Batch Get Item
| dynamodb_batch_get_item | R Documentation |
The BatchGetItem operation returns the attributes of one or more items from one or more tables¶
Description¶
The batch_get_item 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 16 MB of data, which can contain
as many as 100 items. batch_get_item returns a partial result if the
response size limit is exceeded, the table's provisioned throughput is
exceeded, more than 1MB per partition is requested, 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.
If you request more than 100 items, batch_get_item returns a
ValidationException with the message "Too many items requested for the
BatchGetItem call."
For example, if you ask to retrieve 100 items, but each individual item
is 300 KB in size, the system returns 52 items (so as not to exceed the
16 MB limit). It also returns 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 none of the items can be processed due to insufficient provisioned
throughput on all of the tables in the request, then batch_get_item
returns a ProvisionedThroughputExceededException. If at least one of
the items is successfully processed, then batch_get_item completes
successfully, while returning the keys of the unread items in
UnprocessedKeys.
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.
By default, batch_get_item 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, batch_get_item may retrieve
items in parallel.
When designing your application, keep in mind that DynamoDB does not
return items in any particular order. To help parse the response by
item, include the primary key values for the items in your request in
the ProjectionExpression 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 Working with Tables in the Amazon DynamoDB Developer Guide.
Usage¶
dynamodb_batch_get_item(RequestItems, ReturnConsumedCapacity)
Arguments¶
RequestItems |
[required] A map of one or more table names or table ARNs and,
for each table, a map that describes one or more items to retrieve from
that table. Each table name or ARN can be used only once per
Each element in the map of items to retrieve consists of the following:
|
ReturnConsumedCapacity |
Value¶
A list with the following syntax:
list(
Responses = list(
list(
list(
list(
S = "string",
N = "string",
B = raw,
SS = list(
"string"
),
NS = list(
"string"
),
BS = list(
raw
),
M = list(
list()
),
L = list(
list()
),
NULL = TRUE|FALSE,
BOOL = TRUE|FALSE
)
)
)
),
UnprocessedKeys = list(
list(
Keys = list(
list(
list(
S = "string",
N = "string",
B = raw,
SS = list(
"string"
),
NS = list(
"string"
),
BS = list(
raw
),
M = list(
list()
),
L = list(
list()
),
NULL = TRUE|FALSE,
BOOL = TRUE|FALSE
)
)
),
AttributesToGet = list(
"string"
),
ConsistentRead = TRUE|FALSE,
ProjectionExpression = "string",
ExpressionAttributeNames = list(
"string"
)
)
),
ConsumedCapacity = list(
list(
TableName = "string",
CapacityUnits = 123.0,
ReadCapacityUnits = 123.0,
WriteCapacityUnits = 123.0,
Table = list(
ReadCapacityUnits = 123.0,
WriteCapacityUnits = 123.0,
CapacityUnits = 123.0
),
LocalSecondaryIndexes = list(
list(
ReadCapacityUnits = 123.0,
WriteCapacityUnits = 123.0,
CapacityUnits = 123.0
)
),
GlobalSecondaryIndexes = list(
list(
ReadCapacityUnits = 123.0,
WriteCapacityUnits = 123.0,
CapacityUnits = 123.0
)
)
)
)
)
Request syntax¶
svc$batch_get_item(
RequestItems = list(
list(
Keys = list(
list(
list(
S = "string",
N = "string",
B = raw,
SS = list(
"string"
),
NS = list(
"string"
),
BS = list(
raw
),
M = list(
list()
),
L = list(
list()
),
NULL = TRUE|FALSE,
BOOL = TRUE|FALSE
)
)
),
AttributesToGet = list(
"string"
),
ConsistentRead = TRUE|FALSE,
ProjectionExpression = "string",
ExpressionAttributeNames = list(
"string"
)
)
),
ReturnConsumedCapacity = "INDEXES"|"TOTAL"|"NONE"
)
Examples¶
## Not run:
# This example reads multiple items from the Music table using a batch of
# three GetItem requests. Only the AlbumTitle attribute is returned.
svc$batch_get_item(
RequestItems = list(
Music = list(
Keys = list(
list(
Artist = list(
S = "No One You Know"
),
SongTitle = list(
S = "Call Me Today"
)
),
list(
Artist = list(
S = "Acme Band"
),
SongTitle = list(
S = "Happy Day"
)
),
list(
Artist = list(
S = "No One You Know"
),
SongTitle = list(
S = "Scared of My Shadow"
)
)
),
ProjectionExpression = "AlbumTitle"
)
)
)
## End(Not run)