feat: Log PoolRequest and PoolRequestFullfilled observations (#3925)

src/PostgREST/Logger.hs

@@ -94,10 +94,12 @@ observationLogger loggerState logLevel obs = case obs of
     -- Does not log SQL when it's empty (for OPTIONS requests or for the default OpenAPI output)
     when (sql /= mempty && shouldLogResponse logLevel status) $ do
       logWithZTime loggerState $ observationMessage o
-  PoolRequest ->
-    pure ()
-  PoolRequestFullfilled ->
-    pure ()
+  o@PoolRequest ->
+    when (logLevel >= LogDebug) $ do
+      logWithZTime loggerState $ observationMessage o
+  o@PoolRequestFullfilled ->
+    when (logLevel >= LogDebug) $ do
+      logWithZTime loggerState $ observationMessage o
   o ->
     logWithZTime loggerState $ observationMessage o
 

src/PostgREST/Observation.hs

@@ -142,7 +142,10 @@ observationMessage = \case
           SQL.ReleaseConnectionTerminationReason        -> "release"
           SQL.NetworkErrorConnectionTerminationReason _ -> "network error" -- usage error is already logged, no need to repeat the same message.
     )
-  _ -> mempty
+  PoolRequest ->
+    "Trying to borrow a connection from pool"
+  PoolRequestFullfilled ->
+    "Borrowed a connection from the pool"
   where
     showMillis :: Double -> Text
     showMillis x = toS $ showFFloat (Just 1) (x * 1000) ""