CBDH Consensus & Transaction Validation Flashcards

What is MVCC (Multi-Version Concurrency Control) in the context of Hyperledger Fabric?

Answer: A conflict detection mechanism that invalidates transactions whose read data changed since simulation

Fabric uses MVCC to detect phantom reads by comparing the read-set key versions from endorsement time against the committed world state at validation time.

In Hyperledger Fabric, what is the 'read set' in a transaction's read-write set?

Answer: The set of keys and their versions read during chaincode simulation

The read set captures each key accessed via GetState along with its version (block number + transaction index) at simulation time, used later for MVCC conflict detection.

What does 'phantom read' protection in Hyperledger Fabric ensure?

Answer: A transaction is invalidated if the range query result would differ at commit time versus simulation time

Phantom read protection invalidates transactions where a range query's result set would be different at commit time due to intervening writes, maintaining serializability.

Which ordering service consensus mode in Fabric requires an external Apache Kafka and ZooKeeper cluster?

Answer: Kafka-based ordering

The Kafka-based ordering service relies on external Kafka brokers and ZooKeeper for crash fault tolerant ordering, though it has been deprecated in favor of Raft.

What is the 'Solo' ordering service in Hyperledger Fabric primarily used for?

Answer: Development and testing environments only

The Solo orderer runs as a single process with no fault tolerance and is only suitable for development and testing, not production.

In a Raft ordering service, what role does the 'leader' node play?

Answer: Receives client transactions and replicates them to follower orderers before cutting blocks

The Raft leader is the single orderer that receives all transactions, appends them to its log, replicates to followers, and cuts blocks once consensus is reached.