/usr/share/gocode/src/github.com/couchbase/moss/collection.go is in golang-github-couchbase-moss-dev 0.0~git20170914.0.07c86e8-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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// 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, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
// express or implied. See the License for the specific language
// governing permissions and limitations under the License.
package moss
import (
"fmt"
"sync"
"sync/atomic"
"time"
"github.com/couchbase/ghistogram"
)
// A collection implements the Collection interface.
type collection struct {
options *CollectionOptions
stopCh chan struct{}
pingMergerCh chan ping
doneMergerCh chan struct{}
donePersisterCh chan struct{}
idleMergerTimer *time.Timer
idleMergeAlreadyDone bool
m sync.Mutex // Protects the fields that follow.
// When ExecuteBatch() has pushed a new segment onto
// stackDirtyTop, it can notify waiters like the merger via
// waitDirtyIncomingCh (if non-nil).
waitDirtyIncomingCh chan struct{}
// When the persister has finished a persistence cycle, it can
// notify waiters like the merger via waitDirtyOutgoingCh (if
// non-nil).
waitDirtyOutgoingCh chan struct{}
// stats leverage sync/atomic counters.
// All child collections simply point back to the same stats instance.
// TODO: Have child collection specific stats.
stats *CollectionStats
// latestSnapshot caches the most recent collection snapshot to avoid
// new snapshot creations in the absence of new mutations.
latestSnapshot Snapshot
// highestIncarNum is the highest descendant collection
// incarnation number seen by this collection hierarchy. It
// monotonically increases every time a new child collection is
// created and helps distinguish child collection recreations with
// the same name.
highestIncarNum uint64
// ----------------------------------------
// stackDirtyTopCond is used to wait for space in stackDirtyTop.
stackDirtyTopCond *sync.Cond
// stackDirtyBaseCond is used to wait for non-nil stackDirtyBase.
stackDirtyBaseCond *sync.Cond
// ----------------------------------------
// ExecuteBatch() will push new segments onto stackDirtyTop if
// there is space.
stackDirtyTop *segmentStack
// The merger goroutine asynchronously, atomically grabs all
// segments from stackDirtyTop and atomically moves them into
// stackDirtyMid. The merger will also merge segments in
// stackDirtyMid to keep its height low.
stackDirtyMid *segmentStack
// stackDirtyBase represents the segments currently being
// persisted. It is optionally populated by the merger when there
// are merged segments ready for persistence. Will be nil when
// persistence is not being used.
stackDirtyBase *segmentStack
// stackClean represents the segments that have been optionally
// persisted by the persister, and can now be safely evicted, as
// the lowerLevelSnapshot will contain the entries from
// stackClean. Will be nil when persistence is not being used.
stackClean *segmentStack
// lowerLevelSnapshot provides an optional, lower-level storage
// implementation, when using the Collection as a cache.
lowerLevelSnapshot *SnapshotWrapper
// histograms from collection operations
histograms ghistogram.Histograms
// incarNum is a unique incarnation number assigned to this child
// collection at the time of its creation. It helps process child
// collection recreations and is zero in the top-level collection.
incarNum uint64
// Map of child collection by name.
// TODO: Most of the fields of the child collections are nil, so
// it might be lighter to use a dedicated struct instead of
// reusing the collection struct.
childCollections map[string]*collection
}
// ------------------------------------------------------
// Start kicks off required background gouroutines.
func (m *collection) Start() error {
if !m.options.ReadOnly {
// Kick off merger and persister only when not in Read-Only mode
go m.runMerger()
go m.runPersister()
}
return nil
}
// Close synchronously stops background goroutines.
func (m *collection) Close() error {
m.fireEvent(EventKindCloseStart, 0)
startTime := time.Now()
defer func() {
m.fireEvent(EventKindClose, time.Now().Sub(startTime))
}()
atomic.AddUint64(&m.stats.TotCloseBeg, 1)
m.m.Lock()
close(m.stopCh)
m.stackDirtyTopCond.Broadcast() // Awake all ExecuteBatch()'ers.
m.stackDirtyBaseCond.Broadcast() // Awake persister.
