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trie: simplify StackTrie implementation (ethereum#23950)
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Trim the search key from head as it's being pushed deeper into the trie. Previously the search key was never modified but each node kept information how to slice and compare it in keyOffset. Now the keyOffset is not needed as this information is included in the slice of the search key. This way the keyOffset can be removed and key manipulation
simplified.
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@chfast
chfast authored Nov 29, 2021
1 parent c10a0a6 commit 86fe359
Showing 1 changed file with 32 additions and 40 deletions.
72 changes: 32 additions & 40 deletions trie/stacktrie.go
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Original file line number Diff line number Diff line change
Expand Up @@ -54,12 +54,11 @@ func returnToPool(st *StackTrie) {
// in order. Once it determines that a subtree will no longer be inserted
// into, it will hash it and free up the memory it uses.
type StackTrie struct {
nodeType uint8 // node type (as in branch, ext, leaf)
val []byte // value contained by this node if it's a leaf
key []byte // key chunk covered by this (full|ext) node
keyOffset int // offset of the key chunk inside a full key
children [16]*StackTrie // list of children (for fullnodes and exts)
db ethdb.KeyValueWriter // Pointer to the commit db, can be nil
nodeType uint8 // node type (as in branch, ext, leaf)
val []byte // value contained by this node if it's a leaf
key []byte // key chunk covered by this (leaf|ext) node
children [16]*StackTrie // list of children (for branch and exts)
db ethdb.KeyValueWriter // Pointer to the commit db, can be nil
}

// NewStackTrie allocates and initializes an empty trie.
Expand Down Expand Up @@ -90,15 +89,13 @@ func (st *StackTrie) MarshalBinary() (data []byte, err error) {
w = bufio.NewWriter(&b)
)
if err := gob.NewEncoder(w).Encode(struct {
Nodetype uint8
Val []byte
Key []byte
KeyOffset uint8
Nodetype uint8
Val []byte
Key []byte
}{
st.nodeType,
st.val,
st.key,
uint8(st.keyOffset),
}); err != nil {
return nil, err
}
Expand Down Expand Up @@ -126,16 +123,14 @@ func (st *StackTrie) UnmarshalBinary(data []byte) error {

func (st *StackTrie) unmarshalBinary(r io.Reader) error {
var dec struct {
Nodetype uint8
Val []byte
Key []byte
KeyOffset uint8
Nodetype uint8
Val []byte
Key []byte
}
gob.NewDecoder(r).Decode(&dec)
st.nodeType = dec.Nodetype
st.val = dec.Val
st.key = dec.Key
st.keyOffset = int(dec.KeyOffset)

var hasChild = make([]byte, 1)
for i := range st.children {
Expand All @@ -160,20 +155,18 @@ func (st *StackTrie) setDb(db ethdb.KeyValueWriter) {
}
}

func newLeaf(ko int, key, val []byte, db ethdb.KeyValueWriter) *StackTrie {
func newLeaf(key, val []byte, db ethdb.KeyValueWriter) *StackTrie {
st := stackTrieFromPool(db)
st.nodeType = leafNode
st.keyOffset = ko
st.key = append(st.key, key[ko:]...)
st.key = append(st.key, key...)
st.val = val
return st
}

func newExt(ko int, key []byte, child *StackTrie, db ethdb.KeyValueWriter) *StackTrie {
func newExt(key []byte, child *StackTrie, db ethdb.KeyValueWriter) *StackTrie {
st := stackTrieFromPool(db)
st.nodeType = extNode
st.keyOffset = ko
st.key = append(st.key, key[ko:]...)
st.key = append(st.key, key...)
st.children[0] = child
return st
}
Expand Down Expand Up @@ -211,25 +204,26 @@ func (st *StackTrie) Reset() {
st.children[i] = nil
}
st.nodeType = emptyNode
st.keyOffset = 0
}

