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WIP: optimize sample unmarshaling for json/v2 - #991

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liggitt:json-v2-unmarshal
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WIP: optimize sample unmarshaling for json/v2#991
liggitt wants to merge 7 commits into
prometheus:mainfrom
liggitt:json-v2-unmarshal

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@liggitt liggitt commented Sep 20, 2026 •
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Part of prometheus/client_golang#2105

  • Adds UnmarshalJSONFrom optimized streaming unmarshal implementations
  • Implementations are in build-tagged Go 1.27 files, previous version of Go still use less efficient unmarshalers
  • Adds a copy of the sample unmarshaling benchmark from client_golang
  • Adds unit tests to check parity between UnmarshalJSON and UnmarshalJSONFrom implementations
  • TMP: includes commits with benchmark output on go 1.26 and go 1.27 at each step, will drop those before merge

Go 1.27 performance is significantly improved:

benchstat 1-go1.27 3-go1.27 
goos: darwin
goarch: arm64
pkg: github.com/prometheus/common/model
cpu: Apple M4 Pro
                                                            │  1-go1.27   │              3-go1.27              │
                                                            │   sec/op    │   sec/op     vs base               │
SamplesJSONUnmarshal/series=10/dp=10/type=floats-14           56.57µ ± 2%   15.17µ ± 3%  -73.18% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=10/type=histograms-14       538.6µ ± 1%   252.9µ ± 1%  -53.04% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=floats-14          499.9µ ± 0%   106.1µ ± 4%  -78.78% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=histograms-14      5.379m ± 1%   2.491m ± 1%  -53.68% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=floats-14         5.015m ± 1%   1.029m ± 1%  -79.48% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=histograms-14     54.06m ± 1%   25.23m ± 1%  -53.32% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=floats-14          571.9µ ± 1%   148.8µ ± 1%  -73.98% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=histograms-14      5.478m ± 1%   2.547m ± 5%  -53.50% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=floats-14         5.132m ± 1%   1.127m ± 2%  -78.05% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=histograms-14     54.76m ± 1%   26.00m ± 3%  -52.53% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=floats-14        50.94m ± 1%   11.03m ± 2%  -78.34% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=histograms-14    551.0m ± 1%   267.8m ± 3%  -51.39% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=floats-14         5.744m ± 1%   1.604m ± 4%  -72.07% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=histograms-14     55.89m ± 1%   26.66m ± 4%  -52.30% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=floats-14        51.48m ± 1%   11.36m ± 2%  -77.94% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=histograms-14    557.5m ± 1%   266.1m ± 3%  -52.27% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=floats-14       511.5m ± 1%   112.4m ± 3%  -78.02% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=histograms-14    5.584 ± 1%    2.638 ± 1%  -52.75% (p=0.002 n=6)
geomean                                                       17.03m        5.638m       -66.89%

                                                            │   1-go1.27    │              3-go1.27               │
                                                            │     B/op      │     B/op      vs base               │
SamplesJSONUnmarshal/series=10/dp=10/type=floats-14           14.816Ki ± 0%   9.490Ki ± 0%  -35.95% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=10/type=histograms-14       122.76Ki ± 0%   44.67Ki ± 0%  -63.61% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=floats-14           92.10Ki ± 0%   44.52Ki ± 0%  -51.67% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=histograms-14      1175.4Ki ± 0%   400.1Ki ± 0%  -65.96% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=floats-14          967.2Ki ± 0%   497.2Ki ± 0%  -48.59% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=histograms-14     11.335Mi ± 0%   3.775Mi ± 0%  -66.70% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=floats-14          147.68Ki ± 0%   94.40Ki ± 0%  -36.08% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=histograms-14      1227.3Ki ± 0%   446.2Ki ± 0%  -63.64% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=floats-14          920.1Ki ± 0%   444.5Ki ± 0%  -51.69% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=histograms-14     11.471Mi ± 0%   3.905Mi ± 0%  -65.95% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=floats-14         9.438Mi ± 0%   4.853Mi ± 0%  -48.58% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=histograms-14    113.28Mi ± 0%   37.74Mi ± 0%  -66.69% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=floats-14         1471.7Ki ± 0%   939.6Ki ± 0%  -36.16% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=histograms-14     11.973Mi ± 0%   4.352Mi ± 0%  -63.65% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=floats-14         8.975Mi ± 0%   4.335Mi ± 0%  -51.69% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=histograms-14    114.63Mi ± 0%   39.04Mi ± 0%  -65.95% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=floats-14        94.37Mi ± 0%   48.53Mi ± 0%  -48.58% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=histograms-14   1132.7Mi ± 0%   377.3Mi ± 0%  -66.69% (p=0.002 n=6)
geomean                                                        3.521Mi        1.523Mi       -56.74%

