neo-go/pkg/core/mpt/doc.go
Anna Shaleva 916f2293b8 *: apply go 1.19 formatter heuristics
And make manual corrections where needed. See the "Common mistakes
and pitfalls" section of https://tip.golang.org/doc/comment.
2022-08-09 15:37:52 +03:00

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