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chore(sampling): track knuth sampling in distributed trace #14425

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7608c6b
chore(sampling): track kneuth sampling in distributed trace
mabdinur Aug 26, 2025
e680ed5
update snapshot tests
mabdinur Aug 26, 2025
4ae1614
fix typo
mabdinur Aug 26, 2025
107383f
only set rate for ss, trace sampling, and priority sampling
mabdinur Aug 26, 2025
66d3ba8
fix snapshot
mabdinur Aug 26, 2025
ffab3d4
Merge branch 'main' into munir/track-sampling-ksr
brettlangdon Aug 26, 2025
eba4f14
ensure ksr is always in metrics
mabdinur Aug 29, 2025
c1139b9
Merge branch 'main' into munir/track-sampling-ksr
mabdinur Sep 2, 2025
30af517
simplify to meet current spec
mabdinur Sep 3, 2025
8e4bc88
missed comment
mabdinur Sep 3, 2025
5e95d62
update snapshots
mabdinur Sep 4, 2025
7d634e3
revert changes
mabdinur Sep 4, 2025
04335cb
fix testagent tests
mabdinur Sep 5, 2025
05a1e83
Merge branch 'main' into munir/track-sampling-ksr
mabdinur Sep 5, 2025
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1 change: 1 addition & 0 deletions ddtrace/internal/constants.py
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Expand Up @@ -22,6 +22,7 @@
_PROPAGATION_BEHAVIOR_CONTINUE = "continue"
_PROPAGATION_BEHAVIOR_IGNORE = "ignore"
_PROPAGATION_BEHAVIOR_RESTART = "restart"
KNUTH_SAMPLE_RATE_KEY = "_dd.p.ksr"
_PROPAGATION_BEHAVIOR_DEFAULT = _PROPAGATION_BEHAVIOR_CONTINUE
W3C_TRACESTATE_KEY = "tracestate"
W3C_TRACEPARENT_KEY = "traceparent"
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3 changes: 3 additions & 0 deletions ddtrace/internal/sampling.py
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Expand Up @@ -15,6 +15,7 @@
from ddtrace.constants import _SINGLE_SPAN_SAMPLING_RATE
from ddtrace.internal.constants import _KEEP_PRIORITY_INDEX
from ddtrace.internal.constants import _REJECT_PRIORITY_INDEX
from ddtrace.internal.constants import KNUTH_SAMPLE_RATE_KEY
from ddtrace.internal.constants import MAX_UINT_64BITS
from ddtrace.internal.constants import SAMPLING_DECISION_TRACE_TAG_KEY
from ddtrace.internal.constants import SAMPLING_HASH_MODULO
Expand Down Expand Up @@ -244,8 +245,10 @@ def _set_sampling_tags(span: Span, sampled: bool, sample_rate: float, mechanism:
SamplingMechanism.REMOTE_DYNAMIC_TRACE_SAMPLING_RULE,
):
span.set_metric(_SAMPLING_RULE_DECISION, sample_rate)
span.set_tag_str(KNUTH_SAMPLE_RATE_KEY, f"{sample_rate:.6g}")
elif mechanism == SamplingMechanism.AGENT_RATE_BY_SERVICE:
span.set_metric(_SAMPLING_AGENT_DECISION, sample_rate)
span.set_tag_str(KNUTH_SAMPLE_RATE_KEY, f"{sample_rate:.6g}")
# Set the sampling priority
priorities = SAMPLING_MECHANISM_TO_PRIORITIES[mechanism]
priority_index = _KEEP_PRIORITY_INDEX if sampled else _REJECT_PRIORITY_INDEX
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7 changes: 3 additions & 4 deletions ddtrace/propagation/http.py
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Expand Up @@ -17,7 +17,7 @@
from ddtrace._trace.span import Span # noqa:F401
from ddtrace._trace.span import _get_64_highest_order_bits_as_hex
from ddtrace._trace.span import _get_64_lowest_order_bits_as_int
from ddtrace._trace.span import _MetaDictType
from ddtrace._trace.types import _MetaDictType
from ddtrace.appsec._constants import APPSEC
from ddtrace.internal import core
from ddtrace.internal.telemetry import telemetry_writer
Expand Down Expand Up @@ -220,7 +220,7 @@ def _extract_meta(tags_value):
meta = {
"_dd.propagation_error": "extract_max_size",
}
log.warning("failed to decode x-datadog-tags", exc_info=True)
log.warning("failed to decode x-datadog-tags: %r", tags_value, exc_info=True)
except TagsetDecodeError:
meta = {
"_dd.propagation_error": "decoding_error",
Expand Down Expand Up @@ -360,7 +360,6 @@ def _extract(headers):

if not meta:
meta = {}

# Try to parse values into their expected types
try:
if sampling_priority is not None:
Expand Down Expand Up @@ -672,7 +671,7 @@ class _TraceContext:
The format for ``tracestate`` is key value pairs with each entry limited to 256 characters.
