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CH12: s/main blockchain/best blockchain/

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David A. Harding 2023-05-25 05:05:55 -10:00
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@ -1450,21 +1450,21 @@ selection of the chain with the most Proof-of-Work. Once a node has
validated a new block, it will then attempt to assemble a chain by validated a new block, it will then attempt to assemble a chain by
connecting the block to the existing blockchain. connecting the block to the existing blockchain.
Nodes maintain three sets of blocks: those connected to the main Nodes maintain three sets of blocks: those connected to the best
blockchain, those that form branches off the main blockchain (secondary blockchain, those that form branches off the best blockchain (stale
chains), and finally, blocks that do not have a known parent in the blocks), and finally, blocks that do not have a known parent in the
known chains (orphans). Invalid blocks are rejected as soon as any one known chains (orphans). Invalid blocks are rejected as soon as any one
of the validation criteria fails and are therefore not included in any of the validation criteria fails and are therefore not included in any
chain. chain.
The "main chain" at any time is whichever _valid_ chain of blocks has The "best blockchain" at any time is whichever _valid_ chain of blocks has
the most cumulative Proof-of-Work associated with it. Under most the most cumulative Proof-of-Work associated with it. Under most
circumstances this is also the chain with the most blocks in it, unless circumstances this is also the chain with the most blocks in it, unless
there are two equal-length chains and one has more Proof-of-Work. The there are two equal-length chains and one has more Proof-of-Work. The
main chain will also have branches with blocks that are "siblings" to best chain will also have branches with blocks that are "siblings" to
the blocks on the main chain. These blocks are valid but not part of the the blocks on the best chain. These blocks are valid but not part of the
main chain. They are kept for future reference, in case one of those best chain. They are kept for future reference, in case one of those
chains is extended to exceed the main chain in work. In the next section chains is extended to exceed the best chain in work. In the next section
(<<forks>>), we will see how secondary chains occur as a result of an (<<forks>>), we will see how secondary chains occur as a result of an
almost simultaneous mining of blocks at the same height. almost simultaneous mining of blocks at the same height.
@ -1472,20 +1472,20 @@ When a new block is received, a node will try to slot it into the
existing blockchain. The node will look at the block's "previous block existing blockchain. The node will look at the block's "previous block
hash" field, which is the reference to the block's parent. Then, the hash" field, which is the reference to the block's parent. Then, the
node will attempt to find that parent in the existing blockchain. Most node will attempt to find that parent in the existing blockchain. Most
of the time, the parent will be the "tip" of the main chain, meaning of the time, the parent will be the "tip" of the best chain, meaning
this new block extends the main chain. For example, the new block this new block extends the best chain. For example, the new block
277,316 has a reference to the hash of its parent block 277,315. Most 277,316 has a reference to the hash of its parent block 277,315. Most
nodes that receive 277,316 will already have block 277,315 as the tip of nodes that receive 277,316 will already have block 277,315 as the tip of
their main chain and will therefore link the new block and extend that their best chain and will therefore link the new block and extend that
chain. chain.
Sometimes, as we will see in <<forks>>, the new block extends a chain Sometimes, as we will see in <<forks>>, the new block extends a chain
that is not the main chain. In that case, the node will attach the new that is not the best chain. In that case, the node will attach the new
block to the secondary chain it extends and then compare the work of the block to the secondary chain it extends and then compare the work of the
secondary chain to the main chain. If the secondary chain has more secondary chain to the best chain. If the secondary chain has more
cumulative work than the main chain, the node will _reconverge_ on the cumulative work than the best chain, the node will _reconverge_ on the
secondary chain, meaning it will select the secondary chain as its new secondary chain, meaning it will select the secondary chain as its new
main chain, making the old main chain a secondary chain. If the node is best chain, making the old best chain a secondary chain. If the node is
a miner, it will now construct a block extending this new, longer, a miner, it will now construct a block extending this new, longer,
chain. chain.
