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46 lines
1.8 KiB
Go
46 lines
1.8 KiB
Go
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/*
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Package mpt implements MPT (Merkle-Patricia Tree).
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MPT stores key-value pairs and is a trie over 16-symbol alphabet. https://en.wikipedia.org/wiki/Trie
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Trie is a tree where values are stored in leafs and keys are paths from root to the leaf node.
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MPT consists of 4 type of nodes:
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- Leaf node contains only value.
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- Extension node contains both key and value.
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- Branch node contains 2 or more children.
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- Hash node is a compressed node and contains only actual node's hash.
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The actual node must be retrieved from storage or over the network.
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As an example here is a trie containing 3 pairs:
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- 0x1201 -> val1
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- 0x1203 -> val2
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- 0x1224 -> val3
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- 0x12 -> val4
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ExtensionNode(0x0102), Next
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_______________________|
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BranchNode [0, 1, 2, ...], Last -> Leaf(val4)
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| ExtensionNode [0x04], Next -> Leaf(val3)
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BranchNode [0, 1, 2, 3, ...], Last -> HashNode(nil)
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| Leaf(val2)
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Leaf(val1)
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There are 3 invariants that this implementation has:
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- Branch node cannot have <= 1 children
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- Extension node cannot have zero-length key
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- Extension node cannot have another Extension node in it's next field
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Thank to these restrictions, there is a single root hash for every set of key-value pairs
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irregardless of the order they were added/removed with.
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The actual trie structure can vary because of node -> HashNode compressing.
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There is also one optimization which cost us almost nothing in terms of complexity but is very beneficial:
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When we perform get/put/delete on a speficic path, every Hash node which was retreived from storage is
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replaced by its uncompressed form, so that subsequent hits of this not don't use storage.
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*/
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package mpt
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