                                                            │   1-go1.27    │              3-go1.27              │
                                                            │   allocs/op   │  allocs/op   vs base               │
SamplesJSONUnmarshal/series=10/dp=10/type=floats-14              426.0 ± 0%    116.0 ± 0%  -72.77% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=10/type=histograms-14         5.226k ± 0%   1.216k ± 0%  -76.73% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=floats-14            3156.0 ± 0%    146.0 ± 0%  -95.37% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=histograms-14        51.16k ± 0%   11.15k ± 0%  -78.21% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=floats-14          30197.0 ± 0%    186.0 ± 0%  -99.38% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=histograms-14       510.2k ± 0%   110.2k ± 0%  -78.41% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=floats-14            4.209k ± 0%   1.109k ± 0%  -73.65% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=histograms-14        52.21k ± 0%   12.11k ± 0%  -76.81% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=floats-14          31.510k ± 0%   1.409k ± 0%  -95.53% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=histograms-14       511.5k ± 0%   111.4k ± 0%  -78.22% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=floats-14        301.911k ± 0%   1.809k ± 0%  -99.40% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=histograms-14      5.102M ± 0%   1.102M ± 0%  -78.41% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=floats-14           42.03k ± 0%   11.03k ± 0%  -73.76% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=histograms-14       522.1k ± 0%   121.0k ± 0%  -76.82% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=floats-14         315.03k ± 0%   14.03k ± 0%  -95.55% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=histograms-14      5.115M ± 0%   1.114M ± 0%  -78.22% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=floats-14       3019.04k ± 0%   18.03k ± 0%  -99.40% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=histograms-14     51.02M ± 0%   11.02M ± 0%  -78.41% (p=0.002 n=6)
geomean                                                         132.8k        12.77k       -90.38%

Go 1.26 CPU performance is slightly improved by dropping an unnecessary custom UnmarshalJSON method:

benchstat 1-go1.26 3-go1.26 
goos: darwin
goarch: arm64
pkg: github.com/prometheus/common/model
cpu: Apple M4 Pro
                                                            │   1-go1.26   │              3-go1.26              │
                                                            │    sec/op    │   sec/op     vs base               │
SamplesJSONUnmarshal/series=10/dp=10/type=floats-14           59.13µ ±  3%   44.60µ ± 3%  -24.58% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=10/type=histograms-14       760.4µ ±  1%   586.7µ ± 0%  -22.84% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=floats-14          476.0µ ±  4%   382.1µ ± 1%  -19.73% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=histograms-14      7.449m ±  1%   5.880m ± 1%  -21.07% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=floats-14         4.698m ±  1%   3.799m ± 2%  -19.13% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=histograms-14     76.79m ±  3%   59.98m ± 1%  -21.89% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=floats-14          586.1µ ±  2%   451.7µ ± 1%  -22.94% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=histograms-14      7.550m ±  1%   5.947m ± 0%  -21.22% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=floats-14         4.714m ±  0%   3.855m ± 2%  -18.22% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=histograms-14     75.83m ±  1%   59.81m ± 0%  -21.14% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=floats-14        47.63m ±  3%   38.68m ± 3%  -18.80% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=histograms-14    839.1m ± 43%   617.9m ± 0%  -26.36% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=floats-14         6.479m ± 11%   4.566m ± 1%  -29.53% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=histograms-14     81.97m ±  2%   60.11m ± 1%  -26.67% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=floats-14        51.16m ±  2%   39.35m ± 1%  -23.10% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=histograms-14    804.5m ±  1%   619.6m ± 1%  -22.98% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=floats-14       478.6m ±  2%   394.4m ± 1%  -17.59% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=histograms-14    7.861 ±  2%    6.218 ± 1%  -20.89% (p=0.002 n=6)
geomean                                                       20.15m         15.67m       -22.21%

