The App Engine datastore uses indexes for every query your application makes. These indexes are updated whenever an entity changes, so the results can be returned quickly when the app makes a query. To do this, the datastore needs to know in advance which queries the application will make. You specify which indexes your app needs in a configuration file. The development server can generate the datastore index configuration automatically as you test your app.
Every datastore query made by an application needs a corresponding index. Indexes for simple queries, such as queries over a single property, are created automatically. Indexes for complex queries must be defined in a configuration file named
index.yaml. This file is stored in the application's
WEB-INF directory to create indexes in the datastore.
If a query needs an index that does not have an appropriate entry in the configuration file, the development web server automatically adds items to this file when the application tries to execute the query. You can adjust indexes or create new ones manually by editing the file.
Tip: If, during testing, the app exercises every query it will make using the development web server, then the generated entries in
index.yaml will be complete. You only need to edit the file manually to delete indexes that are no longer used, or to define indexes not created by the development web server.
For more information about indexes, see the Datastore Indexes page.
The following is an example of an
indexes: - kind: Cat ancestor: no properties: - name: name - name: age direction: desc - kind: Cat properties: - name: name direction: asc - name: whiskers direction: desc - kind: Store ancestor: yes properties: - name: business direction: asc - name: owner direction: asc
The syntax of
index.yaml is the YAML format. For more information about this syntax, see the YAML website for more information.
Tip: The YAML format supports comments. A line that begins with a pound (
#) character is ignored:
# This is a comment.
index.yaml has a single list element called
indexes. Each element in the list represents an index for the application.
An index element can have the following elements:
The kind of the entity for the query. The kind attribute specifies the kind of the entities to index.
A list of properties to include as columns of the index, in the order to be sorted: properties used in equality filters first, followed by the property used in inequality filters, then the sort orders and their directions.
Each element in this list has the following elements:
The datastore name of the property.
The direction to sort, either
ascfor ascending or
descfor descending. This is only required for properties used in sort orders of the query, and must match the direction used by the query. The default is
The ancestor attribute is
trueif the index supports a query that filters entities by the entity group parent,
Determining the indexes required by your application's queries manually can be tedious and error-prone. Thankfully, when you use
index.yaml, the development server automatically determines the index configuration for you.
The development server maintains the auto-generated index in a file named
datastore-indexes-auto.xml in the directory
WEB-INF/appengine-generated/ in your application's WAR. AppCfg uses both
datastore-indexes-auto.xml to determine which indexes need to be built for your app on App Engine.
If you have an app running in the development server, and it attempts a datastore query for which there is no corresponding index in either
datastore-indexes-auto.xml, then the server adds the appropriate configuration to