/usr/share/gocode/src/github.com/couchbase/moss/segment_stack_merge.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
// calcTargetTopLevel() heuristically computes a new top level that
// the segmentStack should be merged to.
func (ss *segmentStack) calcTargetTopLevel() int {
var minMergePercentage float64
if ss.options != nil {
minMergePercentage = ss.options.MinMergePercentage
}
if minMergePercentage <= 0 {
minMergePercentage = DefaultCollectionOptions.MinMergePercentage
}
newTopLevel := 0
maxTopLevel := len(ss.a) - 2
for newTopLevel < maxTopLevel {
numX0 := ss.a[newTopLevel].Len()
numX1 := ss.a[newTopLevel+1].Len()
if (float64(numX1) / float64(numX0)) > minMergePercentage {
break
}
newTopLevel++
}
return newTopLevel
}
// ------------------------------------------------------
// merge() returns a new segmentStack, merging all the segments that
// are at the given newTopLevel and higher.
func (ss *segmentStack) merge(mergeAll bool, base *segmentStack) (
*segmentStack, uint64, error) {
newTopLevel := 0
var numFullMerges uint64
if !mergeAll {
// If we have not been asked to merge all segments,
// then heuristically calc a newTopLevel.
newTopLevel = ss.calcTargetTopLevel()
}
if newTopLevel <= 0 {
numFullMerges++
}
// ----------------------------------------------------
// First, rough estimate the bytes neeeded.
var totOps int
var totKeyBytes, totValBytes uint64
for i := newTopLevel; i < len(ss.a); i++ {
totOps += ss.a[i].Len()
nk, nv := ss.a[i].NumKeyValBytes()
totKeyBytes += nk
totValBytes += nv
}
// ----------------------------------------------------
// Next, use an iterator for the actual merge.
mergedSegment, err := newSegment(totOps, int(totKeyBytes+totValBytes))
if err != nil {
return nil, 0, err
}
err = ss.mergeInto(newTopLevel, len(ss.a), mergedSegment, base, true,
true, nil)
if err != nil {
return nil, 0, err
}
a := make([]Segment, 0, newTopLevel+1)
a = append(a, ss.a[0:newTopLevel]...)
a = append(a, mergedSegment)
rv := &segmentStack{
options: ss.options,
a: a,
refs: 1,
lowerLevelSnapshot: ss.lowerLevelSnapshot.addRef(),
incarNum: ss.incarNum,
}
// ---------------------------------------------------
// Recursively merge all the child segmentStacks with the base
// stack, dropping any deleted collections present in base but not
// in me.
for cName, childSegStack := range ss.childSegStacks {
var baseSegStack *segmentStack
if base != nil {
var exists bool
if base.childSegStacks != nil {
baseSegStack, exists = base.childSegStacks[cName]
}
if exists {
if baseSegStack.incarNum != childSegStack.incarNum {
// The base segment stack carries a child collection
// which was subsequently recreated.
baseSegStack = nil
// The dirtyBase's old segmentStacks will be closed by
// the collection merger after successful merge.
}
}
}
mergedChildStack, fullMerges, err :=
childSegStack.merge(mergeAll, baseSegStack)
if err != nil {
rv.Close()
return nil, numFullMerges, err
}
numFullMerges += fullMerges
if len(rv.childSegStacks) == 0 {
rv.childSegStacks = make(map[string]*segmentStack)
}
rv.childSegStacks[cName] = mergedChildStack
}
return rv, numFullMerges, nil
}
func (ss *segmentStack) mergeInto(minSegmentLevel, maxSegmentHeight int,
dest SegmentMutator, base *segmentStack, includeDeletions, optimizeTail bool,
cancelCh chan struct{}) error {
cancelCheckEvery := ss.options.MergerCancelCheckEvery
if cancelCheckEvery <= 0 {
cancelCheckEvery = DefaultCollectionOptions.MergerCancelCheckEvery
}
iter, err := ss.startIterator(nil, nil, IteratorOptions{
IncludeDeletions: includeDeletions,
SkipLowerLevel: true,
MinSegmentLevel: minSegmentLevel,
MaxSegmentHeight: maxSegmentHeight,
base: base,
})
if err != nil {
return err
}
defer iter.Close()
readOptions := ReadOptions{NoCopyValue: true}
OUTER:
for i := 0; true; i++ {
if cancelCh != nil && i%cancelCheckEvery == 0 {
select {
case <-cancelCh:
return ErrAborted
default:
// NO-OP.
}
}
entryEx, key, val, err := iter.CurrentEx()
if err == ErrIteratorDone {
break
}
if err != nil {
return err
}
if optimizeTail && len(iter.cursors) == 1 {
// When only 1 cursor remains, copy the remains of the
// last segment more directly instead of Next()'ing
// through the iterator.
cursor := iter.cursors[0]
var op uint64
var k, v []byte
op, k, v = cursor.sc.Current()
for op != 0 {
err = dest.Mutate(op, k, v)
if err != nil {
return err
}
err = cursor.sc.Next()
if err != nil {
break
}
op, k, v = cursor.sc.Current()
}
if err != nil && err != ErrIteratorDone {
return err
}
break OUTER
}
op := entryEx.Operation
if op == OperationMerge {
// TODO: the merge operator implementation is currently
// inefficient and not lazy enough right now.
val, err = ss.get(key, len(ss.a)-1, base, readOptions)
if err != nil {
return err
}
if val == nil {
op = OperationDel
} else {
op = OperationSet
}
}
err = dest.Mutate(op, key, val)
if err != nil {
return err
}
err = iter.Next()
if err == ErrIteratorDone {
break
}
if err != nil {
return err
}
}
return nil
}
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