The BatchWriteItem
operation puts or deletes multiple items
in one or more tables. A single call to BatchWriteItem
can
write up to 16 MB of data, which can comprise as many as 25 put or delete
requests. Individual items to be written can be as large as 400 KB.
BatchWriteItem
cannot update items. To update items, use the
UpdateItem
action.
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.
Note that if none of the items can be processed due to
insufficient provisioned throughput on all of the tables in the request,
then BatchWriteItem
will return a
ProvisionedThroughputExceededException
.
If DynamoDB returns any unprocessed items, you should retry the batch
operation on those items. However, we strongly recommend that you use
an exponential backoff algorithm. If you retry the batch operation
immediately, the underlying read or write requests can still fail due to
throttling on the individual tables. If you delay the batch operation
using exponential backoff, the individual requests in the batch are much
more likely to succeed.
For more information, see Batch Operations and Error Handling in the Amazon DynamoDB
Developer Guide.
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 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, 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, you must update or delete the specified items one at a time.
In both situations, BatchWriteItem
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, 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.
-
Your request contains at least two items with identical hash and range
keys (which essentially is two put operations).
-
There are more than 25 requests in the batch.
-
Any individual item in a batch exceeds 400 KB.
-
The total request size exceeds 16 MB.