Close connections to db, and print any exceptions encountered

Were were running out of db connections, but not seeing the exception
message, because it's only raised in the original process if we ask for
the result.

iatidata/__init__.py

@@ -11,6 +11,7 @@
 import subprocess
 import tempfile
 import time
+import traceback
 import zipfile
 from collections import defaultdict
 from datetime import datetime
@@ -305,7 +306,9 @@ def load_dataset(dataset: iatikit.Dataset) -> None:
     path = pathlib.Path(dataset.data_path)
     prefix, filename = path.parts[-2:]
 
-    with get_engine().begin() as connection:
+    engine = get_engine()
+
+    with engine.begin() as connection:
         connection.execute(
             insert(
                 table(
@@ -334,6 +337,8 @@ def load_dataset(dataset: iatikit.Dataset) -> None:
             )
         )
 
+    engine.dispose()
+
 
 def create_database_schema():
     if schema:
@@ -363,6 +368,12 @@ def load(processes: int, sample: Optional[int] = None) -> None:
             executor.submit(load_dataset, dataset) for dataset in datasets_sample
         ]
         concurrent.futures.wait(futures)
+        # We have to get the result (even though we don't use it) in order to get the exceptions
+         for future in futures:
+            try:
+                future.result()
+            except Exception:
+                print(traceback.format_exc())
 
     engine = get_engine()
     with engine.begin() as connection: