Use RepeatableRead isolation level

Author: lazamar

src/Ambar/Emulator/Connector/Postgres.hs

@@ -186,7 +186,7 @@ connect config@PostgreSQL{..} logger (PostgreSQLState tracker) producer f =
        P.withTransactionMode txMode conn $ foldM pollSection acc0 (splitBoundaries bounds)
        where
        txMode = P.TransactionMode
-          { P.isolationLevel = P.ReadCommitted
+          { P.isolationLevel = P.RepeatableRead
           , P.readWriteMode = P.ReadOnly
           }
 

tests/Test/Connector/PostgreSQL.hs

@@ -57,16 +57,20 @@ testPostgreSQL p = do
 
     it "handles large boundary lists" $ do
       with (PartitionCount 1) $ \conn table topic connected -> do
-        void $ P.execute_ conn
-          (fromString $ "ALTER SEQUENCE " <> tableName table <> "_id_seq INCREMENT BY 2")
-        let n = 10000
-        insert conn table (take n $ head $ mocks table)
-        connected $
-          deadline (seconds 10) $
-          Topic.withConsumer topic group $ \consumer -> do
-            forM_ [1..n] $ \_ -> void $ readEntry @Event consumer
-            insert conn table [head (mocks table !! 1)]
-            void $ readEntry @Event consumer
+        void $ P.execute_ conn $ fromString $
+          "ALTER SEQUENCE " <> tableName table <> "_id_seq INCREMENT BY 2"
+
+        let n = 50000
+        connected $ Topic.withConsumer topic group $ \consumer -> deadline (seconds 10) $ do
+          -- pre-fill the table
+          insert conn table (take n $ head $ mocks table)
+          -- advance connector.
+          forM_ [1..n] $ \_ -> readEntry @Event consumer
+
+          -- now insert and expect a new entry, which will definitely be retrieved from a query
+          -- containing lots of gaps.
+          insert conn table [head (mocks table !! 1)]
+          void $ readEntry @Event consumer
 
     -- Test that column types are supported/unsupported by
     -- creating database entries with the value and reporting