mirror of
https://github.com/hasura/graphql-engine.git
synced 2024-12-16 09:51:59 +03:00
cf531b05cb
This PR is on top of #7789. ### Description This PR entirely rewrites the API of the Tracing library, to make `interpTraceT` a thing of the past. Before this change, we ran traces by sticking a `TraceT` on top of whatever we were doing. This had several major drawbacks: - we were carrying a bunch of `TraceT` across the codebase, and the entire codebase had to know about it - we needed to carry a second class constraint around (`HasReporterM`) to be able to run all of those traces - we kept having to do stack rewriting with `interpTraceT`, which went from inconvenient to horrible - we had to declare several behavioral instances on `TraceT m` This PR rewrite all of `Tracing` using a more conventional model: there is ONE `TraceT` at the bottom of the stack, and there is an associated class constraint `MonadTrace`: any part of the code that happens to satisfy `MonadTrace` is able to create new traces. We NEVER have to do stack rewriting, `interpTraceT` is gone, and `TraceT` and `Reporter` become implementation details that 99% of the code is blissfully unaware of: code that needs to do tracing only needs to declare that the monad in which it operates implements `MonadTrace`. In doing so, this PR revealed **several bugs in the codebase**: places where we were expecting to trace something, but due to the default instance of `HasReporterM IO` we would actually not do anything. This PR also splits the code of `Tracing` in more byte-sized modules, with the goal of potentially moving to `server/lib` down the line. ### Remaining work This PR is a draft; what's left to do is: - [x] make Pro compile; i haven't updated `HasuraPro/Main` yet - [x] document Tracing by writing a note that explains how to use the library, and the meaning of "reporter", "trace" and "span", as well as the pitfalls - [x] discuss some of the trade-offs in the implementation, which is why i'm opening this PR already despite it not fully building yet - [x] it depends on #7789 being merged first PR-URL: https://github.com/hasura/graphql-engine-mono/pull/7791 GitOrigin-RevId: cadd32d039134c93ddbf364599a2f4dd988adea8
89 lines
2.8 KiB
Haskell
89 lines
2.8 KiB
Haskell
module Hasura.Tracing.Sampling
|
|
( -- * SamplingState
|
|
SamplingState (..),
|
|
samplingStateToHeader,
|
|
samplingStateFromHeader,
|
|
|
|
-- * SamplingDecision
|
|
SamplingDecision (..),
|
|
|
|
-- * SamplingPolicy
|
|
SamplingPolicy,
|
|
sampleNever,
|
|
sampleAlways,
|
|
sampleRandomly,
|
|
sampleOneInN,
|
|
)
|
|
where
|
|
|
|
import Hasura.Prelude
|
|
import Refined (Positive, Refined, unrefine)
|
|
import System.Random.Stateful qualified as Random
|
|
|
|
--------------------------------------------------------------------------------
|
|
-- SamplingState
|
|
|
|
-- | B3 propagation sampling state.
|
|
--
|
|
-- Debug sampling state not represented.
|
|
data SamplingState = SamplingDefer | SamplingDeny | SamplingAccept
|
|
|
|
-- | Convert a sampling state to a value for the X-B3-Sampled header. A return
|
|
-- value of Nothing indicates that the header should not be set.
|
|
samplingStateToHeader :: IsString s => SamplingState -> Maybe s
|
|
samplingStateToHeader = \case
|
|
SamplingDefer -> Nothing
|
|
SamplingDeny -> Just "0"
|
|
SamplingAccept -> Just "1"
|
|
|
|
-- | Convert a X-B3-Sampled header value to a sampling state. An input of
|
|
-- Nothing indicates that the header was not set.
|
|
samplingStateFromHeader :: (IsString s, Eq s) => Maybe s -> SamplingState
|
|
samplingStateFromHeader = \case
|
|
Nothing -> SamplingDefer
|
|
Just "0" -> SamplingDeny
|
|
Just "1" -> SamplingAccept
|
|
Just _ -> SamplingDefer
|
|
|
|
--------------------------------------------------------------------------------
|
|
-- SamplingDecision
|
|
|
|
-- | A local decision about whether or not to sample spans.
|
|
data SamplingDecision = SampleNever | SampleAlways
|
|
|
|
--------------------------------------------------------------------------------
|
|
-- SamplingPolicy
|
|
|
|
-- | An IO action for deciding whether or not to sample a trace.
|
|
--
|
|
-- Currently restricted to deny access to the B3 sampling state, but we may
|
|
-- want to be more flexible in the future.
|
|
type SamplingPolicy = IO SamplingDecision
|
|
|
|
sampleNever :: SamplingPolicy
|
|
sampleNever = pure SampleNever
|
|
|
|
sampleAlways :: SamplingPolicy
|
|
sampleAlways = pure SampleAlways
|
|
|
|
-- @sampleRandomly p@ returns `SampleAlways` with probability @p@ and
|
|
-- `SampleNever` with probability @1 - p@.
|
|
sampleRandomly :: Double -> SamplingPolicy
|
|
sampleRandomly samplingProbability
|
|
| samplingProbability <= 0 = pure SampleNever
|
|
| samplingProbability >= 1 = pure SampleAlways
|
|
| otherwise = do
|
|
x <- Random.uniformRM (0, 1) Random.globalStdGen
|
|
pure $ if x < samplingProbability then SampleAlways else SampleNever
|
|
|
|
-- Like @sampleRandomly@, but with the probability expressed as the denominator
|
|
-- N of the fraction 1/N.
|
|
sampleOneInN :: Refined Positive Int -> SamplingPolicy
|
|
sampleOneInN denominator
|
|
| n == 1 = pure SampleAlways
|
|
| otherwise = do
|
|
x <- Random.uniformRM (0, n - 1) Random.globalStdGen
|
|
pure $ if x == 0 then SampleAlways else SampleNever
|
|
where
|
|
n = unrefine denominator
|