The leader can be thought of as a recommendation or proxy for who should mint -- and it is generally true that there is only a single minter -- but we do not rely on the maximum of one concurrent minter for correctness.
During such a transition it's possible that two nodes are both minting for a short period of time. In this scenario there will be a race, the first block that successfully extends the chain will win, and the loser of the race will be ignored. Consider the following example where this might occur, where Raft entries attempting to extend the chain are denoted like:.
Where 0xbeda is the ID of new block, and 0xacaa is the ID of its parent. Here, the initial minter node 1 is partitioned, and node 2 takes over as the minter. Once the partition heals, at the Raft layer node1 will resubmit 0x2c52 , and the resulting serialized log might look as follows:. Due to being serialized after the "winner," the "loser" entry will not extend the chain, because its parent 0xbeda is no longer at the head of the chain when we apply the entry.
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The "winner" extended the same parent 0xbeda earlier and then 0xc extended it further. From Raft's point of view, each log entry is valid, but at the Quorum-Raft level, we choose which entries will be "used," and will actually extend the chain. This chain extension logic is deterministic: the same exact behavior will occur on every single node in the cluster, keeping the blockchain in sync.
Also note how our approach differs from the "longest valid chain" LVC mechanism from vanilla Ethereum. LVC is used to resolve forks in a network that is eventually consistent. Because we use Raft, the state of the blockchain is strongly consistent.
There can not be forks in the Raft setting. Once a block has been added as the new head of the chain, it is done so for the entire cluster, and it is permanent. As a default, we mint blocks no more frequently than every 50ms. When new transactions come in we will mint a new block immediately so latency is low , but we will only mint a block if it's been at least 50ms since the last block so we don't flood raft with blocks. This rate limiting achieves a balance between transaction throughput and latency. One of the ways our approach differs from vanilla Ethereum is that we introduce a new concept of "speculative minting.
It takes some time for a block to flow through Raft consensus and become the head of the chain. If we synchronously waited for a block to become the new head of the chain before creating the new block, any transactions that we receive would take more time to make it into the chain.
In speculative minting we allow the creation of a new block and its proposal to Raft before its parent has made it all the way through Raft and into the blockchain. Since this can happen repeatedly, these blocks which each have a reference to their parent block can form a sort of chain. We call this a "speculative chain. During the course of operation that a speculative chain forms, we keep track of the subset of transactions in the pool that we have already put into blocks in the speculative chain that have not yet made it into the blockchain and whereupon a core.
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Per the presence of "races" as we detail above , it is possible that a block somewhere in the middle of a speculative chain ends up not making into the chain. In this scenario an InvalidRaftOrdering event will occur, and we clean up the state of the speculative chain accordingly. There is currently no limit to the length of these speculative chains, but we plan to add support for this in the future. As a consequence, a minter can currently create arbitrarily many blocks back-to-back in a scenario where Raft stops making progress. It's also at least theoretically possible to use the p2p protocol built-in to Ethereum as a transport for Raft.
In our testing we found the default etcd HTTP transport to be more reliable than the p2p at least as implemented in geth under high load. Quorum listens on port by default for the raft transport, but this is configurable with the --raftport flag.
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Default number of peers is set to be Max number of peers is configurable with the --maxpeers N where N is expected size of the cluster. Currently Raft-based consensus requires that all initial nodes in the cluster are configured to list the others up-front as static peers. These enode ID URIs must include a raftport querystring parameter specifying the raft port for each peer: e. Note that the order of the enodes in the static-nodes. To remove a node from the cluster, attach to a JS console and issue raft.
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For initial nodes in the cluster, this number is the 1-indexed position of the node's enode ID in the static peers list. Once a node has been removed from the cluster, it is permanent; this raft ID can not ever re-connect to the cluster in the future, and the party must re-join the cluster with a new raft ID. To add a node to the cluster, attach to a JS console and issue raft.
This call will allocate and return a raft ID that was not already in use. Answers to frequently asked questions can be found on the main Quorum FAQ page. Skip to content. Permalink Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. Branch: master Find file Copy path. Find file Copy path. Raw Blame History. Both Raft and Ethereum have their own notion of a "node": In Raft, a node in normal operation is either a "leader" or a "follower.
Ethereum Raft minter leader verifier follower The main reasons we co-locate the leader and minter are 1 convenience, in that Raft ensures there is only one leader at a time, and 2 to avoid a network hop from a node minting blocks to the leader, through which all Raft writes must flow. The lifecycle of a transaction Let's follow the lifecycle of a typical transaction: on any node whether minter or verifier : The transaction is submitted via an RPC call to geth.
Using the existing p2p transaction propagation mechanism in Ethereum, the transaction is announced to all peers and, because our cluster is currently configured to use "static nodes," every transaction is sent to all peers in the cluster. Its job is to RLP-encode blocks and propose them to Raft. However, thirst and hunger is not the only danger in the ocean… watch out for the man-eating shark determined to end your voyage!
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