[CP][EWT-302]Patch Pool.DEFAULT_POOL_NAME in BaseOperator (apache#8587) (#49)

Open source commit id: b37ce29

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

Author: vshshjn7

UPDATING.md

@@ -22,6 +22,18 @@ under the License.
 This file documents any backwards-incompatible changes in Airflow and
 assists users migrating to a new version.
 
+## CP
+
+### Ability to patch Pool.DEFAULT_POOL_NAME in BaseOperator
+It was not possible to patch pool in BaseOperator as the signature sets the default value of pool
+as Pool.DEFAULT_POOL_NAME.
+While using subdagoperator in unittest(without initializing the sqlite db), it was throwing the
+following error:
+```
+sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such table: slot_pool.
+```
+Fix for this, https://github.com/apache/airflow/pull/8587
+
 ## Airflow 1.10.4
 
 ### Python 2 support is going away
@@ -36,12 +48,12 @@ If you have a specific task that still requires Python 2 then you can use the Py
 
 ### Changes to GoogleCloudStorageHook
 
-* the discovery-based api (`googleapiclient.discovery`) used in `GoogleCloudStorageHook` is now replaced by the recommended client based api (`google-cloud-storage`). To know the difference between both the libraries, read https://cloud.google.com/apis/docs/client-libraries-explained. PR: [#5054](https://github.com/apache/airflow/pull/5054) 
+* the discovery-based api (`googleapiclient.discovery`) used in `GoogleCloudStorageHook` is now replaced by the recommended client based api (`google-cloud-storage`). To know the difference between both the libraries, read https://cloud.google.com/apis/docs/client-libraries-explained. PR: [#5054](https://github.com/apache/airflow/pull/5054)
 * as a part of this replacement, the `multipart` & `num_retries` parameters for `GoogleCloudStorageHook.upload` method have been deprecated.
-  
+
   The client library uses multipart upload automatically if the object/blob size is more than 8 MB - [source code](https://github.com/googleapis/google-cloud-python/blob/11c543ce7dd1d804688163bc7895cf592feb445f/storage/google/cloud/storage/blob.py#L989-L997). The client also handles retries automatically
 
-* the `generation` parameter is deprecated in `GoogleCloudStorageHook.delete` and `GoogleCloudStorageHook.insert_object_acl`. 
+* the `generation` parameter is deprecated in `GoogleCloudStorageHook.delete` and `GoogleCloudStorageHook.insert_object_acl`.
 
 Updating to `google-cloud-storage >= 1.16` changes the signature of the upstream `client.get_bucket()` method from `get_bucket(bucket_name: str)` to `get_bucket(bucket_or_name: Union[str, Bucket])`. This method is not directly exposed by the airflow hook, but any code accessing the connection directly (`GoogleCloudStorageHook().get_conn().get_bucket(...)` or similar) will need to be updated.
 
@@ -305,7 +317,7 @@ then you need to change it like this
     @property
     def is_active(self):
       return self.active
-      
+
 ### Support autodetected schemas to GoogleCloudStorageToBigQueryOperator
 
 GoogleCloudStorageToBigQueryOperator is now support schema auto-detection is available when you load data into BigQuery. Unfortunately, changes can be required.
@@ -317,7 +329,7 @@ define a schema_fields:
     gcs_to_bq.GoogleCloudStorageToBigQueryOperator(
       ...
       schema_fields={...})
-      
+
 or define a schema_object:
 
     gcs_to_bq.GoogleCloudStorageToBigQueryOperator(

airflow/models/baseoperator.py

@@ -281,7 +281,7 @@ def __init__(
         priority_weight=1,  # type: int
         weight_rule=WeightRule.DOWNSTREAM,  # type: str
         queue=configuration.conf.get('celery', 'default_queue'),  # type: str
-        pool=Pool.DEFAULT_POOL_NAME,  # type: str
+        pool=None,  # type: str
         sla=None,  # type: Optional[timedelta]
         execution_timeout=None,  # type: Optional[timedelta]
         on_failure_callback=None,  # type: Optional[Callable]
@@ -351,7 +351,7 @@ def __init__(
         self.retries = retries if retries is not None else \
             int(configuration.conf.get('core', 'default_task_retries', fallback=0))
         self.queue = queue
-        self.pool = pool
+        self.pool = Pool.DEFAULT_POOL_NAME if pool is None else pool
         self.sla = sla
         self.execution_timeout = execution_timeout
         self.on_failure_callback = on_failure_callback