Fixed #19861 -- Transaction ._dirty flag improvement

There were a couple of errors in ._dirty flag handling:
  * It started as None, but was never reset to None.
  * The _dirty flag was sometimes used to indicate if the connection
    was inside transaction management, but this was not done
    consistently. This also meant the flag had three separate values.
  * The None value had a special meaning, causing for example inability
    to commit() on new connection unless enter/leave tx management was
    done.
  * The _dirty was tracking "connection in transaction" state, but only
    in managed transactions.
  * Some tests never reset the transaction state of the used connection.
  * And some additional less important changes.

This commit has some potential for regressions, but as the above list
shows, the current situation isn't perfect either.

1 files changed, 0 insertions, 5 deletions

diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index 22d025ecb2..b9d25d98a1 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -687,11 +687,6 @@ class SQLCompiler(object):
         resolve_columns = hasattr(self, 'resolve_columns')
         fields = None
         has_aggregate_select = bool(self.query.aggregate_select)
-        # Set transaction dirty if we're using SELECT FOR UPDATE to ensure
-        # a subsequent commit/rollback is executed, so any database locks
-        # are released.
-        if self.query.select_for_update and transaction.is_managed(self.using):
-            transaction.set_dirty(self.using)
         for rows in self.execute_sql(MULTI):
             for row in rows:
                 if resolve_columns: