Delete old email_log entries in batches to avoid table lock (#1902)

* Delete old email_log entries in batches to avoid table lock

* Avoid nested join

* Commiting after the batch delete

* Added statement count print

* Rename var

cron.py

@@ -9,7 +9,7 @@ from sqlalchemy import func, desc, or_, and_
 from sqlalchemy.ext.compiler import compiles
 from sqlalchemy.orm import joinedload
 from sqlalchemy.orm.exc import ObjectDeletedError
-from sqlalchemy.sql import Insert
+from sqlalchemy.sql import Insert, text
 
 from app import s3, config
 from app.alias_utils import nb_email_log_for_mailbox
@@ -85,23 +85,43 @@ def delete_logs():
     delete_refused_emails()
     delete_old_monitoring()
 
-    for t in TransactionalEmail.filter(
+    for t_email in TransactionalEmail.filter(
         TransactionalEmail.created_at < arrow.now().shift(days=-7)
     ):
-        TransactionalEmail.delete(t.id)
+        TransactionalEmail.delete(t_email.id)
 
     for b in Bounce.filter(Bounce.created_at < arrow.now().shift(days=-7)):
         Bounce.delete(b.id)
 
     Session.commit()
 
-    LOG.d("Delete EmailLog older than 2 weeks")
+    LOG.d("Deleting EmailLog older than 2 weeks")
 
-    max_dt = arrow.now().shift(weeks=-2)
-    nb_deleted = EmailLog.filter(EmailLog.created_at < max_dt).delete()
-    Session.commit()
+    total_deleted = 0
+    batch_size = 500
+    Session.execute("set session statement_timeout=30000").rowcount
+    queries_done = 0
+    cutoff_time = arrow.now().shift(days=-14)
+    rows_to_delete = EmailLog.filter(EmailLog.created_at < cutoff_time).count()
+    expected_queries = int(rows_to_delete / batch_size)
+    sql = text(
+        f"DELETE FROM email_log WHERE id IN (SELECT id FROM email_log WHERE created_at < :cutoff_time order by created_at limit :batch_size)"
+    )
+    str_cutoff_time = cutoff_time.isoformat()
+    while total_deleted < rows_to_delete:
+        deleted_count = Session.execute(
+            sql, {"cutoff_time": str_cutoff_time, "batch_size": batch_size}
+        ).rowcount
+        Session.commit()
+        total_deleted += deleted_count
+        queries_done += 1
+        LOG.i(
+            f"[{queries_done}/{expected_queries}] Deleted {total_deleted} EmailLog entries"
+        )
+        if deleted_count < batch_size:
+            break
 
-    LOG.i("Delete %s email logs", nb_deleted)
+    LOG.i("Deleted %s email logs", total_deleted)
 
 
 def delete_refused_emails():