if !m.options.ReadOnly {
m.m.Unlock()
<-m.doneMergerCh
atomic.AddUint64(&m.stats.TotCloseMergerDone, 1)
<-m.donePersisterCh
atomic.AddUint64(&m.stats.TotClosePersisterDone, 1)
m.m.Lock()
}
if m.lowerLevelSnapshot != nil {
atomic.AddUint64(&m.stats.TotCloseLowerLevelBeg, 1)
m.lowerLevelSnapshot.Close()
m.lowerLevelSnapshot = nil
atomic.AddUint64(&m.stats.TotCloseLowerLevelEnd, 1)
}
stackDirtyTopPrev := m.stackDirtyTop
m.stackDirtyTop = nil
stackDirtyMidPrev := m.stackDirtyMid
m.stackDirtyMid = nil
stackDirtyBasePrev := m.stackDirtyBase
m.stackDirtyBase = nil
stackCleanPrev := m.stackClean
m.stackClean = nil
m.m.Unlock()
stackDirtyTopPrev.Close()
stackDirtyMidPrev.Close()
stackDirtyBasePrev.Close()
stackCleanPrev.Close()
atomic.AddUint64(&m.stats.TotCloseEnd, 1)
return nil
}
func (m *collection) isClosed() bool {
select {
case <-m.stopCh:
return true
default:
return false
}
}
// Options returns the current options.
func (m *collection) Options() CollectionOptions {
return *m.options
}
// reuseSnapshot addRef()'s the underlying segmentStack.
func reuseSnapshot(snap Snapshot) Snapshot {
if snap != nil {
ss, ok := snap.(*segmentStack)
if ok {
ss.addRef()
return snap
}
}
return nil
}
// Snapshot returns a stable snapshot of the key-value entries.
func (m *collection) Snapshot() (rv Snapshot, err error) {
m.m.Lock()
rv = reuseSnapshot(m.latestSnapshot)
if rv == nil { // No cached snapshot.
rv, err = m.newSnapshotLOCKED()
if err == nil {
// collection holds 1 ref count for its cached snapshot copy.
m.latestSnapshot = reuseSnapshot(rv)
}
}
m.m.Unlock()
return
}
// invalidateLatestSnapshotLOCKED is invoked whenever new mutations or
// internal modifications (merges/persistence) occur.
func (m *collection) invalidateLatestSnapshotLOCKED() {
if m.latestSnapshot != nil {
m.latestSnapshot.Close()
m.latestSnapshot = nil
}
}
// newSnapshotLOCKED creates a new stable snapshot of the key-value
// entries.
func (m *collection) newSnapshotLOCKED() (Snapshot, error) {
if m.isClosed() {
return nil, ErrClosed
}
atomic.AddUint64(&m.stats.TotSnapshotBeg, 1)
rv, _, _, _, _ := m.snapshot(0, nil, true) // collection lock already held.
atomic.AddUint64(&m.stats.TotSnapshotEnd, 1)
return rv, nil
}
// Get retrieves a value by iterating over all the segments within
// the collection, if the key is not found a nil val is returned.
func (m *collection) Get(key []byte, readOptions ReadOptions) ([]byte, error) {
if m.isClosed() {
return nil, ErrClosed
}
atomic.AddUint64(&m.stats.TotGet, 1)
val, err := m.get(key, readOptions)
if err != nil {
atomic.AddUint64(&m.stats.TotGetErr, 1)
}
return val, err
}
// NewBatch returns a new Batch instance with hinted amount of
// resources expected to be required.
func (m *collection) NewBatch(totalOps, totalKeyValBytes int) (
Batch, error) {
if m.isClosed() {
return nil, ErrClosed
}
atomic.AddUint64(&m.stats.TotNewBatch, 1)
atomic.AddUint64(&m.stats.TotNewBatchTotalOps, uint64(totalOps))
atomic.AddUint64(&m.stats.TotNewBatchTotalKeyValBytes, uint64(totalKeyValBytes))
return newBatch(m, BatchOptions{totalOps, totalKeyValBytes})
}
// ExecuteBatch atomically incorporates the provided Batch into the
// collection. The Batch instance should not be reused after
// ExecuteBatch() returns.
func (m *collection) ExecuteBatch(bIn Batch,
writeOptions WriteOptions) error {
startTime := time.Now()
defer func() {
m.fireEvent(EventKindBatchExecute, time.Now().Sub(startTime))
}()
atomic.AddUint64(&m.stats.TotExecuteBatchBeg, 1)
b, ok := bIn.(*batch)
if !ok {
atomic.AddUint64(&m.stats.TotExecuteBatchErr, 1)
return fmt.Errorf("wrong Batch implementation type")
}
if b == nil || b.isEmpty() {
atomic.AddUint64(&m.stats.TotExecuteBatchEmpty, 1)
m.histograms["ExecuteBatchUsecs"].Add(
uint64(time.Since(startTime).Nanoseconds()/1000), 1)
return nil
}
maxPreMergerBatches := m.options.MaxPreMergerBatches
if maxPreMergerBatches <= 0 {
maxPreMergerBatches =
DefaultCollectionOptions.MaxPreMergerBatches
}
if m.options.DeferredSort {
b.readyDeferredSort() // Recursively ready child batches.
