Gets data records from a Kinesis data stream's shard.

When invoking this API, it is recommended you use the StreamARN input parameter in addition to the ShardIterator parameter.

Specify a shard iterator using the ShardIterator parameter. The shard iterator specifies the position in the shard from which you want to start reading data records sequentially. If there are no records available in the portion of the shard that the iterator points to, GetRecords returns an empty list. It might take multiple calls to get to a portion of the shard that contains records.

You can scale by provisioning multiple shards per stream while considering service limits (for more information, see Amazon Kinesis Data Streams Limits in the Amazon Kinesis Data Streams Developer Guide). Your application should have one thread per shard, each reading continuously from its stream. To read from a stream continually, call GetRecords in a loop. Use GetShardIterator to get the shard iterator to specify in the first GetRecords call. GetRecords returns a new shard iterator in NextShardIterator. Specify the shard iterator returned in NextShardIterator in subsequent calls to GetRecords. If the shard has been closed, the shard iterator can't return more data and GetRecords returns null in NextShardIterator. You can terminate the loop when the shard is closed, or when the shard iterator reaches the record with the sequence number or other attribute that marks it as the last record to process.

Each data record can be up to 1 MiB in size, and each shard can read up to 2 MiB per second. You can ensure that your calls don't exceed the maximum supported size or throughput by using the Limit parameter to specify the maximum number of records that GetRecords can return. Consider your average record size when determining this limit. The maximum number of records that can be returned per call is 10,000.

The size of the data returned by GetRecords varies depending on the utilization of the shard. It is recommended that consumer applications retrieve records via the GetRecords command using the 5 TPS limit to remain caught up. Retrieving records less frequently can lead to consumer applications falling behind. The maximum size of data that GetRecords can return is 10 MiB. If a call returns this amount of data, subsequent calls made within the next 5 seconds throw ProvisionedThroughputExceededException. If there is insufficient provisioned throughput on the stream, subsequent calls made within the next 1 second throw ProvisionedThroughputExceededException. GetRecords doesn't return any data when it throws an exception. For this reason, we recommend that you wait 1 second between calls to GetRecords. However, it's possible that the application will get exceptions for longer than 1 second.

To detect whether the application is falling behind in processing, you can use the MillisBehindLatest response attribute. You can also monitor the stream using CloudWatch metrics and other mechanisms (see Monitoring in the Amazon Kinesis Data Streams Developer Guide).

Each Amazon Kinesis record includes a value, ApproximateArrivalTimestamp, that is set when a stream successfully receives and stores a record. This is commonly referred to as a server-side time stamp, whereas a client-side time stamp is set when a data producer creates or sends the record to a stream (a data producer is any data source putting data records into a stream, for example with PutRecords). The time stamp has millisecond precision. There are no guarantees about the time stamp accuracy, or that the time stamp is always increasing. For example, records in a shard or across a stream might have time stamps that are out of order.

This operation has a limit of five transactions per second per shard.