Linux Foundation HFCP - Hyperledger Fabric Certified Practitioner (HFCP) Exam

In the context of the Fabric Gateway client API, the call that a client application would use to update the ledger state is Submit1. The Submit function combines the actions of endorsing a transaction proposal, submitting the transaction to the ordering service, and waiting for the transaction to be committed to the ledger into a single blocking call. This simplifies the process for the client application, allowing it to update the ledger state with a single line of code. The Evaluate call, on the other hand, is used to query the current state of the ledger without making any updates2. There are no Invoke or Update calls in the Fabric Gateway client API as per the official documentation

Intercommunication in Hyperledger Fabric regarding how smart contracts update the World State database is primarily achieved by calling other smart contracts, both within the same channel and across different channels. This process allows smart contracts, also known as chaincode, to interact and transact across the network, updating the World State as necessary based on business logic defined in the contracts. This capability is crucial for complex business processes that span multiple contracts and possibly multiple channels. Unlike setting endorsement policies or configuring peer-to-peer options, calling other smart contracts directly facilitates dynamic and direct interaction between business processes, enhancing the modularity and efficiency of the network. Cross-channel communication must be carefully managed within the permissions and policies defined in the network to maintain security and integrity​​.

In Hyperledger Fabric, the peer CLI (Command Line Interface) tool is used to update channels or invoke new smart contracts. This utility allows users to perform various administrative tasks on the network, such as updating the ledger, changing endorsement policies, and managing chaincode installations and instantiations .

When using LevelDB as the state database in Hyperledger Fabric, there is no specific schema that the data stored in the ledger needs to adhere to. LevelDB is a key-value store, which does not enforce any schema on the data it holds. This flexibility allows applications to define their own formats and structures for the data they store, which can vary from simple strings and numbers to more complex serialized data structures. This schema-less nature of LevelDB enables developers to implement the data handling that best suits their application's needs without the constraints of a predefined database schema​​.

The gRPC status code "UNAVAILABLE" is commonly expected in scenarios involving transient failures in network communication, such as a disconnection between the client application and the Gateway peer. This status code indicates that the service is currently unavailable, often due to network issues or service downtime, making it suitable for situations where the failure is temporary and the request can be retried. This differs from other codes like "ABORTED" or "DEADLINE EXCEEDED," which represent different types of errors related to the transaction logic or timing issues, respectively. "FAILED PRECONDITION" would be inappropriate for network disconnections as it suggests issues with the request's preconditions, not the network status​​.

In Hyperledger Fabric, when executing queries on the ledger, the difference between simple keys and composite keys is significant. Simple keys consist of a single attribute and are straightforward in their use for querying. In contrast, composite keys are formed by combining multiple attributes into a single key, allowing for more complex queries based on multiple fields. Composite keys enable richer, more flexible query capabilities that can facilitate refined searches and analyses within the ledger. This capability is particularly useful in scenarios where a single attribute is not sufficient to uniquely identify ledger entries or when queries need to filter based on multiple criteria​​.

In Hyperledger Fabric, private data collections are designed to enhance privacy and confidentiality by allowing only specified members of a collection to access the stored data. These members are pre-configured when the private data collection is defined. While the actual data is restricted to these configured members, hash values of the data are distributed and stored on the ledger accessible by all organizations in the channel. This method ensures data confidentiality while still providing a way to verify data integrity across the entire channel, as other organizations can see the hash values but not the actual data itself​​.

In Hyperledger Fabric, the Gateway service manages the transaction submission process on behalf of the client application. This service simplifies the interaction with the network by abstracting the details of transaction construction, endorsement, and submission. The Gateway service assembles the necessary endorsements according to the relevant chaincode endorsement policies and submits the transaction to the ordering service. This role of the Gateway enhances the usability and efficiency of transaction processing, reducing the complexity for client applications by handling these critical steps internally​​.

In Hyperledger Fabric, a unique ID to represent an asset on the ledger is typically generated in the client application before the transaction is submitted to the blockchain. This approach ensures that each asset has a unique identifier, which is crucial for tracking and managing assets throughout their lifecycle on the ledger​​.