                                                            │   1-go1.26   │              3-go1.26               │
                                                            │     B/op     │     B/op      vs base               │
SamplesJSONUnmarshal/series=10/dp=10/type=floats-14           31.16Ki ± 0%   28.02Ki ± 0%  -10.08% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=10/type=histograms-14       220.9Ki ± 0%   217.1Ki ± 0%   -1.71% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=floats-14          227.9Ki ± 0%   224.7Ki ± 0%   -1.38% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=histograms-14      2.073Mi ± 0%   2.070Mi ± 0%   -0.18% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=floats-14         2.244Mi ± 0%   2.241Mi ± 0%   -0.14% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=histograms-14     20.56Mi ± 0%   20.56Mi ± 0%   -0.02% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=floats-14          309.4Ki ± 0%   277.4Ki ± 0%  -10.33% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=histograms-14      2.155Mi ± 0%   2.117Mi ± 0%   -1.73% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=floats-14         2.223Mi ± 0%   2.192Mi ± 0%   -1.40% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=histograms-14     20.73Mi ± 0%   20.69Mi ± 0%   -0.18% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=floats-14        22.43Mi ± 0%   22.40Mi ± 0%   -0.14% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=histograms-14    205.6Mi ± 0%   205.6Mi ± 0%   -0.02% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=floats-14         3.015Mi ± 0%   2.703Mi ± 0%  -10.37% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=histograms-14     21.54Mi ± 0%   21.17Mi ± 0%   -1.74% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=floats-14        22.23Mi ± 0%   21.91Mi ± 0%   -1.41% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=histograms-14    207.3Mi ± 0%   206.9Mi ± 0%   -0.18% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=floats-14       224.3Mi ± 0%   224.0Mi ± 0%   -0.14% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=histograms-14   2.008Gi ± 0%   2.008Gi ± 0%   -0.02% (p=0.002 n=6)
geomean                                                       7.195Mi        7.025Mi        -2.36%

                                                            │  1-go1.26   │              3-go1.26              │
                                                            │  allocs/op  │  allocs/op   vs base               │
SamplesJSONUnmarshal/series=10/dp=10/type=floats-14            530.0 ± 0%    462.0 ± 0%  -12.83% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=10/type=histograms-14       4.541k ± 0%   4.463k ± 0%   -1.72% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=floats-14          3.260k ± 0%   3.192k ± 0%   -2.09% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=100/type=histograms-14      43.27k ± 0%   43.19k ± 0%   -0.18% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=floats-14         30.30k ± 0%   30.23k ± 0%   -0.22% (p=0.002 n=6)
SamplesJSONUnmarshal/series=10/dp=1000/type=histograms-14     430.3k ± 0%   430.2k ± 0%   -0.02% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=floats-14          5.213k ± 0%   4.515k ± 0%  -13.39% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=10/type=histograms-14      45.31k ± 0%   44.52k ± 0%   -1.76% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=floats-14         32.51k ± 0%   31.82k ± 0%   -2.15% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=100/type=histograms-14     432.6k ± 0%   431.8k ± 0%   -0.18% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=floats-14        302.9k ± 0%   302.2k ± 0%   -0.23% (p=0.002 n=6)
SamplesJSONUnmarshal/series=100/dp=1000/type=histograms-14    4.303M ± 0%   4.302M ± 0%   -0.02% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=floats-14         52.02k ± 0%   45.02k ± 0%  -13.45% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=10/type=histograms-14     453.0k ± 0%   445.0k ± 0%   -1.77% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=floats-14        325.0k ± 0%   318.0k ± 0%   -2.15% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=100/type=histograms-14    4.326M ± 0%   4.318M ± 0%   -0.18% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=floats-14       3.029M ± 0%   3.022M ± 0%   -0.23% (p=0.002 n=6)
SamplesJSONUnmarshal/series=1000/dp=1000/type=histograms-14   43.03M ± 0%   43.02M ± 0%   -0.02% (p=0.002 n=6)
geomean                                                       127.8k        123.9k        -3.04%

cc @bwplotka

@liggitt
Add json v1/v2, round-trip, and sample unmarshal benchmark tests
07f488c 
Signed-off-by: Jordan Liggitt <liggitt@google.com>
@liggitt
TMP: benchmark 1
e73ffef 
Signed-off-by: Jordan Liggitt <liggitt@google.com>
@liggitt
Drop unnecessary custom UnmarshalJSON
a39ac7b 
5-20% CPU improvement
0-12% alloc/memory improvement

Signed-off-by: Jordan Liggitt <liggitt@google.com>
@liggitt
TMP: benchmark 2
94281fd 
Signed-off-by: Jordan Liggitt <liggitt@google.com>
@liggitt
SamplePair#UnmarshalJSONFrom
28e8398 
Signed-off-by: Jordan Liggitt <liggitt@google.com>
@liggitt
histogram UnmarshalJSONFrom implementations
0d86d7a 
Signed-off-by: Jordan Liggitt <liggitt@google.com>
@liggitt
TMP: benchmark 3
68760d9 
Signed-off-by: Jordan Liggitt <liggitt@google.com>
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