} else {
b.doSort() // Recursively sort the child batches.
}
// Notify handlers that we are about to execute a batch.
m.fireEvent(EventKindBatchExecuteStart, 0)
m.m.Lock()
for m.stackDirtyTop != nil &&
len(m.stackDirtyTop.a) >= maxPreMergerBatches {
if m.isClosed() {
m.m.Unlock()
return ErrClosed
}
if m.options.DeferredSort {
go b.RequestSort() // While waiting, might as well sort.
}
atomic.AddUint64(&m.stats.TotExecuteBatchWaitBeg, 1)
m.stackDirtyTopCond.Wait()
atomic.AddUint64(&m.stats.TotExecuteBatchWaitEnd, 1)
}
if m.isClosed() { // Could have been closed while waiting.
m.m.Unlock()
return ErrClosed
}
m.invalidateLatestSnapshotLOCKED()
stackDirtyTop := m.buildStackDirtyTop(b, m.stackDirtyTop)
prevStackDirtyTop := m.stackDirtyTop
m.stackDirtyTop = stackDirtyTop
waitDirtyIncomingCh := m.waitDirtyIncomingCh
m.waitDirtyIncomingCh = nil
m.m.Unlock()
prevStackDirtyTop.Close()
if waitDirtyIncomingCh != nil {
atomic.AddUint64(&m.stats.TotExecuteBatchAwakeMergerBeg, 1)
close(waitDirtyIncomingCh)
atomic.AddUint64(&m.stats.TotExecuteBatchAwakeMergerEnd, 1)
}
atomic.AddUint64(&m.stats.TotExecuteBatchEnd, 1)
m.histograms["ExecuteBatchUsecs"].Add(
uint64(time.Since(startTime).Nanoseconds()/1000), 1)
return nil
}
// buildStackDirtyTop recursively builds a segmentStack out of a
// recursive batch with potential child batches.
// This function does a 3 way merge.
// Consider the example below:
// Incoming batch (b) existing (curStackTop) childCollections map
// / | \ / | \ / | \
// child1 child2' child4 child1 child2 child3 child1 child2 child3
// (del) (update) (new)
//
// The result is to build a new stackTop & update childCollection map as:
// returned segmentStack (rv) childCollections map
// / | \ / | \
// child2+child2' child3 child4 child2 child3 child4
func (m *collection) buildStackDirtyTop(b *batch, curStackTop *segmentStack) (
rv *segmentStack) {
numDirtyTop := 0
if curStackTop != nil {
numDirtyTop = len(curStackTop.a)
}
rv = &segmentStack{options: m.options, refs: 1}
rv.a = make([]Segment, 0, numDirtyTop+1)
if curStackTop != nil {
rv.a = append(rv.a, curStackTop.a...)
}
rv.incarNum = m.incarNum
if b != nil {
if b.Len() > 0 {
rv.a = append(rv.a, b.segment)
}
for cName, cBatch := range b.childBatches {
if cBatch == deletedChildBatchMarker { // child1 in diagram above.
delete(m.childCollections, cName)
continue
}
if len(m.childCollections) == 0 {
m.childCollections = make(map[string]*collection)
}
childCollection, exists := m.childCollections[cName]
if !exists { // Child collection being created for first time.
m.highestIncarNum++
childCollection = &collection{ // child4 in diagram above.
options: m.options,
stats: m.stats,
highestIncarNum: m.highestIncarNum,
incarNum: m.highestIncarNum,
}
m.childCollections[cName] = childCollection
}
if len(rv.childSegStacks) == 0 {
rv.childSegStacks = make(map[string]*segmentStack)
}
var prevChildSegStack *segmentStack
if curStackTop != nil && len(curStackTop.childSegStacks) > 0 {
// child2 from existing stackDirtyTop in diagram above.
prevChildSegStack = curStackTop.childSegStacks[cName]
}
// Recursively merge & build the child collection batches.
rv.childSegStacks[cName] = childCollection.buildStackDirtyTop(
cBatch, prevChildSegStack)
}
}
if curStackTop == nil {
return rv
}
// There could be child collections in existing curStackTop that
// were not in the batch, so copy over those recursively too.
for cName, childStack := range curStackTop.childSegStacks {
if len(rv.childSegStacks) == 0 {
rv.childSegStacks = make(map[string]*segmentStack)
}
if rv.childSegStacks[cName] != nil {
// This child collection was already processed as part of
continue // batch. Do not copy over to new stackDirtyTop.
