[EWT-450] fixing sla miss triggering duplicate alerts every minute (a…

…pache#56)

Co-authored-by: Vishesh Jain <visheshj@twitter.com>

airflow/migrations/versions/a982338e6d7f_sla_miss_execution_time_on_update_.py

@@ -0,0 +1,77 @@
+#
+# 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.
+
+"""sla miss execution_time on update current time fix
+
+Revision ID: a982338e6d7f
+Revises: 0e2a74e0fc9f
+Create Date: 2020-09-01 13:48:03.093594
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'a982338e6d7f'
+down_revision = '0e2a74e0fc9f'
+branch_labels = None
+depends_on = None
+
+from alembic import op
+from sqlalchemy.dialects import mysql
+from sqlalchemy import text
+
+
+def upgrade():
+    conn = op.get_bind()
+    if conn.dialect.name == "mysql":
+        # NOTE:
+        #
+        # This patch is internal to Twitter, Here we explicitly set a default to the string literal
+        # `CURRENT_TIMESTAMP(6)` to avoid the
+        # default MySQL behavior for TIMESTAMP without `explicit_defaults_for_timestamp` turned
+        # on as stated here:
+        #
+        #  "The first TIMESTAMP column in a table, if not explicitly declared with the NULL
+        #  attribute or an explicit
+        #   DEFAULT or ON UPDATE attribute, is automatically declared with the DEFAULT
+        #   CURRENT_TIMESTAMP and
+        #   ON UPDATE CURRENT_TIMESTAMP attributes." [0]
+        #
+        # Because of the "ON UPDATE CURRENT_TIMESTAMP" default, anytime the `sla_miss` table
+        # is UPDATE'd without
+        # explicitly re-passing the current value for the `execution_date` column, it will end up
+        # getting clobbered with
+        # the current timestamp value which breaks sla functionality and
+        # causes duplicate alerts every minute.
+        #
+        # We unfortunately cannot turn `explicit_defaults_for_timestamp` on globally ourselves as
+        # is now technically
+        # required by Airflow [1], because this has to be set in the my.cnf and we don't control
+        # that in managed MySQL.
+        # A request to enable this fleet-wide has been made in MVP-18609.
+        #
+        # [0]: https://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html
+        # #sysvar_explicit_defaults_for_timestamp
+        # [1]: https://github.com/apache/incubator-airflow/blob/master/UPDATING.md#mysql-setting
+        # -required
+        op.alter_column(table_name='sla_miss', column_name='execution_date',
+            type_=mysql.TIMESTAMP(fsp=6), nullable=False,
+            server_default=text('CURRENT_TIMESTAMP(6)'))
+
+
+def downgrade():
+    pass

airflow/version.py

@@ -18,5 +18,5 @@
 # under the License.
 #
 
-version = '1.10.4+twtr15'
+version = '1.10.4+twtr16'