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region_tree.go
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region_tree.go
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// Copyright 2016 PingCAP, Inc.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package core
import (
"bytes"
"math/rand"
"time"
"github.com/pingcap/kvproto/pkg/metapb"
"github.com/pingcap/log"
"github.com/pingcap/pd/v4/pkg/btree"
"go.uber.org/zap"
)
var _ btree.Item = ®ionItem{}
type regionItem struct {
region *RegionInfo
}
// Less returns true if the region start key is less than the other.
func (r *regionItem) Less(other btree.Item) bool {
left := r.region.GetStartKey()
right := other.(*regionItem).region.GetStartKey()
return bytes.Compare(left, right) < 0
}
func (r *regionItem) Contains(key []byte) bool {
start, end := r.region.GetStartKey(), r.region.GetEndKey()
return bytes.Compare(key, start) >= 0 && (len(end) == 0 || bytes.Compare(key, end) < 0)
}
const (
defaultBTreeDegree = 64
)
type regionTree struct {
tree *btree.BTree
}
func newRegionTree() *regionTree {
return ®ionTree{
tree: btree.New(defaultBTreeDegree),
}
}
func (t *regionTree) length() int {
return t.tree.Len()
}
// getOverlaps gets the regions which are overlapped with the specified region range.
func (t *regionTree) getOverlaps(region *RegionInfo) []*RegionInfo {
item := ®ionItem{region: region}
// note that find() gets the last item that is less or equal than the region.
// in the case: |_______a_______|_____b_____|___c___|
// new region is |______d______|
// find() will return regionItem of region_a
// and both startKey of region_a and region_b are less than endKey of region_d,
// thus they are regarded as overlapped regions.
result := t.find(region)
if result == nil {
result = item
}
var overlaps []*RegionInfo
t.tree.AscendGreaterOrEqual(result, func(i btree.Item) bool {
over := i.(*regionItem)
if len(region.GetEndKey()) > 0 && bytes.Compare(region.GetEndKey(), over.region.GetStartKey()) <= 0 {
return false
}
overlaps = append(overlaps, over.region)
return true
})
return overlaps
}
// update updates the tree with the region.
// It finds and deletes all the overlapped regions first, and then
// insert the region.
func (t *regionTree) update(region *RegionInfo) []*RegionInfo {
overlaps := t.getOverlaps(region)
for _, item := range overlaps {
log.Debug("overlapping region",
zap.Uint64("region-id", item.GetID()),
zap.Stringer("delete-region", RegionToHexMeta(item.GetMeta())),
zap.Stringer("update-region", RegionToHexMeta(region.GetMeta())))
t.tree.Delete(®ionItem{item})
}
t.tree.ReplaceOrInsert(®ionItem{region: region})
return overlaps
}
// remove removes a region if the region is in the tree.
// It will do nothing if it cannot find the region or the found region
// is not the same with the region.
func (t *regionTree) remove(region *RegionInfo) btree.Item {
if t.length() == 0 {
return nil
}
result := t.find(region)
if result == nil || result.region.GetID() != region.GetID() {
return nil
}
return t.tree.Delete(result)
}
// search returns a region that contains the key.
func (t *regionTree) search(regionKey []byte) *RegionInfo {
region := &RegionInfo{meta: &metapb.Region{StartKey: regionKey}}
result := t.find(region)
if result == nil {
return nil
}
return result.region
}
// searchPrev returns the previous region of the region where the regionKey is located.
func (t *regionTree) searchPrev(regionKey []byte) *RegionInfo {
curRegion := &RegionInfo{meta: &metapb.Region{StartKey: regionKey}}
curRegionItem := t.find(curRegion)
if curRegionItem == nil {
return nil
}
prevRegionItem, _ := t.getAdjacentRegions(curRegionItem.region)
if prevRegionItem == nil {
return nil
}
if !bytes.Equal(prevRegionItem.region.GetEndKey(), curRegionItem.region.GetStartKey()) {
return nil
}
return prevRegionItem.region
}
// find is a helper function to find an item that contains the regions start
// key.
func (t *regionTree) find(region *RegionInfo) *regionItem {
item := ®ionItem{region: region}
var result *regionItem
t.tree.DescendLessOrEqual(item, func(i btree.Item) bool {
result = i.(*regionItem)
return false
})
if result == nil || !result.Contains(region.GetStartKey()) {
return nil
}
return result
}
// scanRage scans from the first region containing or behind the start key
// until f return false
func (t *regionTree) scanRange(startKey []byte, f func(*RegionInfo) bool) {
region := &RegionInfo{meta: &metapb.Region{StartKey: startKey}}
// find if there is a region with key range [s, d), s < startKey < d
startItem := t.find(region)
if startItem == nil {
startItem = ®ionItem{region: &RegionInfo{meta: &metapb.Region{StartKey: startKey}}}
}
t.tree.AscendGreaterOrEqual(startItem, func(item btree.Item) bool {
return f(item.(*regionItem).region)
})
}
func (t *regionTree) getAdjacentRegions(region *RegionInfo) (*regionItem, *regionItem) {
item := ®ionItem{region: &RegionInfo{meta: &metapb.Region{StartKey: region.GetStartKey()}}}
var prev, next *regionItem
t.tree.AscendGreaterOrEqual(item, func(i btree.Item) bool {
if bytes.Equal(item.region.GetStartKey(), i.(*regionItem).region.GetStartKey()) {
return true
}
next = i.(*regionItem)
return false
})
t.tree.DescendLessOrEqual(item, func(i btree.Item) bool {
if bytes.Equal(item.region.GetStartKey(), i.(*regionItem).region.GetStartKey()) {
return true
}
prev = i.(*regionItem)
return false
})
return prev, next
}
// RandomRegion is used to get a random region within ranges.
func (t *regionTree) RandomRegion(ranges []KeyRange) *RegionInfo {
if t.length() == 0 {
return nil
}
if len(ranges) == 0 {
ranges = []KeyRange{NewKeyRange("", "")}
}
for _, i := range rand.Perm(len(ranges)) {
var endIndex int
startKey, endKey := ranges[i].StartKey, ranges[i].EndKey
startRegion, startIndex := t.tree.GetWithIndex(®ionItem{region: &RegionInfo{meta: &metapb.Region{StartKey: startKey}}})
if len(endKey) != 0 {
_, endIndex = t.tree.GetWithIndex(®ionItem{region: &RegionInfo{meta: &metapb.Region{StartKey: endKey}}})
} else {
endIndex = t.tree.Len()
}
// Consider that the item in the tree may not be continuous,
// we need to check if the previous item contains the key.
if startIndex != 0 && startRegion == nil && t.tree.GetAt(startIndex-1).(*regionItem).Contains(startKey) {
startIndex--
}
if endIndex <= startIndex {
if len(endKey) > 0 && bytes.Compare(startKey, endKey) > 0 {
log.Error("wrong range keys",
zap.String("start-key", string(HexRegionKey(startKey))),
zap.String("end-key", string(HexRegionKey(endKey))))
}
continue
}
index := rand.Intn(endIndex-startIndex) + startIndex
region := t.tree.GetAt(index).(*regionItem).region
if isInvolved(region, startKey, endKey) {
return region
}
}
return nil
}
func init() {
rand.Seed(time.Now().UnixNano())
}