mirror of
https://github.com/nspcc-dev/neo-go.git
synced 2024-12-14 23:07:50 +00:00
46 lines
1.8 KiB
Go
46 lines
1.8 KiB
Go
|
/*
|
||
|
|
Package mpt implements MPT (Merkle-Patricia Tree).
|
||
|
|
|
||
|
|
MPT stores key-value pairs and is a trie over 16-symbol alphabet. https://en.wikipedia.org/wiki/Trie
|
||
|
|
Trie is a tree where values are stored in leafs and keys are paths from root to the leaf node.
|
||
|
|
MPT consists of 4 type of nodes:
|
||
|
|
- Leaf node contains only value.
|
||
|
|
- Extension node contains both key and value.
|
||
|
|
- Branch node contains 2 or more children.
|
||
|
|
- Hash node is a compressed node and contains only actual node's hash.
|
||
|
|
The actual node must be retrieved from 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 zero-length key
|
||
|
|
- Extension node cannot have another Extension node in it's next field
|
||
|
|
|
||
|
|
Thank to these restrictions, there is a single root hash for every set of key-value pairs
|
||
|
|
irregardless of the order they were added/removed with.
|
||
|
|
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 very beneficial:
|
||
|
|
When we perform get/put/delete on a speficic path, every Hash node which was retreived from storage is
|
||
|
|
replaced by its uncompressed form, so that subsequent hits of this not don't use storage.
|
||
|
|
*/
|
||
|
|
package mpt
|