API Version: 2013-12-02

This operation returns a shard iterator in ShardIterator. The shard iterator specifies the position in the shard from which you want to start reading data records sequentially. A shard iterator specifies this position using the sequence number of a data record in a shard. A sequence number is the identifier associated with every record ingested in the Amazon Kinesis stream. The sequence number is assigned by the Amazon Kinesis service when a record is put into the stream.

You must specify the shard iterator type in the GetShardIterator request. For example, you can set the ShardIteratorType parameter to read exactly from the position denoted by a specific sequence number by using the AT_SEQUENCE_NUMBER shard iterator type, or right after the sequence number by using the AFTER_SEQUENCE_NUMBER shard iterator type, using sequence numbers returned by earlier PutRecord, GetRecords or DescribeStream requests. You can specify the shard iterator type TRIM_HORIZON in the request to cause ShardIterator to point to the last untrimmed record in the shard in the system, which is the oldest data record in the shard. Or you can point to just after the most recent record in the shard, by using the shard iterator type LATEST, so that you always read the most recent data in the shard.

Note: Each shard iterator expires five minutes after it is returned to the requester.

When you repeatedly read from an Amazon Kinesis stream use a GetShardIterator request to get the first shard iterator to to use in your first GetRecords request and then use the shard iterator returned by the GetRecords request in NextShardIterator for subsequent reads. A new shard iterator is returned by every GetRecords request in NextShardIterator, which you use in the ShardIterator parameter of the next GetRecords request.

If a GetShardIterator request is made too often, you will receive a ProvisionedThroughputExceededException. For more information about throughput limits, see the Amazon Kinesis Developer Guide.

GetShardIterator can return null for its ShardIterator to indicate that the shard has been closed and that the requested iterator will return no more data. A shard can be closed by a SplitShard or MergeShards operation.

GetShardIterator has a limit of 5 transactions per second per account per open shard.

http://docs.aws.amazon.com/kinesis/2013-12-02/APIReference/API_GetShardIterator.html