@ -1548,12 +1548,12 @@ Each node has its own perspective of the global blockchain. As each node
receives blocks from its neighbors, it updates its own copy of the receives blocks from its neighbors, it updates its own copy of the
blockchain, selecting the greatest-cumulative-work chain. For blockchain, selecting the greatest-cumulative-work chain. For
illustration purposes, each node contains a shape that represents the illustration purposes, each node contains a shape that represents the
block that it believes is currently the tip of the main chain. So, if block that it believes is currently the tip of the best chain. So, if
you see a star shape in the node, that means that the star block is the you see a star shape in the node, that means that the star block is the
tip of the main chain, as far as that node is concerned. tip of the best chain, as far as that node is concerned.
In the first diagram (<<fork1>>), the network has a unified perspective In the first diagram (<<fork1>>), the network has a unified perspective
of the blockchain, with the star block as the tip of the main chain. of the blockchain, with the star block as the tip of the best chain.
[[fork1]] [[fork1]]
[role="smallereighty"] [role="smallereighty"]
@ -1611,7 +1611,7 @@ image::images/mbc2_1004.png["Visualization of a blockchain fork event: two block
In the diagram, a randomly chosen "Node X" received the triangle block 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 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 with "triangle" block as the best chain. Later, Node X also received the
"upside-down triangle" block. Since it was received second, it is "upside-down triangle" block. Since it was received second, it is
assumed to have "lost" the race. Yet, the "upside-down triangle" block 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 is not discarded. It is linked to the "star" block parent and forms a
@ -1634,11 +1634,11 @@ Mining nodes whose perspective resembles Node X will immediately begin
mining a candidate block that extends the chain with "triangle" as its mining a candidate block that extends the chain with "triangle" as its
tip. By linking "triangle" as the parent of their candidate block, they tip. By linking "triangle" as the parent of their candidate block, they
are voting with their hashing power. Their vote supports the chain that are voting with their hashing power. Their vote supports the chain that
they have elected as the main chain. they have elected as the best chain.
Any mining node whose perspective resembles Node Y will start building a Any mining node whose perspective resembles Node Y will start building a
candidate node with "upside-down triangle" as its parent, extending the candidate node with "upside-down triangle" as its parent, extending the
chain that they believe is the main chain. And so, the race begins chain that they believe is the best chain. And so, the race begins
again. again.
Forks are almost always resolved within one block. While part of the Forks are almost always resolved within one block. While part of the
@ -1658,7 +1658,7 @@ will simply extend the chain one more block. The nodes that chose
star-triangle-rhombus and star-upside-down-triangle. The chain star-triangle-rhombus and star-upside-down-triangle. The chain
star-triangle-rhombus is now longer (more cumulative work) than the star-triangle-rhombus is now longer (more cumulative work) than the
other chain. As a result, those nodes will set the chain other chain. As a result, those nodes will set the chain
star-triangle-rhombus as the main chain and change the star-triangle-rhombus as the best chain and change the
star-upside-down-triangle chain to a secondary chain, as shown in star-upside-down-triangle chain to a secondary chain, as shown in
<<fork5>>. This is a chain reconvergence, because those nodes are forced <<fork5>>. This is a chain reconvergence, because those nodes are forced
to revise their view of the blockchain to incorporate the new evidence to revise their view of the blockchain to incorporate the new evidence
@ -1667,7 +1667,7 @@ star-upside-down-triangle will now stop that work because their
candidate block is an "orphan," as its parent "upside-down-triangle" is candidate block is an "orphan," as its parent "upside-down-triangle" is
no longer on the longest chain. The transactions within no longer on the longest chain. The transactions within
"upside-down-triangle" that are not within "triangle" are re-inserted in "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 the mempool for inclusion in the next block to become a part of the best
chain. The entire network reconverges on a single blockchain chain. The entire network reconverges on a single blockchain
star-triangle-rhombus, with "rhombus" as the last block in the chain. star-triangle-rhombus, with "rhombus" as the last block in the chain.
All miners immediately start working on candidate blocks that reference All miners immediately start working on candidate blocks that reference