From 8ea24b289045ee841136cb29fd599c75241d8de6 Mon Sep 17 00:00:00 2001
From: steve-chavez <stevechavezast@gmail.com>
Date: Fri, 19 Apr 2024 23:00:15 -0500
Subject: [PATCH] feat: schema cache metrics

---
 src/PostgREST/Metrics.hs | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/PostgREST/Metrics.hs b/src/PostgREST/Metrics.hs
index cbf56e03b23..d22dcf0e504 100644
--- a/src/PostgREST/Metrics.hs
+++ b/src/PostgREST/Metrics.hs
@@ -1,5 +1,4 @@
-{-# LANGUAGE NamedFieldPuns #-}
-{-# LANGUAGE NumericUnderscores #-}
+{-# LANGUAGE NamedFieldPuns     #-}
 module PostgREST.Metrics
   ( init
   , MetricsState (..)
@@ -21,6 +20,8 @@ data MetricsState = MetricsState
   , poolAvailable        :: Prom.Gauge
   , poolWaiting          :: Prom.Gauge
   , poolMaxSize          :: Prom.Gauge
+  , schemaCacheLoads     :: Prom.Counter
+  , schemaCacheQueryTime :: Prom.Gauge
   }
 
 init :: Int -> IO MetricsState
@@ -29,11 +30,13 @@ init poolMaxSize = do
   available <- Prom.register $ Prom.gauge (Prom.Info "pgrst_db_pool_available" "Available connections in the pool")
   waiting <- Prom.register $ Prom.gauge (Prom.Info "pgrst_db_pool_waiting" "Requests waiting to acquire a pool connection")
   maxSize <- Prom.register $ Prom.gauge (Prom.Info "pgrst_db_pool_max" "Max pool connections")
+  sCacheLoads <- Prom.register $ Prom.counter (Prom.Info "pgrst_schema_cache_loads_total" "The total number of times the schema cache was loaded")
+  sCacheQTime <- Prom.register $ Prom.gauge (Prom.Info "pgrst_schema_cache_query_time_seconds" "The query time in seconds of the last schema cache load")
   Prom.setGauge maxSize (fromIntegral poolMaxSize)
-  pure $ MetricsState timeouts available waiting maxSize
+  pure $ MetricsState timeouts available waiting maxSize sCacheLoads sCacheQTime
 
 observationMetrics :: MetricsState -> ObservationHandler
-observationMetrics MetricsState{poolTimeouts, poolAvailable, poolWaiting} obs = case obs of
+observationMetrics MetricsState{poolTimeouts, poolAvailable, poolWaiting, schemaCacheLoads, schemaCacheQueryTime} obs = case obs of
   (PoolAcqTimeoutObs _) -> do
     Prom.incCounter poolTimeouts
   (HasqlPoolObs (SQL.ConnectionObservation _ status)) -> case status of
@@ -48,6 +51,9 @@ observationMetrics MetricsState{poolTimeouts, poolAvailable, poolWaiting} obs =
     Prom.incGauge poolWaiting
   PoolRequestFullfilled ->
     Prom.decGauge poolWaiting
+  SchemaCacheLoadedObs resTime -> do
+    Prom.incCounter schemaCacheLoads
+    Prom.setGauge schemaCacheQueryTime resTime
   _ ->
     pure ()