Amazon DynamoDB
Developer Guide (API Version 2012-08-10)

DynamoDB Usage Notes

Except for the endpoint, applications that run with the downloadable version of Amazon DynamoDB should also work with the DynamoDB web service. However, when using DynamoDB locally, you should be aware of the following:

  • If you use the -sharedDb option, DynamoDB creates a single database file named shared-local-instance.db. Every program that connects to DynamoDB accesses this file. If you delete the file, you lose any data that you have stored in it.

  • If you omit -sharedDb, the database file is named myaccesskeyid_region.db, with the AWS access key ID and Region as they appear in your application configuration. If you delete the file, you lose any data that you have stored in it.

  • If you use the -inMemory option, DynamoDB doesn't write any database files at all. Instead, all data is written to memory, and the data is not saved when you terminate DynamoDB.

  • If you use the -optimizeDbBeforeStartup option, you must also specify the -dbPath parameter so that DynamoDB can find its database file.

  • The AWS SDKs for DynamoDB require that your application configuration specify an access key value and an AWS Region value. Unless you're using the -sharedDb or the -inMemory option, DynamoDB uses these values to name the local database file.

    These values don't have to be valid AWS values to run locally. However, you might find it convenient to use valid values so that you can run your code in the cloud later simply by changing the endpoint you're using.

Command Line Options

You can use the following command line options with the downloadable version of DynamoDB:

  • -cors value — Enables support for cross-origin resource sharing (CORS) for JavaScript. You must provide a comma-separated "allow" list of specific domains. The default setting for -cors is an asterisk (*), which allows public access.

  • -dbPath value — The directory where DynamoDB writes its database file. If you don't specify this option, the file is written to the current directory. You can't specify both -dbPath and -inMemory at once.

  • -delayTransientStatuses — Causes DynamoDB to introduce delays for certain operations. DynamoDB (Downloadable Version) can perform some tasks almost instantaneously, such as create/update/delete operations on tables and indexes. However, the DynamoDB service requires more time for these tasks. Setting this parameter helps DynamoDB running on your computer simulate the behavior of the DynamoDB web service more closely. (Currently, this parameter introduces delays only for global secondary indexes that are in either CREATING or DELETING status.)

  • -help — Prints a usage summary and options.

  • -inMemory — DynamoDB runs in memory instead of using a database file. When you stop DynamoDB, none of the data is saved. You can't specify both -dbPath and -inMemory at once.

  • -optimizeDbBeforeStartup — Optimizes the underlying database tables before starting DynamoDB on your computer. You also must specify -dbPath when you use this parameter.

  • -port value — The port number that DynamoDB uses to communicate with your application. If you don't specify this option, the default port is 8000.

    Note

    DynamoDB uses port 8000 by default. If port 8000 is unavailable, this command throws an exception. You can use the -port option to specify a different port number. For a complete list of DynamoDB runtime options, including -port , type this command:

    java -Djava.library.path=./DynamoDBLocal_lib -jar DynamoDBLocal.jar -help

  • -sharedDb — If you specify -sharedDb, DynamoDB uses a single database file instead of separate files for each credential and Region.

Setting the Local Endpoint

By default, the AWS SDKs and tools use endpoints for the Amazon DynamoDB web service. To use the SDKs and tools with the downloadable version of DynamoDB, you must specify the local endpoint:

http://localhost:8000

AWS Command Line Interface

You can use the AWS Command Line Interface (AWS CLI) to interact with downloadable DynamoDB. For example, you can use it to perform all the steps in Creating Tables and Loading Sample Data.

To access DynamoDB running locally, use the --endpoint-url parameter. The following is an example of using the AWS CLI to list the tables in DynamoDB on your computer:

aws dynamodb list-tables --endpoint-url http://localhost:8000

Note

The AWS CLI can't use the downloadable version of DynamoDB as a default endpoint. Therefore, you must specify --endpoint-url with each AWS CLI command.

AWS SDKs

The way you specify an endpoint depends on the programming language and AWS SDK you're using. The following sections describe how to do this:

Note

For examples in other programming languages, see Getting Started with DynamoDB.

Differences Between Downloadable DynamoDB and the DynamoDB Web Service

The downloadable version of DynamoDB is intended for development and testing purposes only. By comparison, the DynamoDB web service is a managed service with scalability, availability, and durability features that make it ideal for production use.

The downloadable version of DynamoDB differs from the web service in the following ways:

  • Regions and distinct AWS accounts are not supported at the client level.

  • Provisioned throughput settings are ignored in downloadable DynamoDB, even though the CreateTable operation requires them. For CreateTable, you can specify any numbers you want for provisioned read and write throughput, even though these numbers are not used. You can call UpdateTable as many times as you want per day. However, any changes to provisioned throughput values are ignored.

  • Scan operations are performed sequentially. Parallel scans are not supported. The Segment and TotalSegments parameters of the Scan operation are ignored.

  • The speed of read and write operations on table data is limited only by the speed of your computer. CreateTable, UpdateTable, and DeleteTable operations occur immediately, and table state is always ACTIVE. UpdateTable operations that change only the provisioned throughput settings on tables or global secondary indexes occur immediately. If an UpdateTable operation creates or deletes any global secondary indexes, then those indexes transition through normal states (such as CREATING and DELETING, respectively) before they become an ACTIVE state. The table remains ACTIVE during this time.

  • Read operations are eventually consistent. However, due to the speed of DynamoDB running on your computer, most reads appear to be strongly consistent.

  • Consumed capacity units are not tracked. In operation responses, nulls are returned instead of capacity units.

  • Item collection metrics and item collection sizes are not tracked. In operation responses, nulls are returned instead of item collection metrics.

  • In DynamoDB, there is a 1 MB limit on data returned per result set. Both the DynamoDB web service and the downloadable version enforce this limit. However, when querying an index, the DynamoDB service calculates only the size of the projected key and attributes. By contrast, the downloadable version of DynamoDB calculates the size of the entire item.

  • If you're using DynamoDB Streams, the rate at which shards are created might differ. In the DynamoDB web service, shard-creation behavior is partially influenced by table partition activity. When you run DynamoDB locally, there is no table partitioning. In either case, shards are ephemeral, so your application should not be dependent on shard behavior.