@ -790,7 +790,7 @@ In <<fork2>>, we see two miners (Node X and Node Y) who mine two different block
.Visualization of a blockchain fork event: two blocks found simultaneously
image::images/mbc2_1003.png["Visualization of a blockchain fork event: two blocks found simultaneously"]
Let's assume, for example, that a miner Node X finds a Proof-of-Work solution for a block "triangle" that extends the blockchain, building on top of the parent block "star." Almost simultaneously, the miner Node Y who was also extending the chain from block "star" finds a solution for block "upside-down triangle," his candidate block. Now, there are two possible blocks; one we call "triangle," originating in Node X; and one we call "upside-down triangle," originating in Node Y. Both blocks are valid, both blocks contain a valid solution to the Proof-of-Work, and both blocks extend the same parent (block "star"). Both blocks likely contain most of the same transactions, with only perhaps a few differences in the order of transactions.
Let's assume, for example, that the miner Node X finds a Proof-of-Work solution for a block "triangle" that extends the blockchain, building on top of the parent block "star." Almost simultaneously, the miner Node Y who was also extending the chain from block "star" finds a solution for block "upside-down triangle," his candidate block. Now, there are two possible blocks; one we call "triangle," originating in Node X; and one we call "upside-down triangle," originating in Node Y. Both blocks were successfully mined, both blocks are valid (contain a valid solution to the Proof-of-Work), and both blocks extend the same parent (block "star"). Both blocks likely contain most of the same transactions, with only perhaps a few differences in the order of transactions.
As the two blocks propagate, some nodes receive block "triangle" first and some receive block "upside-down triangle" first. As shown in <<fork3>>, the network splits into two different perspectives of the blockchain; one side topped with the triangle block, the other with the upside-down-triangle block.
@ -799,9 +799,9 @@ As the two blocks propagate, some nodes receive block "triangle" first and some
.Visualization of a blockchain fork event: two blocks propagate, splitting the network
image::images/mbc2_1004.png["Visualization of a blockchain fork event: two blocks propagate, splitting the network"]
In the diagram, a randomly chosen "Node X" received the triangle block first and extended the star chain with it. Node X selected the chain with "triangle" block as the main chain. Later, Node X also received the "upside-down triangle" block. Since it was received second, it is assumed to have "lost" the race. Yet, the "upside-down triangle" block is not discarded. It is linked to the "star" block parent and forms a secondary chain. While Node X assumes it has correctly selected the winning chain, it keeps the "losing" chain so that it has the information needed to reconverge if the "losing" chain ends up "winning."
In <<fork3>>, the miner Node X mined (created) the triangle block and extended the star chain with it. Therefore, Node X initially considers the chain with "triangle" block as the main chain. Later, Node X also received the "upside-down triangle" block that was mined by Node Y. Since it was received second, it is assumed to have "lost" the race. Yet, the "upside-down triangle" block is not discarded. It is linked to the "star" block parent and forms a secondary chain. While Node X assumes its main chain is the winning chain, it keeps the "losing" chain so that it has the information needed to reconverge if the "losing" chain ends up "winning."
On the other side of the network, Node Y constructs a blockchain based on its own perspective of the sequence of events. It received "upside-down triangle" first and elected that chain as the "winner." When it later received "triangle" block, it connected it to the "star" block parent as a secondary chain.
On the other side of the network, the miner Node Y constructs a blockchain based on its own perspective of the sequence of events. The miner Node Y mined (created) the "upside-down triangle" and initially considers that chain as the main chain (the "winner" chain). When it later received the "triangle" block that was mined by Node X, it connected it to the "star" block parent as a secondary chain.
Neither side is "correct," or "incorrect." Both are valid perspectives of the blockchain. Only in hindsight will one prevail, based on how these two competing chains are extended by additional work.
@ -809,10 +809,9 @@ Mining nodes whose perspective resembles Node X will immediately begin mining a
Any mining node whose perspective resembles Node Y will start building a candidate block with "upside-down triangle" as its parent, extending the chain that they believe is the main chain. And so, the race begins again.
Forks are almost always resolved within one block. While part of the network's hashing power is dedicated to building on top of "triangle" as the parent, another part of the hashing power is focused on building on top of "upside-down triangle." Even if the hashing power is almost evenly split, it is likely that one set of miners will find a solution and propagate it before the other set of miners have found any solutions. Let's say, for example, that the miners building on top of "triangle" find a new block "rhombus" that extends the chain (e.g., star-triangle-rhombus). They immediately propagate this new block and the entire network sees it as a valid solution as shown in <<fork4>>.
Forks are almost always resolved within one block time (10 minutes on average). While part of the network's hashing power is dedicated to building on top of "triangle" as the parent, another part of the hashing power is focused on building on top of "upside-down triangle." Even if the hashing power is almost evenly split, it is likely that one set of miners will find a solution and propagate it before the other set of miners have found any solutions. Let's say, for example, that the miners building on top of "triangle" find a new block "rhombus" that extends the chain (e.g., star-triangle-rhombus). They immediately propagate this new block and the entire network sees it as a valid solution as shown in <<fork4>>.
All nodes that had chosen "triangle" as the winner in the previous round will simply extend the chain one more block. The nodes that chose "upside-down triangle" as the winner, however, will now see two chains: star-triangle-rhombus and star-upside-down-triangle. The chain star-triangle-rhombus is now longer (more cumulative work) than the other chain. As a result, those nodes will set the chain star-triangle-rhombus as the main chain and change the star-upside-down-triangle chain to a secondary chain, as shown in <<fork5>>. This is a chain reconvergence, because those nodes are forced to revise their view of the blockchain to incorporate the new evidence of a longer chain. Any miners working on extending the chain star-upside-down-triangle will now stop that work because their candidate block is now considered a stale block, as its parent "upside-down-triangle" is no longer on the longest chain. The transactions within "upside-down-triangle" that are not within "triangle" are re-inserted in the mempool for inclusion in the next block to become a part of the main chain. The entire network reconverges on a single blockchain star-triangle-rhombus, with "rhombus" as the last block in the chain. All miners immediately start working on candidate blocks that reference "rhombus" as their parent to extend the star-triangle-rhombus chain.
All nodes that had chosen "triangle" as the winner in the previous round will simply extend the chain one more block. The nodes that chose "upside-down triangle" as the winner, however, will now see two chains: star-triangle-rhombus and star-upside-down-triangle. The chain star-triangle-rhombus is now longer (more cumulative work) than the other chain. As a result, those nodes will set the chain star-triangle-rhombus as the main chain and change the star-upside-down-triangle chain to a secondary chain, as shown in <<fork5>>. This is a chain reconvergence, because those nodes are forced to revise their view of the blockchain to incorporate the new evidence of a longer chain. Any miners working on extending the chain star-upside-down-triangle will now stop that work because their candidate block is now considered a stale block, as its parent "upside-down-triangle" is no longer on the longest chain. Since the upside-down-triangle block is now obsolete, the miner Node Y (which mined this block) will not be able to spend the mining reward for this block, even though this block was valid and was successfully mined. The transactions within "upside-down-triangle" that are not within "triangle" are re-inserted in the mempool for inclusion in the next block to become a part of the main chain. The entire network reconverges on a single blockchain star-triangle-rhombus, with "rhombus" as the last block in the chain. All miners immediately start working on candidate blocks that reference "rhombus" as their parent to extend the star-triangle-rhombus chain.
rating89us
3 years ago
committed by
