IAmazonDynamoDB Interface

The BatchGetItem operation returns the attributes of one or more items from one or more tables. You identify requested items by primary key.

A single operation can retrieve up to 1 MB of data, which can comprise as many as 100 items. BatchGetItem will return a partial result if the response size limit is exceeded, the table's provisioned throughput is exceeded, or an internal processing failure occurs. If a partial result is returned, the operation returns a value for UnprocessedKeys . You can use this value to retry the operation starting with the next item to get.

For example, if you ask to retrieve 100 items, but each individual item is 50 KB in size, the system returns 20 items (1 MB) and an appropriate UnprocessedKeys value so you can get the next page of results. If desired, your application can include its own logic to assemble the pages of results into one dataset.

If no items can be processed because of insufficient provisioned throughput on each of the tables involved in the request, BatchGetItem throws ProvisionedThroughputExceededException .

By default, BatchGetItem performs eventually consistent reads on every table in the request. If you want strongly consistent reads instead, you can set ConsistentRead to true for any or all tables.

In order to minimize response latency, BatchGetItem fetches items in parallel.

When designing your application, keep in mind that Amazon DynamoDB does not return attributes in any particular order. To help parse the response by item, include the primary key values for the items in your request in the AttributesToGet parameter.

If a requested item does not exist, it is not returned in the result. Requests for nonexistent items consume the minimum read capacity units according to the type of read. For more information, see Capacity Units Calculations in the Amazon DynamoDB Developer Guide.

The BatchWriteItem operation puts or deletes multiple items in one or more tables. A single call to BatchWriteItem can write up to 1 MB of data, which can comprise as many as 25 put or delete requests. Individual items to be written can be as large as 64 KB.

NOTE: BatchWriteItem cannot update items. To update items, use the UpdateItem API.

The individual PutItem and DeleteItem operations specified in BatchWriteItem are atomic; however BatchWriteItem as a whole is not. If any requested operations fail because the table's provisioned throughput is exceeded or an internal processing failure occurs, the failed operations are returned in the UnprocessedItems response parameter. You can investigate and optionally resend the requests. Typically, you would call BatchWriteItem in a loop. Each iteration would check for unprocessed items and submit a new BatchWriteItem request with those unprocessed items until all items have been processed.

To write one item, you can use the PutItem operation; to delete one item, you can use the DeleteItem operation.

With BatchWriteItem , you can efficiently write or delete large amounts of data, such as from Amazon Elastic MapReduce (EMR), or copy data from another database into Amazon DynamoDB. In order to improve performance with these large-scale operations, BatchWriteItem does not behave in the same way as individual PutItem and DeleteItem calls would For example, you cannot specify conditions on individual put and delete requests, and BatchWriteItem does not return deleted items in the response.

If you use a programming language that supports concurrency, such as Java, you can use threads to write items in parallel. Your application must include the necessary logic to manage the threads.

With languages that don't support threading, such as PHP, BatchWriteItem will write or delete the specified items one at a time. In both situations, BatchWriteItem provides an alternative where the API performs the specified put and delete operations in parallel, giving you the power of the thread pool approach without having to introduce complexity into your application.

Parallel processing reduces latency, but each specified put and delete request consumes the same number of write capacity units whether it is processed in parallel or not. Delete operations on nonexistent items consume one write capacity unit.

If one or more of the following is true, Amazon DynamoDB rejects the entire batch write operation:

• One or more tables specified in the BatchWriteItem request does not exist.

• Primary key attributes specified on an item in the request do not match those in the corresponding table's primary key schema.

• You try to perform multiple operations on the same item in the same BatchWriteItem request. For example, you cannot put and delete the same item in the same BatchWriteItem request.

• The total request size exceeds 1 MB.

• Any individual item in a batch exceeds 64 KB.

The CreateTable operation adds a new table to your account. In an AWS account, table names must be unique within each region. That is, you can have two tables with same name if you create the tables in different regions.

CreateTable is an asynchronous operation. Upon receiving a CreateTable request, Amazon DynamoDB immediately returns a response with a TableStatus of CREATING . After the table is created, Amazon DynamoDB sets the TableStatus to ACTIVE . You can perform read and write operations only on an ACTIVE table.

If you want to create multiple tables with local secondary indexes on them, you must create them sequentially. Only one table with local secondary indexes can be in the CREATING state at any given time.

You can use the DescribeTable API to check the table status.

Deletes a single item in a table by primary key. You can perform a conditional delete operation that deletes the item if it exists, or if it has an expected attribute value.

In addition to deleting an item, you can also return the item's attribute values in the same operation, using the ReturnValues parameter.

Unless you specify conditions, the DeleteItem is an idempotent operation; running it multiple times on the same item or attribute does not result in an error response.