An example of the ``dd`` list member we would add is::
"dd=s:2;o:rum;t.dm:-4;t.usr.id:baz64"
"dd=s:2;o:rum;t.dm:-4;t.usr.id:baz64;t.ksr:0.0001"
Implementation details:
- Datadog Trace and Span IDs are 64-bit unsigned integers.
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1 change: 1 addition & 0 deletions tests/snapshots/test_sampling_with_default_sample_rate_1.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "1",
"language": "python",
"runtime-id": "10b45fb36ca3465fa2b6dbd7b10bdccf"
},
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1 change: 1 addition & 0 deletions tests/snapshots/test_sampling_with_default_sample_rate_1_and_rule_1.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "1",
"language": "python",
"runtime-id": "10b45fb36ca3465fa2b6dbd7b10bdccf"
},
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1 change: 1 addition & 0 deletions tests/snapshots/test_sampling_with_default_sample_rate_tiny.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "1.0000001",
"language": "python",
"runtime-id": "10b45fb36ca3465fa2b6dbd7b10bdccf"
},
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1 change: 1 addition & 0 deletions tests/snapshots/test_sampling_with_sample_rate_1_and_rate_limit_0.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "1",
"language": "python",
"runtime-id": "9d1cfdf7026e45dea46fc4c83768cc7b"
},
Expand Down
1 change: 1 addition & 0 deletions tests/snapshots/test_sampling_with_sample_rate_1_and_rate_limit_3_and_rule_0.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"language": "python",
"runtime-id": "9d1cfdf7026e45dea46fc4c83768cc7b"
},
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6 changes: 6 additions & 0 deletions tests/snapshots/tests.integration.test_integration_snapshots.test_sampling.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-4",
"_dd.p.ksr": "1",
"language": "python",
"runtime-id": "6f2eeb0b30c54268b96f6eca8a2d66ba"
},
Expand Down Expand Up @@ -46,6 +47,7 @@
"type": "",
"error": 0,
"meta": {
"_dd.p.ksr": "1",
"language": "python",
"runtime-id": "6f2eeb0b30c54268b96f6eca8a2d66ba"
},
Expand Down Expand Up @@ -82,6 +84,7 @@
"type": "",
"error": 0,
"meta": {
"_dd.p.ksr": "0",
"language": "python",
"runtime-id": "6f2eeb0b30c54268b96f6eca8a2d66ba"
},
Expand Down Expand Up @@ -119,6 +122,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "1",
"language": "python",
"runtime-id": "6f2eeb0b30c54268b96f6eca8a2d66ba"
},
Expand Down Expand Up @@ -155,6 +159,7 @@
"type": "",
"error": 0,
"meta": {
"_dd.p.ksr": "0.000001",
"language": "python",
"runtime-id": "6f2eeb0b30c54268b96f6eca8a2d66ba"
},
Expand Down Expand Up @@ -192,6 +197,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "1",
"language": "python",
"runtime-id": "6f2eeb0b30c54268b96f6eca8a2d66ba"
},
Expand Down
1 change: 1 addition & 0 deletions tests/snapshots/tests.integration.test_priority_sampling.test_agent_sample_rate_keep.json
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Expand Up @@ -11,6 +11,7 @@
"meta": {
"_dd.base_service": "tests.integration",
"_dd.p.dm": "-1",
"_dd.p.ksr": "0.9999",
"_dd.p.tid": "656a1a2b00000000",
"language": "python",
"runtime-id": "701521214f1f4473abe1afca4813fbec"
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1 change: 1 addition & 0 deletions tests/snapshots/tests.integration.test_priority_sampling.test_agent_sample_rate_reject.json
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Expand Up @@ -11,6 +11,7 @@
"meta": {
"_dd.base_service": "tests.integration",
"_dd.p.dm": "-1",
"_dd.p.ksr": "0.0001",
"_dd.p.tid": "656a1a2b00000000",
"language": "python",
"runtime-id": "701521214f1f4473abe1afca4813fbec"
Expand Down
3 changes: 3 additions & 0 deletions ...tests.integration.test_sampling.test_extended_sampling_float_special_case_match_star.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "68824df100000000",
"language": "python",
"runtime-id": "79453d6c5643438bbdf8e2c1d9548877"
Expand Down Expand Up @@ -37,6 +38,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "68824df100000000",
"language": "python",
"runtime-id": "79453d6c5643438bbdf8e2c1d9548877"
Expand Down Expand Up @@ -64,6 +66,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "68824df100000000",
"language": "python",
"runtime-id": "79453d6c5643438bbdf8e2c1d9548877"
Expand Down
1 change: 1 addition & 0 deletions tests/snapshots/tests.integration.test_sampling.test_extended_sampling_glob_multi_rule.json
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Expand Up @@ -11,6 +11,7 @@
"meta": {
"_dd.base_service": "ddtrace_subprocess_dir",
"_dd.p.dm": "-3",
"_dd.p.ksr": "1",
"_dd.p.tid": "65cd344600000000",
"language": "python",
"runtime-id": "9356e035b52344f6b4a7227820d797d5",
Expand Down
1 change: 1 addition & 0 deletions tests/snapshots/tests.integration.test_sampling.test_extended_sampling_resource.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"language": "python",
"runtime-id": "7871c85140a0460c939f2c0fe8153f65"
},
Expand Down
1 change: 1 addition & 0 deletions .../snapshots/tests.integration.test_sampling.test_extended_sampling_string_sample_rate.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "68828b2100000000",
"language": "python",
"runtime-id": "992ed589103d4826839b0d6ec8b5766f"
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1 change: 1 addition & 0 deletions tests/snapshots/tests.integration.test_sampling.test_extended_sampling_tags.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"language": "python",
"runtime-id": "c7c739442f864f07b02918014eb23b3a",
"tag1": "mycooltag"
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1 change: 1 addition & 0 deletions .../snapshots/tests.integration.test_sampling.test_extended_sampling_tags_and_name_glob.json
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Expand Up @@ -88,6 +88,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65ca9a0600000000",
"language": "python",
"runtime-id": "45b9ec5ab8354bbcafce88b29abcb7a4",
Expand Down
1 change: 1 addition & 0 deletions ...s/snapshots/tests.integration.test_sampling.test_extended_sampling_tags_and_resource.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"language": "python",
"runtime-id": "c7c739442f864f07b02918014eb23b3a",
"tag1": "mycooltag"
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1 change: 1 addition & 0 deletions ...pshots/tests.integration.test_sampling.test_extended_sampling_tags_and_resource_glob.json
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Expand Up @@ -88,6 +88,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65ca9a0600000000",
"language": "python",
"runtime-id": "45b9ec5ab8354bbcafce88b29abcb7a4",
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1 change: 1 addition & 0 deletions ...apshots/tests.integration.test_sampling.test_extended_sampling_tags_and_service_glob.json
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Expand Up @@ -90,6 +90,7 @@
"meta": {
"_dd.base_service": "ddtrace_subprocess_dir",
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cbae1700000000",
"language": "python",
"runtime-id": "ddb451e9ba4245cc915e8914d4f8c008",
Expand Down
1 change: 1 addition & 0 deletions tests/snapshots/tests.integration.test_sampling.test_extended_sampling_tags_glob.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"language": "python",
"runtime-id": "c3c5d61c08d04b488d7b54ebe541d3be",
"tag1": "mycooltag"
Expand Down
1 change: 1 addition & 0 deletions ...ts.integration.test_sampling.test_extended_sampling_tags_glob_insensitive_case_match.json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cbe3ad00000000",
