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segment_stack.go
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240 lines (201 loc) · 6.03 KB
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// Copyright 2016-Present Couchbase, Inc.
//
// Use of this software is governed by the Business Source License included
// in the file licenses/BSL-Couchbase.txt. As of the Change Date specified
// in that file, in accordance with the Business Source License, use of this
// software will be governed by the Apache License, Version 2.0, included in
// the file licenses/APL2.txt.
package moss
import (
"sync"
"sync/atomic"
)
// A segmentStack is a stack of segments, where higher (later) entries
// in the stack have higher precedence, and should "shadow" any
// entries of the same key from lower in the stack. A segmentStack
// implements the Snapshot interface.
type segmentStack struct {
options *CollectionOptions
stats *CollectionStats
a []Segment
m sync.Mutex // Protects the fields the follow.
refs int
lowerLevelSnapshot *SnapshotWrapper
// incarNum represents this segmentStack's unique incarnation number assigned
// when the child collection was created. 0 for top-level collection.
incarNum uint64
// childSegStacks recursively store child collection segmentStacks.
childSegStacks map[string]*segmentStack
}
func (ss *segmentStack) addRef() {
ss.m.Lock()
ss.refs++
ss.m.Unlock()
}
func (ss *segmentStack) decRef() {
ss.m.Lock()
ss.refs--
if ss.refs <= 0 {
if ss.stats != nil { // Only update stats if snapshot is on collection.
atomic.AddUint64(&ss.stats.TotSnapshotInternalClose, 1)
}
if ss.lowerLevelSnapshot != nil {
ss.lowerLevelSnapshot.Close()
ss.lowerLevelSnapshot = nil
}
}
ss.m.Unlock()
}
// ------------------------------------------------------
// Close releases associated resources.
func (ss *segmentStack) Close() error {
if ss != nil {
ss.decRef()
}
return nil
}
// ------------------------------------------------------
// Get retrieves a val from a segmentStack.
func (ss *segmentStack) Get(key []byte, readOptions ReadOptions) ([]byte, error) {
return ss.get(key, len(ss.a)-1, nil, readOptions)
}
// get() retrieves a val from a segmentStack, but only considers
// segments at or below the segStart level. The optional base
// segmentStack, when non-nil, is used instead of the
// lowerLevelSnapshot, as a form of controllable chaining.
func (ss *segmentStack) get(key []byte, segStart int, base *segmentStack,
readOptions ReadOptions) ([]byte, error) {
if segStart >= 0 {
ss.ensureSorted(0, segStart)
for seg := segStart; seg >= 0; seg-- {
b := ss.a[seg]
op, val, err := b.Get(key)
if err != nil {
return nil, err
}
if val != nil {
if op == OperationDel {
return nil, nil
}
if op == OperationMerge {
return ss.getMerged(key, val, seg-1, base, readOptions)
}
return val, nil
}
}
}
if base != nil {
return base.Get(key, readOptions)
}
if !readOptions.SkipLowerLevel && ss.lowerLevelSnapshot != nil {
return ss.lowerLevelSnapshot.Get(key, readOptions)
} // TODO: else add a special return error indicating cache-miss!
return nil, nil
}
// ------------------------------------------------------
// getMerged() retrieves a lower level val for a given key and returns
// a merged val, based on the configured merge operator.
func (ss *segmentStack) getMerged(key, val []byte, segStart int,
base *segmentStack, readOptions ReadOptions) ([]byte, error) {
var mo MergeOperator
if ss.options != nil {
mo = ss.options.MergeOperator
}
if mo == nil {
return nil, ErrMergeOperatorNil
}
vLower, err := ss.get(key, segStart, base, readOptions)
if err != nil {
return nil, err
}
vMerged, ok := mo.FullMerge(key, vLower, [][]byte{val})
if !ok {
return nil, ErrMergeOperatorFullMergeFailed
}
return vMerged, nil
}
// ------------------------------------------------------
func (ss *segmentStack) ensureSorted(minSeg, maxSeg int) {
if ss.options == nil || !ss.options.DeferredSort {
return
}
sorted := true // Two phases allows for more concurrent sorting.
for seg := maxSeg; seg >= minSeg; seg-- {
sorted = sorted && ss.a[seg].RequestSort(false)
}
if !sorted {
for seg := maxSeg; seg >= minSeg; seg-- {
ss.a[seg].RequestSort(true)
}
}
}
// ------------------------------------------------------
// SegmentStackStats represents the stats for a segmentStack.
type SegmentStackStats struct {
CurOps uint64
CurBytes uint64 // Counts key-val bytes only, not metadata.
CurSegments uint64
}
// AddTo adds the values from this SegmentStackStats to the dest
// SegmentStackStats.
func (sss *SegmentStackStats) AddTo(dest *SegmentStackStats) {
if sss == nil {
return
}
dest.CurOps += sss.CurOps
dest.CurBytes += sss.CurBytes
dest.CurSegments += sss.CurSegments
}
// Stats returns the stats for this segment stack.
func (ss *segmentStack) Stats() *SegmentStackStats {
rv := &SegmentStackStats{CurSegments: uint64(len(ss.a))}
for _, seg := range ss.a {
rv.CurOps += uint64(seg.Len())
nk, nv := seg.NumKeyValBytes()
rv.CurBytes += nk + nv
}
return rv
}
// ChildCollectionNames returns an array of child collection name strings.
func (ss *segmentStack) ChildCollectionNames() ([]string, error) {
var childCollections = make([]string, len(ss.childSegStacks))
idx := 0
for name := range ss.childSegStacks {
childCollections[idx] = name
idx++
}
return childCollections, nil
}
// ChildCollectionSnapshot returns a Snapshot on a given child
// collection by its name.
func (ss *segmentStack) ChildCollectionSnapshot(childCollectionName string) (
Snapshot, error) {
if ss.childSegStacks == nil {
return nil, nil
}
childSegStack, exists := ss.childSegStacks[childCollectionName]
if !exists {
return nil, nil
}
childSegStack.addRef()
return childSegStack, nil
}
// ensureFullySorted recursively ensures that all child segmentStacks
// are sorted from 0 to end.
func (ss *segmentStack) ensureFullySorted() {
ss.ensureSorted(0, len(ss.a)-1)
for _, childSnapshot := range ss.childSegStacks {
childSnapshot.ensureFullySorted()
}
}
func (ss *segmentStack) isEmpty() bool {
if len(ss.a) > 0 {
return false
}
for _, childSegStack := range ss.childSegStacks {
if !childSegStack.isEmpty() {
return false
}
}
return true
}