversions.
  Some tests need to be fixed up, because prometheus/common is sorting labels incorrectly.
• Re-code formatLabelSet to remove intermediate string slice and two uses of Sprintf.
• Tweak one of the benchmarks, to use a more reasonable test case. 2KB is so long it distorts benchmark timings.

goos: darwin
goarch: arm64
pkg: github.com/grafana/mimir/pkg/distributor
                                                            │    before    │               after                │
                                                            │    sec/op    │   sec/op     vs base               │
Distributor_Push/too_many_labels_limit_reached-8              11.067m ± 2%   3.450m ± 0%  -68.83% (p=0.002 n=6)
Distributor_Push/max_label_name_length_limit_reached-8         3.096m ± 1%   1.937m ± 1%  -37.42% (p=0.002 n=6)
Distributor_Push/max_label_value_length_limit_reached-8        4.244m ± 0%   3.051m ± 2%  -28.11% (p=0.002 n=6)
Distributor_Push/timestamp_too_new-8                           623.5µ ± 1%   623.7µ ± 2%        ~ (p=0.589 n=6)
Distributor_Push/all_samples_go_to_metric_relabel_configs-8    1.388m ± 2%   1.376m ± 1%        ~ (p=0.394 n=6)
Distributor_Push/all_samples_successfully_pushed-8             652.9µ ± 1%   644.7µ ± 1%   -1.26% (p=0.002 n=6)
Distributor_Push/ingestion_rate_limit_reached-8                302.7µ ± 1%   297.4µ ± 2%   -1.75% (p=0.041 n=6)
geomean                                                        1.583m        1.189m       -24.89%

                                                            │    before    │                after                 │
                                                            │     B/op     │     B/op       vs base               │
Distributor_Push/too_many_labels_limit_reached-8              7.723Mi ± 0%   1.177Mi ±  0%  -84.77% (p=0.002 n=6)
Distributor_Push/max_label_name_length_limit_reached-8        2.436Mi ± 0%   1.117Mi ±  0%  -54.13% (p=0.002 n=6)
Distributor_Push/max_label_value_length_limit_reached-8       2.697Mi ± 0%   1.178Mi ±  0%  -56.31% (p=0.002 n=6)
Distributor_Push/timestamp_too_new-8                          348.9Ki ± 0%   349.2Ki ±  0%   +0.08% (p=0.009 n=6)
Distributor_Push/all_samples_go_to_metric_relabel_configs-8   233.7Ki ± 0%   233.4Ki ±  1%        ~ (p=0.394 n=6)
Distributor_Push/all_samples_successfully_pushed-8            152.0Ki ± 0%   152.2Ki ±  0%        ~ (p=0.240 n=6)
Distributor_Push/ingestion_rate_limit_reached-8               2.140Ki ± 1%   2.126Ki ± 11%        ~ (p=0.833 n=6)
geomean                                                       392.8Ki        238.5Ki        -39.30%

                                                            │    before     │               after                │
                                                            │   allocs/op   │  allocs/op   vs base               │
Distributor_Push/too_many_labels_limit_reached-8              108.181k ± 0%   6.046k ± 0%  -94.41% (p=0.002 n=6)
Distributor_Push/max_label_name_length_limit_reached-8         43.052k ± 0%   6.047k ± 0%  -85.95% (p=0.002 n=6)
Distributor_Push/max_label_value_length_limit_reached-8        44.053k ± 0%   6.047k ± 0%  -86.27% (p=0.002 n=6)
Distributor_Push/timestamp_too_new-8                            5.043k ± 0%   5.043k ± 0%        ~ (p=1.000 n=6)
Distributor_Push/all_samples_go_to_metric_relabel_configs-8     5.057k ± 0%   5.057k ± 0%        ~ (p=1.000 n=6)
Distributor_Push/all_samples_successfully_pushed-8               54.00 ± 2%    54.00 ± 2%        ~ (p=1.000 n=6)
Distributor_Push/ingestion_rate_limit_reached-8                  34.00 ± 0%    34.00 ± 3%        ~ (p=1.000 n=6)
geomean                                                         3.706k        1.396k       -62.32%

Checklist

• Tests updated.
• NA Documentation added.
• CHANGELOG.md updated

[56quarters]

Nicely done!

[jhalterman]

LGTM

Somewhat tangential, but I wonder if formatLabelSet should be moved to the mimirpb package since it seems generally useful for []LabelAdapter.

[bboreham]

Somewhat tangential, but I wonder if formatLabelSet should be moved to the mimirpb package since it seems generally useful for []LabelAdapter.

Definitely seems reasonable.

[bboreham]

Move to mimirpb and call it from more places in #6822