fix(users/Profpatsch/MonadPostgres): take old formatter process r/8138

The pool library would always take out the most recently used perl
resource again, and since that is the one that we just spawned, we’d
be back at square one. Instead, we try to find an older one (or up to
200ms old) and use that instead, because that should be the one with
the fastest response time.

Okay, that was enough bullshit lol.

Change-Id: I6b999e682d02ab03206a9d1b707edf16daa04a0d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11657
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>
Autosubmit: Profpatsch <mail@profpatsch.de>

1 files changed, 29 insertions, 4 deletions

diff --git a/users/Profpatsch/my-prelude/src/Postgres/MonadPostgres.hs b/users/Profpatsch/my-prelude/src/Postgres/MonadPostgres.hs
index 57daeb3ace..a542f8c7b8 100644
--- a/users/Profpatsch/my-prelude/src/Postgres/MonadPostgres.hs
+++ b/users/Profpatsch/my-prelude/src/Postgres/MonadPostgres.hs
@@ -5,6 +5,7 @@
 
 module Postgres.MonadPostgres where
 
+import Arg
 import AtLeast (AtLeast)
 import Control.Exception
   ( Exception (displayException),
@@ -26,7 +27,6 @@ import Data.List qualified as List
 import Data.Pool (Pool)
 import Data.Pool qualified as Pool
 import Data.Text qualified as Text
-import Data.Time (getCurrentTime)
 import Data.Typeable (Typeable)
 import Database.PostgreSQL.Simple (Connection, FormatError, FromRow, Query, QueryError, ResultError, SqlError, ToRow)
 import Database.PostgreSQL.Simple qualified as PG
@@ -48,7 +48,7 @@ import Pretty (showPretty)
 import Seconds
 import System.Exit (ExitCode (..))
 import Tool
-import UnliftIO (MonadUnliftIO (withRunInIO), bracket, hClose)
+import UnliftIO (MonadUnliftIO (withRunInIO), bracket, hClose, mask_)
 import UnliftIO.Concurrent (forkIO)
 import UnliftIO.Process (ProcessHandle)
 import UnliftIO.Process qualified as Process
@@ -429,7 +429,8 @@ data PgFormatProcess = PgFormatProcess
   { stdinHdl :: Handle,
     stdoutHdl :: Handle,
     stderrHdl :: Handle,
-    procHdl :: ProcessHandle
+    procHdl :: ProcessHandle,
+    startedAt :: Otel.Timestamp
   }
 
 initPgFormatPool :: (HasField "pgFormat" tools Tool) => tools -> IO PgFormatPool
@@ -463,11 +464,34 @@ initPgFormatPool tools = do
 destroyPgFormatPool :: PgFormatPool -> IO ()
 destroyPgFormatPool pool = Pool.destroyAllResources pool.pool
 
+-- | Get the oldest resource from the pool, or stop if you find a resource that’s older than `cutoffPointMs`.
+takeOldestResource :: PgFormatPool -> Arg "cutoffPointMs" Integer -> IO (PgFormatProcess, Pool.LocalPool PgFormatProcess)
+takeOldestResource pool cutoffPointMs = do
+  now <- Otel.getTimestamp
+  mask_ $ do
+    a <- Pool.takeResource pool.pool
+    (putBack, res) <- go now [] a
+    -- make sure we don’t leak any resources we didn’t use in the end
+    for_ putBack $ \(x, xLocal) -> Pool.putResource xLocal x
+    pure res
+  where
+    mkMs ts = (ts & Otel.timestampNanoseconds & toInteger) `div` 1000_000
+    go now putBack a@(a', _) =
+      if abs (mkMs now - mkMs a'.startedAt) > cutoffPointMs.unArg
+        then pure (putBack, a)
+        else
+          Pool.tryTakeResource pool.pool >>= \case
+            Nothing -> pure (putBack, a)
+            Just b@(b', _) -> do
+              if a'.startedAt < b'.startedAt
+                then go now (b : putBack) a
+                else go now (a : putBack) b
+
 -- | Format the given SQL with pg_formatter. Will use the pool of already running formatters to speed up execution.
 runPgFormat :: PgFormatPool -> ByteString -> IO (T3 "exitCode" ExitCode "formatted" ByteString "stderr" ByteString)
 runPgFormat pool sqlStatement = do
   bracket
-    (Pool.takeResource pool.pool)
+    (takeOldestResource pool 200)
     ( \(a, localPool) -> do
         -- we always destroy the resource, because the process exited
         Pool.destroyResource pool.pool localPool a
@@ -772,6 +796,7 @@ pgFormatStartCommandWaitForInput ::
   m PgFormatProcess
 pgFormatStartCommandWaitForInput tools = do
   do
+    startedAt <- Otel.getTimestamp
     (Just stdinHdl, Just stdoutHdl, Just stderrHdl, procHdl) <-
       Process.createProcess
         ( ( Process.proc