// Helper function that, given a full key, determines the index
// at which the chunk pointed by st.keyOffset is different from
// the same chunk in the full key.
func (st *StackTrie) getDiffIndex(key []byte) int {
diffindex := 0
for ; diffindex < len(st.key) && st.key[diffindex] == key[st.keyOffset+diffindex]; diffindex++ {
for idx, nibble := range st.key {
if nibble != key[idx] {
return idx
}
}
return diffindex
return len(st.key)
}

// Helper function to that inserts a (key, value) pair into
// the trie.
func (st *StackTrie) insert(key, value []byte) {
switch st.nodeType {
case branchNode: /* Branch */
idx := int(key[st.keyOffset])
idx := int(key[0])
// Unresolve elder siblings
for i := idx - 1; i >= 0; i-- {
if st.children[i] != nil {
Expand All @@ -241,10 +235,10 @@ func (st *StackTrie) insert(key, value []byte) {
}
// Add new child
if st.children[idx] == nil {
st.children[idx] = stackTrieFromPool(st.db)
st.children[idx].keyOffset = st.keyOffset + 1
st.children[idx] = newLeaf(key[1:], value, st.db)
} else {
st.children[idx].insert(key[1:], value)
}
st.children[idx].insert(key, value)
case extNode: /* Ext */
// Compare both key chunks and see where they differ
diffidx := st.getDiffIndex(key)
Expand All @@ -257,7 +251,7 @@ func (st *StackTrie) insert(key, value []byte) {
if diffidx == len(st.key) {
// Ext key and key segment are identical, recurse into
// the child node.
st.children[0].insert(key, value)
st.children[0].insert(key[diffidx:], value)
return
}
// Save the original part. Depending if the break is
Expand All @@ -266,7 +260,7 @@ func (st *StackTrie) insert(key, value []byte) {
// node directly.
var n *StackTrie
if diffidx < len(st.key)-1 {
n = newExt(diffidx+1, st.key, st.children[0], st.db)
n = newExt(st.key[diffidx+1:], st.children[0], st.db)
} else {
// Break on the last byte, no need to insert
// an extension node: reuse the current node
Expand All @@ -288,15 +282,14 @@ func (st *StackTrie) insert(key, value []byte) {
// node.
st.children[0] = stackTrieFromPool(st.db)
st.children[0].nodeType = branchNode
st.children[0].keyOffset = st.keyOffset + diffidx
p = st.children[0]
}
// Create a leaf for the inserted part
o := newLeaf(st.keyOffset+diffidx+1, key, value, st.db)
o := newLeaf(key[diffidx+1:], value, st.db)

// Insert both child leaves where they belong:
origIdx := st.key[diffidx]
newIdx := key[diffidx+st.keyOffset]
newIdx := key[diffidx]
p.children[origIdx] = n
p.children[newIdx] = o
st.key = st.key[:diffidx]
Expand Down Expand Up @@ -330,7 +323,6 @@ func (st *StackTrie) insert(key, value []byte) {
st.nodeType = extNode
st.children[0] = NewStackTrie(st.db)
st.children[0].nodeType = branchNode
st.children[0].keyOffset = st.keyOffset + diffidx
p = st.children[0]
}

Expand All @@ -339,19 +331,19 @@ func (st *StackTrie) insert(key, value []byte) {
// The child leave will be hashed directly in order to
// free up some memory.
origIdx := st.key[diffidx]
p.children[origIdx] = newLeaf(diffidx+1, st.key, st.val, st.db)
p.children[origIdx] = newLeaf(st.key[diffidx+1:], st.val, st.db)
p.children[origIdx].hash()

newIdx := key[diffidx+st.keyOffset]
p.children[newIdx] = newLeaf(p.keyOffset+1, key, value, st.db)
newIdx := key[diffidx]
p.children[newIdx] = newLeaf(key[diffidx+1:], value, st.db)

// Finally, cut off the key part that has been passed
// over to the children.
st.key = st.key[:diffidx]
st.val = nil
case emptyNode: /* Empty */
st.nodeType = leafNode
st.key = key[st.keyOffset:]
st.key = key
st.val = value
case hashedNode:
panic("trying to insert into hash")
Expand Down

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