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# Shard Iterator Expires Unexpectedly
* A **shard is a uniquely identified sequence of data records in a stream**.
* A **stream is composed of one or more shards**, each of which provides a fixed unit of capacity.
* A **new shard iterator is returned by every GetRecords request (as `NextShardIterator`)**.
* You then **use in the next GetRecords request (as `ShardIterator`)**.
* **Typically, this shard iterator does not expire before you use it**.
* However, you **may find that shard iterators expire because you have not called GetRecords for more than 5 minutes**, or **because you've performed a restart of your consumer application**.
* If the shard iterator expires immediately, before you can use it, this **might indicate that the DynamoDB table used by Kinesis does not have enough capacity to store the lease data**.
* This situation is **more likely to happen if you have a large number of shards**.
* To solve this problem, **increase the write capacity assigned to the shard table**.
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