}
// Else we have a child collection in existing stackDirtyTop
// that was NOT in the incoming batch.
childCollection, exists := m.childCollections[cName]
if !exists || // This child collection was deleted OR
// it was quickly recreated in the incoming batch.
childCollection.incarNum != childStack.incarNum {
continue // Do not copy over to new stackDirtyTop.
}
// Case of child3 from existing curStackTop in diagram above.
rv.childSegStacks[cName] =
childCollection.buildStackDirtyTop(nil, childStack)
}
return rv
}
// ------------------------------------------------------
// Update stats/histograms given an immutable segment.
func (m *collection) updateStats(a *segment) {
if m == nil || m.isClosed() {
return
}
m.histograms["ExecuteBatchOpsCount"].Add(uint64(a.Len()), 1)
m.histograms["ExecuteBatchBytes"].Add(a.totKeyByte+a.totValByte, 1)
recordKeyLens := func(hist ghistogram.HistogramMutator) {
for i := 0; i < len(a.kvs); i += 2 {
opklvl := a.kvs[i]
_, length, _ := decodeOpKeyLenValLen(opklvl)
hist.Add(uint64(length), 1)
}
}
recordValLens := func(hist ghistogram.HistogramMutator) {
for i := 0; i < len(a.kvs); i += 2 {
opklvl := a.kvs[i]
_, _, length := decodeOpKeyLenValLen(opklvl)
hist.Add(uint64(length), 1)
}
}
m.histograms["MutationKeyBytes"].CallSyncEx(recordKeyLens)
m.histograms["MutationValBytes"].CallSyncEx(recordValLens)
}
// ------------------------------------------------------
// Log invokes the user's configured Log callback, if any, if the
// debug levels are met.
func (m *collection) Logf(format string, a ...interface{}) {
if m.options.Debug > 0 &&
m.options.Log != nil {
m.options.Log(format, a...)
}
}
// OnError invokes the user's configured OnError callback, in which
// the application might take further action, for example, such as
// Close()'ing the Collection in order to fix underlying
// storage/resource issues.
func (m *collection) OnError(err error) {
atomic.AddUint64(&m.stats.TotOnError, 1)
if m.options.OnError != nil {
m.options.OnError(err)
}
}
func (m *collection) fireEvent(kind EventKind, dur time.Duration) {
if m.options.OnEvent != nil {
m.options.OnEvent(Event{Kind: kind, Collection: m, Duration: dur})
}
}
// ------------------------------------------------------
const snapshotSkipDirtyTop = uint32(0x00000001)
const snapshotSkipDirtyMid = uint32(0x00000002)
const snapshotSkipDirtyBase = uint32(0x00000004)
const snapshotSkipClean = uint32(0x00000008)
// snapshot() atomically clones the various stacks into a new, single
// segmentStack, controllable by skip flags, and also invokes the
// optional callback while holding the collection lock.
func (m *collection) snapshot(skip uint32, cb func(*segmentStack),
gotLock bool) (*segmentStack, int, int, int, int) {
atomic.AddUint64(&m.stats.TotSnapshotInternalBeg, 1)
rv := &segmentStack{options: m.options, refs: 1}
heightDirtyTop := 0
heightDirtyMid := 0
heightDirtyBase := 0
heightClean := 0
if !gotLock {
m.m.Lock()
}
rv.lowerLevelSnapshot = m.lowerLevelSnapshot.addRef()
if rv.lowerLevelSnapshot != nil {
rv = m.appendChildLLSnapshot(rv, rv.lowerLevelSnapshot.ss)
}
if m.stackDirtyTop != nil && (skip&snapshotSkipDirtyTop == 0) {
heightDirtyTop = len(m.stackDirtyTop.a)
}
if m.stackDirtyMid != nil && (skip&snapshotSkipDirtyMid == 0) {
heightDirtyMid = len(m.stackDirtyMid.a)
}
if m.stackDirtyBase != nil && (skip&snapshotSkipDirtyBase == 0) {
heightDirtyBase = len(m.stackDirtyBase.a)
}
if m.stackClean != nil && (skip&snapshotSkipClean == 0) {
heightClean = len(m.stackClean.a)
}
rv.a = make([]Segment, 0,
heightDirtyTop+heightDirtyMid+heightDirtyBase+heightClean)
if m.stackClean != nil && (skip&snapshotSkipClean == 0) {
rv = m.appendChildStacks(rv, m.stackClean)
}
if m.stackDirtyBase != nil && (skip&snapshotSkipDirtyBase == 0) {
rv = m.appendChildStacks(rv, m.stackDirtyBase)
}
if m.stackDirtyMid != nil && (skip&snapshotSkipDirtyMid == 0) {
rv = m.appendChildStacks(rv, m.stackDirtyMid)
}
if m.stackDirtyTop != nil && (skip&snapshotSkipDirtyTop == 0) {
rv = m.appendChildStacks(rv, m.stackDirtyTop)
}
if cb != nil {
cb(rv)
}
if !gotLock {
m.m.Unlock()
}
atomic.AddUint64(&m.stats.TotSnapshotInternalEnd, 1)
return rv, heightClean, heightDirtyBase, heightDirtyMid, heightDirtyTop
}
// get() retrieves a value by iterating over all the segment stacks,
// and then the lower level snapshot of the collection in pursuit of
// the key, if not found, a nil val is returned.
