[AIRFLOW-2861] Add index on log table (apache#3709)

Author: vardancse

airflow/migrations/versions/dd25f486b8ea_add_idx_log_dag.py

@@ -0,0 +1,41 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+from alembic import op
+
+"""add idx_log_dag
+
+Revision ID: dd25f486b8ea
+Revises: 9635ae0956e7
+Create Date: 2018-08-07 06:41:41.028249
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'dd25f486b8ea'
+down_revision = '9635ae0956e7'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_index('idx_log_dag', 'log', ['dag_id'], unique=False)
+
+
+def downgrade():
+    op.drop_index('idx_log_dag', table_name='log')

airflow/models.py

@@ -2110,6 +2110,10 @@ class Log(Base):
     owner = Column(String(500))
     extra = Column(Text)
 
+    __table_args__ = (
+        Index('idx_log_dag', dag_id),
+    )
+
     def __init__(self, event, task_instance, owner=None, extra=None, **kwargs):
         self.dttm = timezone.utcnow()
         self.event = event