"language": "python",
"runtime-id": "4ef91661e8454c5e9b76221f1d77592e",
Expand Down
1 change: 1 addition & 0 deletions .../snapshots/tests.integration.test_sampling.test_extended_sampling_tags_partial_match.json
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Expand Up @@ -38,6 +38,7 @@
"meta": {
"_dd.base_service": "ddtrace_subprocess_dir",
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "6881b20100000000",
"language": "python",
"runtime-id": "e5827348f1274e43a58dc88d9dc65596",
Expand Down
2 changes: 2 additions & 0 deletions tests/snapshots/tests.integration.test_sampling.test_extended_sampling_w_None.json
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Expand Up @@ -36,6 +36,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cce0ee00000000",
"language": "python",
"runtime-id": "07be192aacd94df1a67482ebde627263",
Expand Down Expand Up @@ -63,6 +64,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cce0ee00000000",
"language": "python",
"runtime-id": "07be192aacd94df1a67482ebde627263",
Expand Down
2 changes: 2 additions & 0 deletions tests/snapshots/tests.integration.test_sampling.test_extended_sampling_w_None_meta.json
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Expand Up @@ -36,6 +36,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cd05a600000000",
"language": "python",
"runtime-id": "ab78d1d0e61246e1b417857c4ea49171",
Expand Down Expand Up @@ -63,6 +64,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cd05a600000000",
"language": "python",
"runtime-id": "ab78d1d0e61246e1b417857c4ea49171",
Expand Down
2 changes: 2 additions & 0 deletions tests/snapshots/tests.integration.test_sampling.test_extended_sampling_w_metrics.json
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Expand Up @@ -36,6 +36,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cd193b00000000",
"language": "python",
"runtime-id": "1627de339aa344188313503df35b1373",
Expand Down Expand Up @@ -63,6 +64,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cd193b00000000",
"language": "python",
"runtime-id": "1627de339aa344188313503df35b1373"
Expand Down
2 changes: 2 additions & 0 deletions tests/snapshots/tests.integration.test_sampling.test_extended_sampling_w_tags_none.json
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Expand Up @@ -36,6 +36,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cd193b00000000",
"language": "python",
"runtime-id": "1627de339aa344188313503df35b1373",
Expand Down Expand Up @@ -63,6 +64,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "65cd193b00000000",
"language": "python",
"runtime-id": "1627de339aa344188313503df35b1373",
Expand Down
1 change: 1 addition & 0 deletions ...gration.test_sampling.test_single_span_and_trace_sampling_match_non_root_span[false].json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "68a5d4f600000000",
"language": "python",
"runtime-id": "bd82a94572fa42f3b93b6c15e1cce2b0"
Expand Down
1 change: 1 addition & 0 deletions ...sampling.test_single_span_and_trace_sampling_match_root_span_paritial_flushing[true].json
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Expand Up @@ -10,6 +10,7 @@
"error": 0,
"meta": {
"_dd.p.dm": "-3",
"_dd.p.ksr": "0",
"_dd.p.tid": "68a5d77c00000000",
"language": "python",
"runtime-id": "a94ba981c47e47afada25a6e6e152765"
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1 change: 1 addition & 0 deletions ...apshots/tests.integration.test_trace_stats.test_single_span_sampling[sampling_rule1].json
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Expand Up @@ -11,6 +11,7 @@
"meta": {
"_dd.base_service": "tests.integration",
"_dd.p.dm": "-3",
"_dd.p.ksr": "1",
"_dd.p.tid": "6670641f00000000",
"language": "python",
"runtime-id": "423178dbb29d4ca784743ac73e5678c8"
Expand Down
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