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Simple key-value pairs - LevelDB is the default and is particularly appropriate when ledger states are simple key-value pairs. A LevelDB database is closely co-located with a network node – it is embedded within the same operating system process. CouchDB is a particularly appropriate choice when ledger states are structured as JSON documents because CouchDB supports the rich queries and update of richer data types often found in business transactions. Implementation-wise, CouchDB runs in a separate operating system process, but there is still a 1:1 relation between a network node and a CouchDB instance. All of this is invisible to chaincode.

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Peer nodes commits Transaction & keeps the data in sync across the ledger. They are nodes that maintain the state and copy of a shared ledger. Peers are authenticated by certificates issued by MSP. In Hyperledger Fabric, there are three types of peer nodes depending upon the assigned roles.

Getting started- Writing chaincode you will want to make sure that you have the Go programming language installed and correctly configured. Make sure that a directory is created for your chaincode application as a child

The Infrastructure Module includes the following four modules: Technical, Legal, Marketing, and Organizational.

Client Node: That initiates the transaction 2. Peer Nodes: Commits Transaction & keeps the data in sync across the ledger 3. Ordered: They are the communication backbones and responsible for the distribution of the transactions

Code deploying transaction Code deploying transaction submits, updates or terminates a chaincode. The validating nodes protects the authenticity and integrity of the code and its executing environment. Code invoking transaction Code invoking transaction is an API call to a chaincode function. It is similar to how a URI invokes a servlet in JEE. The displayed function is called upon the instantiation of the chaincode. Each chaincode maintains its own state and a function call is made to trigger chaincode state changes.

When the Init, Invoke or Query function of a chaincode is called, the fabric passes the stub *shim.ChaincodeStub parameter. This stub can be used to call APIs to access to the ledger services, transaction context, or to invoke other chaincodes.

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Hyperledger Fabric includes the REST and JSON RPC APIs, events, and an SDK for applications to communicate with the network.

A CouchDB database is closely co-located with a network node and it is embedded within the same operating system process.

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Chaincode has an endorsement policy which specifies the set of peers on a channel that must execute chaincode and endorse the execution results in order for the transaction to be considered valid.

Peer-to-Peer essentially uses data sharing, hosting hardware owned by many not few, fault tolerant, secure, lower performance. It’s common way to share files—a good example was Napster. Peer-to-peer (P2P) file sharing is the distribution of digital media such as software, videos, music, and images through an informal network in order to upload and download files. Typically, P2P software enables users to select which files to share. These files are indexed on a central server, making them available for other users to find and download.

Gossip Protocol The gossip data dissemination protocol performs three functions Manages peer discovery and channel membership Disseminates ledger data across all peers on the channel Syncs ledger state across all peers on the channel.

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Invoke is called to update or query the ledger in a proposal transaction. Init is called during Instantiate transaction after the chaincode container has been established for the first time, allowing the chaincode to initialize its internal data. Invoke is called to update or query the ledger in a proposal transaction. Updated state variables are not committed to the ledger until the transaction is committed.

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