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Running the Datastore Emulator | Cloud Datastore Documentation

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The Datastore emulator provides local emulation of the production Datastore environment. You can use the emulator to develop and test your application locally. In addition, the emulator can help you generate indexes for your production Datastore instance and delete unneeded indexes. This page guides you through installing the emulator, starting the emulator, and setting environment variables to connect your application to the emulator.

By default, the Datastore emulator does not emulate features introduced by Firestore in Datastore mode. The following default emulator behaviors do not match Datastore mode:

• The emulator simulates eventual consistency, by default. Firestore in Datastore mode is strongly consistent.
• The emulator does not allow non-ancestor queries within transactions. Firestore in Datastore mode no longer has this limitation.
• The emulator does not support IN, !=, and NOT-IN queries.
• The emulator does not support aggregation queries like COUNT(*).

However, the --use-firestore-in-datastore-mode flag helps loosen some of the restrictions above for Firestore in Datastore Mode.

• The emulator simulates strongly consistent non-ancestor queries.
• The emulator allows for non-ancestor queries within transactions.
• The emulator removes the limitation of 25 entity groups in a transaction.

To emulate Firestore in Datastore mode, use gcloud emulators firestore start --database-mode=datastore-mode instead.

To use the Datastore emulator you need:

• A Java JRE (version 21 or greater)
• The Google Cloud CLI
• An application built using the Google Cloud Client Libraries

The Datastore emulator is a component of the gcloud CLI. Use the gcloud components install command to install the Datastore emulator:

gcloud components install cloud-datastore-emulator

The emulator simulates Datastore by creating /WEB-INF/appengine-generated/local_db.bin in a specified data directory and storing data in local_db.bin. By default, the emulator uses the data directory ~/.config/gcloud/emulators/datastore/. The local_db.bin file persists between sessions of the emulator. You can set up multiple data directories and think of each as a separate, local Datastore mode instance. To clear the contents of a local_db.bin file, stop the emulator and manually delete the file.

Start the emulator by executing datastore start from a command prompt:

gcloud beta emulators datastore start [flags]

where [flags] are optional command-line arguments supplied to the gcloud CLI. For example:

• --data-dir=[DATA_DIR] changes the emulator's data directory. The emulator creates the /WEB-INF/appengine-generated/local_db.bin file inside [DATA_DIR] or, if available, uses an existing file.

• --no-store-on-disk configures the emulator not to persist any data to disk for the emulator session.

See the gcloud beta emulators datastore start reference for the full list of optional flags.

After you start the emulator, you should see a message similar to the following:

...
[datastore] Dev App Server is now running.

To stop the emulator, type Control-C at the command prompt.

After you start the emulator, you need to set environment variables so that your application connects to the emulator instead of your production Datastore mode database. Set these environment variables on the same machine that you use to run your application.

You need to set the environment variables each time you start the emulator. The environment variables depend on dynamically assigned port numbers that could change when you restart the emulator.

If your application and the emulator run on the same machine, you can set the environment variables automatically:

Run env-init using command substitution:

$(gcloud beta emulators datastore env-init)

Create and run a batch file using output from env-init:

gcloud beta emulators datastore env-init > set_vars.cmd && set_vars.cmd

Your application will now connect to the Datastore emulator.

If your application and the emulator run on different machines, set the environment variables manually:

1. Run the env-init command:

   gcloud beta emulators datastore env-init

2. On the machine that runs your application, set the environment variables and values as directed by the output of the env-init command. For example:

   Linux / macOS

   export DATASTORE_DATASET=my-project-id
   export DATASTORE_EMULATOR_HOST=::1:8432
   export DATASTORE_EMULATOR_HOST_PATH=::1:8432/datastore
   export DATASTORE_HOST=http://::1:8432
   export DATASTORE_PROJECT_ID=my-project-id

   Windows

   set DATASTORE_DATASET=my-project-id
   set DATASTORE_EMULATOR_HOST=::1:8432
   set DATASTORE_EMULATOR_HOST_PATH=::1:8432/datastore
   set DATASTORE_HOST=http://::1:8432
   set DATASTORE_PROJECT_ID=my-project-id

Your application will now connect to the Datastore emulator. Note that the project id and port provided by the command will differ from the above example.

By running your application using the emulator, you can generate indexes for your production Datastore mode database, as well as delete unneeded indexes. Learn more at Using the gcloud CLI.

After you finish using the emulator, stop the emulator (Control-C) and remove the environment variables so your application will connect to your production Datastore mode database.

If your application and the emulator run on the same machine, you can remove the environment variables automatically:

Run env-unset using command substitution:

$(gcloud beta emulators datastore env-unset)

Create and run a batch file using output from env-unset:

gcloud beta emulators datastore env-unset > remove_vars.cmd && remove_vars.cmd

Your application will now connect to your production Datastore mode database.

If your application and the emulator run on different machines, remove the environment variables manually:

1. Run the env-unset command:

   gcloud beta emulators datastore env-unset

2. On the machine that runs your application, remove the environment variables as directed by the output of the env-unset command. For example:

   Linux / macOS

   unset DATASTORE_DATASET
   unset DATASTORE_EMULATOR_HOST
   unset DATASTORE_EMULATOR_HOST_PATH
   unset DATASTORE_HOST
   unset DATASTORE_PROJECT_ID

   Windows

   set DATASTORE_DATASET=
   set DATASTORE_EMULATOR_HOST=
   set DATASTORE_EMULATOR_HOST_PATH=
   set DATASTORE_HOST=
   set DATASTORE_PROJECT_ID=

Your application will now connect to your production Datastore mode database.

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2025-08-07 UTC.

[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-07 UTC."],[[["The Datastore emulator allows for local development and testing, simulating the production Datastore environment."],["The emulator can be installed via the `gcloud components install cloud-datastore-emulator` command and requires Java JRE 11 or greater and the Google Cloud CLI."],["To start the emulator, use `gcloud emulators datastore start`, and environment variables need to be set for applications to connect to it, either automatically or manually."],["The emulator has behaviors that differ from Firestore in Datastore mode, such as simulating eventual consistency, however, some restrictions can be loosened with the `--use-firestore-in-datastore-mode` flag, and `gcloud emulators firestore start --database-mode=datastore-mode` should be used to properly emulate it."],["After finishing with the emulator, environment variables must be removed for the application to reconnect to the production Datastore database."]]],[]]

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