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PR-URL: https://github.com/hasura/graphql-engine-mono/pull/10218 Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> Co-authored-by: Rob Dominguez <24390149+robertjdominguez@users.noreply.github.com> GitOrigin-RevId: d3dbea6220fd2127ab76c0a240fc4725ca5d6aac
90 lines
2.8 KiB
Haskell
90 lines
2.8 KiB
Haskell
module Hasura.Tracing.Sampling
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( -- * SamplingState
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SamplingState (..),
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samplingStateToHeader,
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samplingStateFromHeader,
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-- * SamplingDecision
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SamplingDecision (..),
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-- * SamplingPolicy
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SamplingPolicy,
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sampleNever,
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sampleAlways,
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sampleRandomly,
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sampleOneInN,
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)
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where
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import Hasura.Prelude
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import Refined (Positive, Refined, unrefine)
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import System.Random.Stateful qualified as Random
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--------------------------------------------------------------------------------
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-- SamplingState
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-- | B3 propagation sampling state.
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--
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-- Debug sampling state not represented.
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data SamplingState = SamplingDefer | SamplingDeny | SamplingAccept
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deriving (Show, Eq)
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-- | Convert a sampling state to a value for the X-B3-Sampled header. A return
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-- value of Nothing indicates that the header should not be set.
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samplingStateToHeader :: (IsString s) => SamplingState -> Maybe s
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samplingStateToHeader = \case
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SamplingDefer -> Nothing
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SamplingDeny -> Just "0"
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SamplingAccept -> Just "1"
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-- | Convert a X-B3-Sampled header value to a sampling state. An input of
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-- Nothing indicates that the header was not set.
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samplingStateFromHeader :: (IsString s, Eq s) => Maybe s -> SamplingState
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samplingStateFromHeader = \case
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Nothing -> SamplingDefer
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Just "0" -> SamplingDeny
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Just "1" -> SamplingAccept
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Just _ -> SamplingDefer
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--------------------------------------------------------------------------------
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-- SamplingDecision
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-- | A local decision about whether or not to sample spans.
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data SamplingDecision = SampleNever | SampleAlways
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--------------------------------------------------------------------------------
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-- SamplingPolicy
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-- | An IO action for deciding whether or not to sample a trace.
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--
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-- Currently restricted to deny access to the B3 sampling state, but we may
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-- want to be more flexible in the future.
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type SamplingPolicy = IO SamplingDecision
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sampleNever :: SamplingPolicy
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sampleNever = pure SampleNever
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sampleAlways :: SamplingPolicy
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sampleAlways = pure SampleAlways
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-- @sampleRandomly p@ returns `SampleAlways` with probability @p@ and
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-- `SampleNever` with probability @1 - p@.
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sampleRandomly :: Double -> SamplingPolicy
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sampleRandomly samplingProbability
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| samplingProbability <= 0 = pure SampleNever
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| samplingProbability >= 1 = pure SampleAlways
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| otherwise = do
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x <- Random.uniformRM (0, 1) Random.globalStdGen
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pure $ if x < samplingProbability then SampleAlways else SampleNever
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-- Like @sampleRandomly@, but with the probability expressed as the denominator
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-- N of the fraction 1/N.
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sampleOneInN :: Refined Positive Int -> SamplingPolicy
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sampleOneInN denominator
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| n == 1 = pure SampleAlways
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| otherwise = do
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x <- Random.uniformRM (0, n - 1) Random.globalStdGen
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pure $ if x == 0 then SampleAlways else SampleNever
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where
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n = unrefine denominator
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