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package bolt
import (
"bytes"
"unsafe"
)
// branch represents a temporary in-memory branch page.
type branch struct {
parent *branch
items branchItems
}
// size returns the size of the branch after serialization.
func (b *branch) size() int {
var size int = pageHeaderSize
for _, item := range b.items {
size += bnodeSize + len(item.key)
}
return size
}
// put adds a new node or replaces an existing node.
func (b *branch) put(id pgid, newid pgid, key []byte, replace bool) {
var index int
for ; index < len(b.items); index++ {
if b.items[index].pgid == id {
break
}
}
if !replace {
index++
b.items = append(b.items, branchItem{})
if index < len(b.items) {
copy(b.items[index+1:], b.items[index:])
}
}
b.items[index].pgid = newid
b.items[index].key = key
}
// read initializes the item data from an on-disk page.
func (b *branch) read(page *page) {
ncount := int(page.count)
b.items = make(branchItems, ncount)
bnodes := (*[maxNodesPerPage]bnode)(unsafe.Pointer(&page.ptr))
for i := 0; i < ncount; i++ {
bnode := &bnodes[i]
item := &b.items[i]
item.pgid = bnode.pgid
item.key = bnode.key()
}
}
// write writes the items onto a branch page.
func (b *branch) write(p *page) {
// Initialize page.
p.flags |= p_branch
p.count = uint16(len(b.items))
// Loop over each item and write it to the page.
bnodes := (*[maxNodesPerPage]bnode)(unsafe.Pointer(&p.ptr))
buf := (*[maxAllocSize]byte)(unsafe.Pointer(&p.ptr))[lnodeSize*len(b.items):]
for index, item := range b.items {
// Write node.
bnode := &bnodes[index]
bnode.pgid = item.pgid
bnode.pos = uint32(uintptr(unsafe.Pointer(&buf[0])) - uintptr(unsafe.Pointer(bnode)))
bnode.ksize = uint32(len(item.key))
// Write key to the end of the page.
copy(buf[0:], item.key)
buf = buf[len(item.key):]
}
}
// split divides up the noes in the branch into appropriately sized groups.
func (b *branch) split(pageSize int) []*branch {
// Ignore the split if the page doesn't have at least enough nodes for
// multiple pages or if the data can fit on a single page.
if len(b.items) <= (minKeysPerPage * 2) || b.size() < pageSize {
return []*branch{b}
}
// Set fill threshold to 50%.
threshold := pageSize / 2
// Otherwise group into smaller pages and target a given fill size.
size := 0
current := &branch{}
branches := make([]*branch, 0)
for index, item := range b.items {
nodeSize := bnodeSize + len(item.key)
if (len(current.items) >= minKeysPerPage && index < len(b.items)-minKeysPerPage && size+nodeSize > threshold) {
size = pageHeaderSize
branches = append(branches, current)
current = &branch{}
}
size += nodeSize
current.items = append(current.items, item)
}
branches = append(branches, current)
return branches
}
type branchItems []branchItem
type branchItem struct {
pgid pgid
key []byte
}
func (s branchItems) Len() int { return len(s) }
func (s branchItems) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
func (s branchItems) Less(i, j int) bool { return bytes.Compare(s[i].key, s[j].key) == -1 }
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