* A Promise is added via newReadOnlyTransaction. When the parent class completes the primary shard
* lookup and creates the TransactionContext (either success or failure), onTransactionContextCreated is
* called which completes the Promise. A write tx that is created prior to completion will wait on the
* Promise's Future via findPrimaryShard.
*/
* A Promise is added via newReadOnlyTransaction. When the parent class completes the primary shard
* lookup and creates the TransactionContext (either success or failure), onTransactionContextCreated is
* called which completes the Promise. A write tx that is created prior to completion will wait on the
* Promise's Future via findPrimaryShard.
*/