graphql-engine/server/src-lib/Hasura/Backends/MySQL/Instances/Transport.hs
Antoine Leblanc cf531b05cb Rewrite Tracing to allow for only one TraceT in the entire stack.
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
2023-03-13 17:38:39 +00:00

81 lines
2.5 KiB
Haskell

{-# OPTIONS_GHC -fno-warn-orphans #-}
module Hasura.Backends.MySQL.Instances.Transport (runQuery) where
import Control.Monad.Trans.Control
import Data.Aeson qualified as J
import Data.Text.Extended
import Hasura.Backends.MySQL.Instances.Execute ()
import Hasura.Base.Error
import Hasura.EncJSON
import Hasura.GraphQL.Execute.Backend
import Hasura.GraphQL.Logging
import Hasura.GraphQL.Namespace (RootFieldAlias)
import Hasura.GraphQL.Transport.Backend
import Hasura.GraphQL.Transport.HTTP.Protocol
import Hasura.Logging qualified as L
import Hasura.Prelude
import Hasura.RQL.Types.Backend
import Hasura.SQL.Backend
import Hasura.Server.Types (RequestId)
import Hasura.Session
import Hasura.Tracing
instance BackendTransport 'MySQL where
runDBQuery = runQuery
runDBQueryExplain = runQueryExplain
runDBMutation = error "runDBMutation: MySQL backend does not support this operation yet."
runDBSubscription = error "runDBSubscription: MySQL backend does not support this operation yet."
runDBStreamingSubscription = error "runDBStreamingSubscription: MySQL backend does not support this operation yet"
runQuery ::
( MonadIO m,
MonadBaseControl IO m,
MonadQueryLog m,
MonadTrace m,
MonadError QErr m
) =>
RequestId ->
GQLReqUnparsed ->
RootFieldAlias ->
UserInfo ->
L.Logger L.Hasura ->
SourceConfig 'MySQL ->
OnBaseMonad IdentityT EncJSON ->
Maybe (PreparedQuery 'MySQL) ->
ResolvedConnectionTemplate 'MySQL ->
-- | Also return the time spent in the PG query; for telemetry.
m (DiffTime, EncJSON)
runQuery reqId query fieldName _userInfo logger _sourceConfig tx genSql _ = do
logQueryLog logger $ mkQueryLog query fieldName genSql reqId
withElapsedTime $
newSpan ("MySQL Query for root field " <>> fieldName) $
run tx
runQueryExplain ::
( MonadIO m,
MonadBaseControl IO m,
MonadError QErr m,
MonadTrace m
) =>
DBStepInfo 'MySQL ->
m EncJSON
runQueryExplain (DBStepInfo _ _ _ action _) = run action
run :: (MonadIO m, MonadBaseControl IO m, MonadError QErr m, MonadTrace m) => OnBaseMonad IdentityT a -> m a
run = runIdentityT . runOnBaseMonad
mkQueryLog ::
GQLReqUnparsed ->
RootFieldAlias ->
Maybe (PreparedQuery 'MySQL) ->
RequestId ->
QueryLog
mkQueryLog gqlQuery fieldName preparedSql requestId =
-- @QueryLogKindDatabase Nothing@ means that the backend doesn't support connection templates
QueryLog gqlQuery ((fieldName,) <$> generatedQuery) requestId (QueryLogKindDatabase Nothing)
where
generatedQuery =
preparedSql <&> \queryString ->
GeneratedQuery queryString J.Null