Conditional deletes are useful for only deleting items if specific conditions are met. If those conditions are met, Amazon DynamoDB performs the delete. Otherwise, the item is not deleted.

The DeleteTable operation deletes a table and all of its items. After a DeleteTable request, the specified table is in the DELETING state until Amazon DynamoDB completes the deletion. If the table is in the ACTIVE state, you can delete it. If a table is in CREATING or UPDATING states, then Amazon DynamoDB returns a ResourceInUseException . If the specified table does not exist, Amazon DynamoDB returns a ResourceNotFoundException . If table is already in the DELETING state, no error is returned.

NOTE: Amazon DynamoDB might continue to accept data read and write operations, such as GetItem and PutItem, on a table in the DELETING state until the table deletion is complete.

When you delete a table, any local secondary indexes on that table are also deleted.

Use the DescribeTable API to check the status of the table.

Returns information about the table, including the current status of the table, when it was created, the primary key schema, and any indexes on the table.

The GetItem operation returns a set of attributes for the item with the given primary key. If there is no matching item, GetItem does not return any data.

GetItem provides an eventually consistent read by default. If your application requires a strongly consistent read, set ConsistentRead to true . Although a strongly consistent read might take more time than an eventually consistent read, it always returns the last updated value.

Returns an array of all the tables associated with the current account and endpoint.

Returns an array of all the tables associated with the current account and endpoint.

Creates a new item, or replaces an old item with a new item. If an item already exists in the specified table with the same primary key, the new item completely replaces the existing item. You can perform a conditional put (insert a new item if one with the specified primary key doesn't exist), or replace an existing item if it has certain attribute values.

In addition to putting an item, you can also return the item's attribute values in the same operation, using the ReturnValues parameter.

When you add an item, the primary key attribute(s) are the only required attributes. Attribute values cannot be null. String and binary type attributes must have lengths greater than zero. Set type attributes cannot be empty. Requests with empty values will be rejected with a ValidationException .

You can request that PutItem return either a copy of the old item (before the update) or a copy of the new item (after the update). For more information, see the ReturnValues description.

NOTE: To prevent a new item from replacing an existing item, use a conditional put operation with Exists set to false for the primary key attribute, or attributes.

For more information about using this API, see Working with Items in the Amazon DynamoDB Developer Guide.

A Query operation directly accesses items from a table using the table primary key, or from an index using the index key. You must provide a specific hash key value. You can narrow the scope of the query by using comparison operators on the range key value, or on the index key. You can use the ScanIndexForward parameter to get results in forward or reverse order, by range key or by index key.

Queries that do not return results consume the minimum read capacity units according to the type of read.

If the total number of items meeting the query criteria exceeds the result set size limit of 1 MB, the query stops and results are returned to the user with a LastEvaluatedKey to continue the query in a subsequent operation. Unlike a Scan operation, a Query operation never returns an empty result set and a LastEvaluatedKey . The LastEvaluatedKey is only provided if the results exceed 1 MB, or if you have used Limit .

To request a strongly consistent result, set ConsistentRead to true.

The Scan operation returns one or more items and item attributes by accessing every item in the table. To have Amazon DynamoDB return fewer items, you can provide a ScanFilter .

If the total number of scanned items exceeds the maximum data set size limit of 1 MB, the scan stops and results are returned to the user with a LastEvaluatedKey to continue the scan in a subsequent operation. The results also include the number of items exceeding the limit. A scan can result in no table data meeting the filter criteria.

The result set is eventually consistent.

By default, Scan operations proceed sequentially; however, for faster performance on large tables, applications can request a parallel Scan by specifying the Segment and TotalSegments parameters. For more information, see Parallel Scan in the Amazon DynamoDB Developer Guide.

Edits an existing item's attributes, or inserts a new item if it does not already exist. You can put, delete, or add attribute values. You can also perform a conditional update (insert a new attribute name-value pair if it doesn't exist, or replace an existing name-value pair if it has certain expected attribute values).

In addition to updating an item, you can also return the item's attribute values in the same operation, using the ReturnValues parameter.

Updates the provisioned throughput for the given table. Setting the throughput for a table helps you manage performance and is part of the provisioned throughput feature of Amazon DynamoDB.

The provisioned throughput values can be upgraded or downgraded based on the maximums and minimums listed in the Limits section in the Amazon DynamoDB Developer Guide.

The table must be in the ACTIVE state for this operation to succeed. UpdateTable is an asynchronous operation; while executing the operation, the table is in the UPDATING state. While the table is in the UPDATING state, the table still has the provisioned throughput from before the call. The new provisioned throughput setting is in effect only when the table returns to the ACTIVE state after the UpdateTable operation.

You cannot add, modify or delete local secondary indexes using UpdateTable . Local secondary indexes can only be defined at table creation time.