graphql-engine/server/src-lib/Hasura/Server/Prometheus.hs

-- | Mutable references for Prometheus metrics.
--
-- These metrics are independent from the metrics in "Hasura.Server.Metrics".
module Hasura.Server.Prometheus
  ( PrometheusMetrics (..),
    GraphQLRequestMetrics (..),
    EventTriggerMetrics (..),
    makeDummyPrometheusMetrics,
    ConnectionsGauge,
    Connections (..),
    newConnectionsGauge,
    readConnectionsGauge,
    incWarpThreads,
    decWarpThreads,
    incWebsocketConnections,
    decWebsocketConnections,
  )
where

import Data.IORef (IORef, atomicModifyIORef', newIORef, readIORef)
import Data.Int (Int64)
import Hasura.Prelude
import System.Metrics.Prometheus.Counter (Counter)
import System.Metrics.Prometheus.Counter qualified as Counter
import System.Metrics.Prometheus.Gauge (Gauge)
import System.Metrics.Prometheus.Gauge qualified as Gauge
import System.Metrics.Prometheus.Histogram (Histogram)
import System.Metrics.Prometheus.Histogram qualified as Histogram

--------------------------------------------------------------------------------

-- | Mutable references for Prometheus metrics.
data PrometheusMetrics = PrometheusMetrics
  { pmConnections :: ConnectionsGauge,
    pmActiveSubscriptions :: Gauge,
    pmGraphQLRequestMetrics :: GraphQLRequestMetrics,
    pmEventTriggerMetrics :: EventTriggerMetrics
  }

data GraphQLRequestMetrics = GraphQLRequestMetrics
  { gqlRequestsQuerySuccess :: Counter,
    gqlRequestsQueryFailure :: Counter,
    gqlRequestsMutationSuccess :: Counter,
    gqlRequestsMutationFailure :: Counter,
    gqlRequestsUnknownFailure :: Counter,
    gqlExecutionTimeSecondsQuery :: Histogram,
    gqlExecutionTimeSecondsMutation :: Histogram
  }

data EventTriggerMetrics = EventTriggerMetrics
  { eventTriggerHTTPWorkers :: Gauge,
    eventQueueTimeSeconds :: Histogram
  }

-- | Create dummy mutable references without associating them to a metrics
-- store.
makeDummyPrometheusMetrics :: IO PrometheusMetrics
makeDummyPrometheusMetrics = do
  pmConnections <- newConnectionsGauge
  pmActiveSubscriptions <- Gauge.new
  pmGraphQLRequestMetrics <- makeDummyGraphQLRequestMetrics
  pmEventTriggerMetrics <- makeDummyEventTriggerMetrics
  pure PrometheusMetrics {..}

makeDummyGraphQLRequestMetrics :: IO GraphQLRequestMetrics
makeDummyGraphQLRequestMetrics = do
  gqlRequestsQuerySuccess <- Counter.new
  gqlRequestsQueryFailure <- Counter.new
  gqlRequestsMutationSuccess <- Counter.new
  gqlRequestsMutationFailure <- Counter.new
  gqlRequestsUnknownFailure <- Counter.new
  gqlExecutionTimeSecondsQuery <- Histogram.new []
  gqlExecutionTimeSecondsMutation <- Histogram.new []
  pure GraphQLRequestMetrics {..}

makeDummyEventTriggerMetrics :: IO EventTriggerMetrics
makeDummyEventTriggerMetrics = do
  eventTriggerHTTPWorkers <- Gauge.new
  eventQueueTimeSeconds <- Histogram.new []
  pure EventTriggerMetrics {..}

--------------------------------------------------------------------------------

-- | A mutable reference for atomically sampling the number of websocket
-- connections and number of threads forked by the warp webserver.
--
-- Because we derive the number of (non-websocket) HTTP connections by the
-- difference of these two metrics, we must sample them simultaneously,
-- otherwise we might report a negative number of HTTP connections.
newtype ConnectionsGauge = ConnectionsGauge (IORef Connections)

data Connections = Connections
  { connWarpThreads :: Int64,
    connWebsockets :: Int64
  }

newConnectionsGauge :: IO ConnectionsGauge
newConnectionsGauge =
  ConnectionsGauge
    <$> newIORef Connections {connWarpThreads = 0, connWebsockets = 0}

readConnectionsGauge :: ConnectionsGauge -> IO Connections
readConnectionsGauge (ConnectionsGauge ref) = readIORef ref

incWarpThreads :: ConnectionsGauge -> IO ()
incWarpThreads =
  modifyConnectionsGauge $ \connections ->
    connections {connWarpThreads = connWarpThreads connections + 1}

decWarpThreads :: ConnectionsGauge -> IO ()
decWarpThreads =
  modifyConnectionsGauge $ \connections ->
    connections {connWarpThreads = connWarpThreads connections - 1}

incWebsocketConnections :: ConnectionsGauge -> IO ()
incWebsocketConnections =
  modifyConnectionsGauge $ \connections ->
    connections {connWebsockets = connWebsockets connections + 1}

decWebsocketConnections :: ConnectionsGauge -> IO ()
decWebsocketConnections =
  modifyConnectionsGauge $ \connections ->
    connections {connWebsockets = connWebsockets connections - 1}

modifyConnectionsGauge ::
  (Connections -> Connections) -> ConnectionsGauge -> IO ()
modifyConnectionsGauge f (ConnectionsGauge ref) =
  atomicModifyIORef' ref $ \connections -> (f connections, ())