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The most obvious use case is data import. A developer looking to import large amounts of data would take the following steps: Create a CSV file containing the data you want to import. The assumption here is that each line of data corresponds to a datastore entity you want to create Upload the CSV file to the blobstore. You’ll need billing to be enabled for this to work. Create your Mapper, push it live and run your job importing your data. This isn’t meant to be a replacement for the bulk uploader tool; merely an alternative. This method requires a good amount more programmatic changes for custom data transforms. The advantage of this method is that the work is done on the server side, whereas the bulk uploader makes use of the remote API to get work done. Let’s get started on each of the steps.

to build Mappers that map across some large, contiguous piece of data as opposed to Entities in the datastore

you can only expect to update any single entity or entity group about five times a second. That is an estimate and the actual update rate for an entity is dependent on several attributes of the entity, including how many properties it has, how large it is, and how many indexes need updating. While a single entity or entity group has a limit on how quickly it can be updated, App Engine excels at handling many parallel requests distributed across distinct entities, and we can take advantage of this by using sharding.

Just set up remote_api for your app using the directions here - notably the tip: Tip: If you have a Java app, you can use the Python bulkloader.py tool by installing the Java version of the remote_api handler, which is included with the Java runtime environment. The handler servlet class is com.google.apphosting.utils.remoteapi.RemoteApiServlet. Then, use the Python bulkloader with --dump or --restore.

Now you can choose to put this in an existing version of your applications config.ru. Or you can choose to put it in a new version (ie. version just for bulk upload/download without your application code). Either way once a version with the RemoteApiServlet is uploaded run this command to download your data: bulkloader.py --dump --app_id="application id" --url="url_to_remote_api_servlet" --filename="file to download data to" Here is an example from one of my apps: bulkloader.py --dump --app_id=jsm277 --url=http://bulkmove.latest.jsm277.appspot.com/remote_api --filename=test_download_data This command will download every object in your applications Datastore. If you only want to download the objects of one kind then simple add the --kind= option. Another example: bulkloader.py --dump --app_id=jsm277 --url=http://bulkmove.latest.jsm277.appspot.com/remote_api --filename=test_download_data --kind=Posts In order to restore the data that you have just downloaded use this command: bulkloader.py --restore --url="url_to_remote_api_servlet" --filename="file name from dump command" --app_id="application id" Here is an example command: bulkloader.py --restore --url=http://bulkmove.latest.railsturbinetest.appspot.com/remote_api --filename=test_download_data --app_id=railsturbinetest There are several important thing to keep in mind when restoring the Datastore objectes. The restore command simple restores whatever is in the filename that you provide. So it does not matter if you dump your entire Datastore or just one kind you use the same command to restore them both. You can restore Datastore objects to a different application then the one that they were downloaded from. However, is important to keep in mind that the object's key is used to restore each object. So if there already esists an object in the Datastore with the same key as an object that is being restored the object in the Datastore will be overwritten The bulkloader.py is a good tool for moving data between applications on the Google App Engine and for locally backing up your data. However, it is not good for data conversion or manipulation in anyway since the data is stored in a binary form. So happy data moving.

Tip: If you have a Java app, you can use the Python bulkloader.py tool by installing the Java version of the remote_api handler, which is included with the Java runtime environment. The handler servlet class is com.google.apphosting.utils.remoteapi.RemoteApiServlet.