ephraimbuddy commented on a change in pull request #21462:
URL: https://github.com/apache/airflow/pull/21462#discussion_r803157245
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File path: airflow/models/taskinstance.py
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@@ -386,6 +385,7 @@ class TaskInstance(Base, LoggingMixin):
Index('ti_pool', pool, state, priority_weight),
Index('ti_job_id', job_id),
Index('ti_trigger_id', trigger_id),
+ Index('ti_map_index', dag_id, task_id, run_id, map_index, unique=True),
Review comment:
Both MySQL and MSSQL required this. Here is the error from MySQL:
```sql
sqlalchemy.exc.OperationalError: (MySQLdb._exceptions.OperationalError)
(1822, "Failed to add the foreign key constraint. Missing index for constraint
'task_map_task_instance_fkey' in the referenced table 'task_instance'")
[SQL:
CREATE TABLE task_map (
dag_id VARCHAR(250) COLLATE utf8mb3_bin NOT NULL,
task_id VARCHAR(250) COLLATE utf8mb3_bin NOT NULL,
run_id VARCHAR(250) COLLATE utf8mb3_bin NOT NULL,
map_index INTEGER NOT NULL,
length INTEGER NOT NULL,
`keys` JSON,
PRIMARY KEY (dag_id, task_id, run_id, map_index),
CONSTRAINT task_map_length_not_negative CHECK (length >= 0),
CONSTRAINT task_map_task_instance_fkey FOREIGN KEY(dag_id, task_id,
run_id, map_index) REFERENCES task_instance (dag_id, task_id, run_id,
map_index) ON DELETE CASCADE
)
```
The unique=True was required by MSSQL:
```sql
sqlalchemy.exc.ProgrammingError: (pyodbc.ProgrammingError) ('42000',
"[42000] [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]There are no
primary or candidate keys in the referenced table 'task_instance' that match
the referencing column list in the foreign key 'task_map_task_instance_fkey'.
(1776) (SQLExecDirectW)")
[SQL:
CREATE TABLE task_map (
dag_id VARCHAR(250) NOT NULL,
task_id VARCHAR(250) NOT NULL,
run_id VARCHAR(250) NOT NULL,
map_index INTEGER NOT NULL,
length INTEGER NOT NULL,
keys NVARCHAR(max) NULL,
PRIMARY KEY (dag_id, task_id, run_id, map_index),
CONSTRAINT task_map_length_not_negative CHECK (length >= 0),
CONSTRAINT task_map_task_instance_fkey FOREIGN KEY(dag_id, task_id,
run_id, map_index) REFERENCES task_instance (dag_id, task_id, run_id,
map_index) ON DELETE CASCADE
)
```
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