45 lines
1.8 KiB
Go
45 lines
1.8 KiB
Go
/*
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Package mpt implements MPT (Merkle-Patricia Trie).
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An MPT stores key-value pairs and is a trie over 16-symbol alphabet. https://en.wikipedia.org/wiki/Trie
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A trie is a tree where values are stored in leafs and keys are paths from the root to the leaf node.
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An MPT consists of 4 types of nodes:
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- Leaf node only contains a value.
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- Extension node contains both a key and a value.
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- Branch node contains 2 or more children.
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- Hash node is a compressed node and only contains the actual node's hash.
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The actual node must be retrieved from the 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 a zero-length key
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- Extension node cannot have another Extension node in its next field
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Thanks 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 in.
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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 quite beneficial:
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When we perform get/put/delete on a specific path, every Hash node which was retrieved from the storage is
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replaced by its uncompressed form, so that subsequent hits of this don't need to access the storage.
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*/
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package mpt
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