frostfs-node/pkg/local_object_storage/pilorama/inmemory.go
Evgenii Stratonikov cf73feb3f8 [#1324] local_object_storage: Implement tree service backend
In this commit we implement algorithm for CRDT trees from
https://martin.klepmann.com/papers/move-op.pdf

Each tree is identified by the ID of a container it belongs to
and the tree name itself. Essentially, it is a sequence of operations
which should be applied in chronological order to get a usual tree
representation.

There are 2 backends for now: bbolt database and in-memory.
In-memory backend is here for debugging and will eventually act
as a memory-cache for the on-disk database.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>
2022-07-08 12:47:40 +03:00

235 lines
4.9 KiB
Go

package pilorama
// nodeInfo couples parent and metadata.
type nodeInfo struct {
Parent Node
Meta Meta
Timestamp Timestamp
}
// state represents state being replicated.
type state struct {
operations []LogMove
tree
}
// newState constructs new empty tree.
func newState() *state {
return &state{
tree: *newTree(),
}
}
// undo un-does op and changes s in-place.
func (s *state) undo(op *LogMove) {
children := s.tree.childMap[op.Parent]
for i := range children {
if children[i] == op.Child {
if len(children) > 1 {
s.tree.childMap[op.Parent] = append(children[:i], children[i+1:]...)
} else {
delete(s.tree.childMap, op.Parent)
}
break
}
}
if op.HasOld {
s.tree.infoMap[op.Child] = op.Old
oldChildren := s.tree.childMap[op.Old.Parent]
for i := range oldChildren {
if oldChildren[i] == op.Child {
return
}
}
s.tree.childMap[op.Old.Parent] = append(oldChildren, op.Child)
} else {
delete(s.tree.infoMap, op.Child)
}
}
// Apply puts op in log at a proper position, re-applies all subsequent operations
// from log and changes s in-place.
func (s *state) Apply(op *Move) error {
var index int
for index = len(s.operations); index > 0; index-- {
if s.operations[index-1].Time <= op.Time {
break
}
}
if index == len(s.operations) {
s.operations = append(s.operations, s.do(op))
return nil
}
s.operations = append(s.operations[:index+1], s.operations[index:]...)
for i := len(s.operations) - 1; i > index; i-- {
s.undo(&s.operations[i])
}
s.operations[index] = s.do(op)
for i := index + 1; i < len(s.operations); i++ {
s.operations[i] = s.do(&s.operations[i].Move)
}
return nil
}
// do performs a single move operation on a tree.
func (s *state) do(op *Move) LogMove {
lm := LogMove{
Move: Move{
Parent: op.Parent,
Meta: op.Meta,
Child: op.Child,
},
}
_, parentInTree := s.tree.infoMap[op.Parent]
shouldPut := !s.tree.isAncestor(op.Child, op.Parent) &&
!(op.Parent != 0 && op.Parent != TrashID && !parentInTree)
shouldRemove := op.Parent == TrashID
p, ok := s.tree.infoMap[op.Child]
if ok {
lm.HasOld = true
lm.Old = p
}
if !shouldPut {
return lm
}
if shouldRemove {
if ok {
s.removeChild(op.Child, p.Parent)
}
delete(s.tree.infoMap, op.Child)
return lm
}
if !ok {
p.Timestamp = op.Time
} else {
s.removeChild(op.Child, p.Parent)
}
p.Meta = op.Meta
p.Parent = op.Parent
s.tree.infoMap[op.Child] = p
s.tree.childMap[op.Parent] = append(s.tree.childMap[op.Parent], op.Child)
return lm
}
func (s *state) removeChild(child, parent Node) {
oldChildren := s.tree.childMap[parent]
for i := range oldChildren {
if oldChildren[i] == child {
s.tree.childMap[parent] = append(oldChildren[:i], oldChildren[i+1:]...)
break
}
}
}
func (s *state) timestamp() Timestamp {
if len(s.operations) == 0 {
return 0
}
return s.operations[len(s.operations)-1].Time + 1
}
func (s *state) findSpareID() Node {
id := uint64(1)
for _, ok := s.infoMap[id]; ok; _, ok = s.infoMap[id] {
id++
}
return id
}
// tree is a mapping from the child nodes to their parent and metadata.
type tree struct {
infoMap map[Node]nodeInfo
childMap map[Node][]Node
}
func newTree() *tree {
return &tree{
childMap: make(map[Node][]Node),
infoMap: make(map[Node]nodeInfo),
}
}
// isAncestor returns true if parent is an ancestor of a child.
// For convenience, also return true if parent == child.
func (t tree) isAncestor(parent, child Node) bool {
for c := child; c != parent; {
p, ok := t.infoMap[c]
if !ok {
return false
}
c = p.Parent
}
return true
}
// getPathPrefix descends by path constructed from values of attr until
// there is no node corresponding to a path element. Returns the amount of nodes
// processed and ID of the last node.
func (t tree) getPathPrefix(attr string, path []string) (int, Node) {
var curNode Node
loop:
for i := range path {
children := t.childMap[curNode]
for j := range children {
f := t.infoMap[children[j]].Meta.GetAttr(attr)
if string(f) == path[i] {
curNode = children[j]
continue loop
}
}
return i, curNode
}
return len(path), curNode
}
// get returns list of nodes which have the specified path from root
// descending by values of attr from meta.
func (t tree) get(attr string, path []string, latest bool) []Node {
if len(path) == 0 {
return nil
}
i, curNode := t.getPathPrefix(attr, path[:len(path)-1])
if i < len(path)-1 {
return nil
}
var nodes []Node
var lastTs Timestamp
children := t.childMap[curNode]
for i := range children {
info := t.infoMap[children[i]]
fileName := string(info.Meta.GetAttr(attr))
if fileName == path[len(path)-1] {
if latest {
if info.Timestamp >= lastTs {
nodes = append(nodes[:0], children[i])
}
} else {
nodes = append(nodes, children[i])
}
}
}
return nodes
}
// getMeta returns meta information of node n.
func (t tree) getMeta(n Node) Meta {
return t.infoMap[n].Meta
}