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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
38 lines
1.2 KiB
Haskell
38 lines
1.2 KiB
Haskell
module Hasura.Tracing.Context
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( TraceContext (..),
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TraceMetadata,
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)
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where
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import Data.Aeson ((.=))
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import Data.Aeson qualified as J
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import Hasura.Prelude
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import Hasura.Tracing.Sampling
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import Hasura.Tracing.TraceId
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-- | Any additional human-readable key-value pairs relevant
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-- to the execution of a block of code.
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type TraceMetadata = [(Text, Text)]
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-- | A trace context records the current active trace, the active span
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-- within that trace, and the span's parent, unless the current span
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-- is the root.
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data TraceContext = TraceContext
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{ tcCurrentTrace :: TraceId,
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tcCurrentSpan :: SpanId,
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tcCurrentParent :: Maybe SpanId,
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tcSamplingState :: SamplingState
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}
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-- Should this be here? This implicitly ties Tracing to the name of fields in HTTP headers.
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instance J.ToJSON TraceContext where
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toJSON TraceContext {..} =
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let idFields =
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[ "trace_id" .= bsToTxt (traceIdToHex tcCurrentTrace),
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"span_id" .= bsToTxt (spanIdToHex tcCurrentSpan)
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]
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samplingFieldMaybe =
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samplingStateToHeader @Text tcSamplingState <&> \t ->
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"sampling_state" .= t
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in J.object $ idFields ++ maybeToList samplingFieldMaybe
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