[GitHub] [airflow] uranusjr commented on a change in pull request #20975: Switch XCom implementation to use run_id

[GitBox <gi...@apache.org>]

uranusjr commented on a change in pull request #20975:
URL: https://github.com/apache/airflow/pull/20975#discussion_r798674672



##########
File path: airflow/migrations/versions/c306b5b5ae4a_switch_xcom_table_to_use_run_id.py
##########
@@ -0,0 +1,139 @@
+#
+# 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.
+
+"""Switch XCom table to use ``run_id``.
+
+Revision ID: c306b5b5ae4a
+Revises: e655c0453f75
+Create Date: 2022-01-19 03:20:35.329037
+"""
+from typing import Sequence
+
+from alembic import op
+from sqlalchemy import Column, Index, Integer, LargeBinary, MetaData, Table, select
+
+from airflow.migrations.db_types import TIMESTAMP, StringID
+
+# Revision identifiers, used by Alembic.
+revision = "c306b5b5ae4a"
+down_revision = "e655c0453f75"
+branch_labels = None
+depends_on = None
+
+
+metadata = MetaData()
+
+dagrun = Table(
+    "dag_run",
+    metadata,
+    Column("id", Integer, primary_key=True),
+    Column("dag_id", StringID(), nullable=False),
+    Column("run_id", StringID(), nullable=False),
+    Column("execution_date", TIMESTAMP, nullable=False),
+)
+
+
+def _get_new_xcom_columns() -> Sequence[Column]:
+    return [
+        Column("dagrun_id", Integer(), nullable=False, primary_key=True),
+        Column("task_id", StringID(), nullable=False, primary_key=True),
+        Column("key", StringID(length=512), nullable=False, primary_key=True),
+        Column("value", LargeBinary),
+        Column("timestamp", TIMESTAMP, nullable=False),
+        Column("dag_id", StringID(), nullable=False),
+        Column("run_id", StringID(), nullable=False),
+    ]
+
+
+def _get_old_xcom_columns() -> Sequence[Column]:
+    return [
+        Column("key", StringID(length=512), nullable=False, primary_key=True),
+        Column("value", LargeBinary),
+        Column("timestamp", TIMESTAMP, nullable=False, primary_key=True),
+        Column("task_id", StringID(), nullable=False, primary_key=True),
+        Column("dag_id", StringID(), nullable=False, primary_key=True),
+        Column("execution_date", StringID(), nullable=False, primary_key=True),
+    ]
+
+
+def upgrade():
+    """Switch XCom table to use run_id.
+
+    For performance reasons, this is done by creating a new table with needed
+    data pre-populated, adding back constraints we need, and renaming it to
+    replace the existing XCom table.
+    """
+    op.create_table(
+        "__airflow_tmp_xcom",
+        *_get_new_xcom_columns(),
+        Index("idx_xcom_key", "key"),

Review comment:
       Ah right, that’s my original intention behind the create-table-copy-rename strategy, but it somehow got lost after so many iterations.




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