func (m *collection) get(key []byte, readOptions ReadOptions) ([]byte, error) {
// Create a pointer to the lower level snapshot by incrementing it's ref
// count and then pointers to stackClean, stackDirtyBase, stackDirtyMid
// and stackDirtyTop for the collection within lock.
m.m.Lock()
lowerLevelSnapshot := m.lowerLevelSnapshot.addRef()
stackClean := m.stackClean
stackDirtyBase := m.stackDirtyBase
stackDirtyMid := m.stackDirtyMid
stackDirtyTop := m.stackDirtyTop
m.m.Unlock()
var val []byte
var err error
// Avoid going to the lower-level snapshot for the
// stackDirtyTop/Mid/Base/Clean Get()s since their lower level
// snapshots may be modified concurrently by
// collection_merger/persister.
readOptionsSLL := readOptions
readOptionsSLL.SkipLowerLevel = true
// Look for the key-value in the collection's segment stacks
// starting with the latest (stackDirtyTop), followed by
// stackDirtyMid, stackDirtyBase, stackClean, and if still not
// found look for it in the lowerLevelSnapshot.
if stackDirtyTop != nil {
val, err = stackDirtyTop.Get(key, readOptionsSLL)
}
if val == nil && err == nil && stackDirtyMid != nil {
val, err = stackDirtyMid.Get(key, readOptionsSLL)
}
if val == nil && err == nil && stackDirtyBase != nil {
val, err = stackDirtyBase.Get(key, readOptionsSLL)
}
if val == nil && err == nil && stackClean != nil {
val, err = stackClean.Get(key, readOptionsSLL)
}
if lowerLevelSnapshot != nil {
if val == nil && err == nil {
val, err = lowerLevelSnapshot.Get(key, readOptions)
}
lowerLevelSnapshot.decRef()
}
return val, err
}
func (m *collection) getOrInitChildStack(ss *segmentStack,
childCollName string) *segmentStack {
if len(ss.childSegStacks) == 0 {
ss.childSegStacks = make(map[string]*segmentStack)
}
dstChildStack, exists := ss.childSegStacks[childCollName]
if !exists {
dstChildStack = &segmentStack{
options: m.options,
refs: 1,
incarNum: m.incarNum,
}
}
return dstChildStack
}
// appendChildLLSnapshot recursively appends lower level child snapshots.
func (m *collection) appendChildLLSnapshot(dst *segmentStack,
src Snapshot) *segmentStack {
if m.incarNum != 0 {
dst.lowerLevelSnapshot = NewSnapshotWrapper(src, nil)
}
for cName, childCollection := range m.childCollections {
dstChildStack := childCollection.getOrInitChildStack(dst, cName)
var childSnap Snapshot
if src != nil {
childSnap, _ = src.ChildCollectionSnapshot(cName)
}
dst.childSegStacks[cName] =
childCollection.appendChildLLSnapshot(dstChildStack, childSnap)
}
return dst
}
// appendChildStacks recursively appends child segment stacks.
func (m *collection) appendChildStacks(dst, src *segmentStack) *segmentStack {
if src == nil {
return dst
}
dst.a = append(dst.a, src.a...)
for cName, srcChildStack := range src.childSegStacks {
childCollection, exists := m.childCollections[cName]
if !exists || // This child collection was dropped recently, OR
// this child collection was recreated quickly.
childCollection.incarNum != srcChildStack.incarNum {
continue
}
dstChildStack := childCollection.getOrInitChildStack(dst, cName)
dst.childSegStacks[cName] =
childCollection.appendChildStacks(dstChildStack, srcChildStack)
}
return dst
}
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