[cherry-pick] migrate all dashboards

.pylintrc

@@ -282,7 +282,7 @@ ignored-modules=numpy,pandas,alembic.op,sqlalchemy,alembic.context,flask_appbuil
 # List of class names for which member attributes should not be checked (useful
 # for classes with dynamically set attributes). This supports the use of
 # qualified names.
-ignored-classes=optparse.Values,thread._local,_thread._local,sqlalchemy.orm.scoping.scoped_session
+ignored-classes=contextlib.closing,optparse.Values,thread._local,_thread._local,sqlalchemy.orm.scoping.scoped_session
 
 # List of members which are set dynamically and missed by pylint inference
 # system, and so shouldn't trigger E1101 when accessed. Python regular

CONTRIBUTING.md

@@ -505,3 +505,21 @@ https://github.com/apache/incubator-superset/pull/3013
   with a PGP key and providing MD5, Apache voting, as well as
   publishing to Apache's SVN repository. View the ASF docs for more
   information.
+
+
+## Merging DB migrations
+
+When 2 db migrations collide, you'll get an error message like this one:
+
+```
+  alembic.util.exc.CommandError: Multiple head revisions are present for
+  given argument 'head'; please specify a specific target
+  revision, '<branchname>@head' to narrow to a specific head,
+  or 'heads' for all heads`
+```
+
+To fix it, first run `superset db heads`, this should list 2 or more
+migration hashes. Then run
+`superset db merge {PASTE_SHA1_HERE} {PASTE_SHA2_HERE}`. This will create
+a new merge migration. You can then `superset db upgrade` to this new
+checkpoint.

UPDATING.md

@@ -3,6 +3,20 @@
 This file documents any backwards-incompatible changes in Superset and
 assists people when migrating to a new version.
 
+## Superset 0.27.0
+* Superset 0.27 start to use nested layout for dashboard builder, which is not 
+backward-compatible with earlier dashboard grid data. We provide migration script
+to automatically convert dashboard grid to nested layout data. To be safe, please 
+take a database backup prior to this upgrade. It's the only way people could go 
+back to a previous state.
+
+
+## Superset 0.26.0
+* Superset 0.26.0 deprecates the `superset worker` CLI, which is a simple
+wrapper around the `celery worker` command, forcing you into crafting
+your own native `celery worker` command. Your command should look something
+like `celery worker --app=superset.sql_lab:celery_app --pool=gevent -Ofair`
+
 ## Superset 0.25.0
 Superset 0.25.0 contains a backwards incompatible changes.
 If you run a production system you should schedule downtime for this