The StaleEpochInfo is an ErrorExtraInfo that contains the following fields:

• Namespace
• Received ShardVersion
• Wanted ShardVersion

However, most of the time that this error is thrown, the received and wanted ShardVersions are not entirely known. Instead, we just know either the collection epoch or its timestamp.

In these cases, we just threw a StaleEpoch error without the extra info.

However, in SERVER-109616 we started throwing all the StaleEpoch errors with the StaleEpochInfo to make sure the namespace is propagated to the router so that the collection routing cache can be refreshed.

To achieve that, we set the received and wanted ShardVersions to their default values, which could be confusing.