/usr/share/gocode/src/github.com/couchbase/moss/store.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 (
"encoding/binary"
"encoding/json"
"fmt"
"io/ioutil"
"os"
"path"
"sort"
"strconv"
"strings"
"sync"
"time"
"github.com/couchbase/ghistogram"
)
// TODO: Improved version parsers / checkers / handling (semver?).
// StorePrefix is the file name prefix
var StorePrefix = "data-"
// StoreSuffix is the file name suffix
var StoreSuffix = ".moss"
// StoreEndian is the preferred endianness used by moss
var StoreEndian = binary.LittleEndian
// StorePageSize is the page size used by moss
var StorePageSize = 4096
// StoreVersion must be bumped whenever the file format changes.
var StoreVersion = uint32(4)
// StoreMagicBeg is the magic byte sequence at the start of a footer
var StoreMagicBeg = []byte("0m1o2s")
// StoreMagicEnd is the magic byte sequence at the end of a footer
var StoreMagicEnd = []byte("3s4p5s")
var lenMagicBeg = len(StoreMagicBeg)
var lenMagicEnd = len(StoreMagicEnd)
// footerBegLen includes StoreVersion(uint32) & footerLen(uint32).
var footerBegLen = lenMagicBeg + lenMagicBeg + 4 + 4
// footerEndLen includes footerOffset(int64) & footerLen(uint32) again.
var footerEndLen = 8 + 4 + lenMagicEnd + lenMagicEnd
// --------------------------------------------------------
// Header represents the JSON stored at the head of a file, where the
// file header bytes should be less than StorePageSize length.
type Header struct {
Version uint32 // The file format / StoreVersion.
CreatedAt string
CreatedEndian string // The endian() of the file creator.
}
// Footer represents a footer record persisted in a file, and also
// implements the moss.Snapshot interface.
type Footer struct {
m sync.Mutex // Protects the fields that follow.
refs int
SegmentLocs SegmentLocs // Persisted; older SegmentLoc's come first.
PrevFooterOffset int64 // Persisted; link for snapshot restoration.
ss *segmentStack // Ephemeral.
fileName string // Ephemeral; file name; "" when unpersisted.
filePos int64 // Ephemeral; byte offset of footer; <= 0 when unpersisted.
incarNum uint64 // Ephemeral; to detect fast collection recreations.
ChildFooters map[string]*Footer // Persisted; Child collections by name.
}
// --------------------------------------------------------
// persist helps the store implement the lower-level-update func. The
// higher snapshot may be nil.
func (s *Store) persist(higher Snapshot, persistOptions StorePersistOptions) (
Snapshot, error) {
wasCompacted, err := s.compactMaybe(higher, persistOptions)
if err != nil {
return nil, err
}
if wasCompacted {
return s.Snapshot()
}
// If no dirty higher items, we're still clean, so just snapshot.
// If in case of ReadOnly mode, just snapshot.
if higher == nil || s.Options().CollectionOptions.ReadOnly {
return s.Snapshot()
}
startTime := time.Now()
ss, ok := higher.(*segmentStack)
if !ok {
return nil, fmt.Errorf("store: can only persist segmentStack")
}
// If higher segment has no data, we're still clean, so just snapshot.
if ss.isEmpty() {
return s.Snapshot()
}
fref, file, err := s.startOrReuseFile()
if err != nil {
return nil, err
}
defer fref.DecRef()
// TODO: Pre-allocate file space up front?
// Recursively sort all child collection stacks if sorting was deferred.
ss.ensureFullySorted()
// Recursively build a new store footer combined with higher snapshot.
s.m.Lock()
footer := s.buildNewFooter(s.footer, ss)
s.m.Unlock()
// Recursively write out all the segments of the snapshot.
err = s.persistSegments(ss, footer, file, fref)
if err != nil {
return nil, err
}
// Recursively load all segments of the newly persisted footer.
err = footer.loadSegments(s.options, fref)
if err != nil {
return nil, err
}
// Recursively persist all footers of top-level and child collections.
err = s.persistFooter(file, footer, persistOptions)
if err != nil {
footer.DecRef()
return nil, err
}
footer.AddRef() // One ref-count will be held by the store.
s.m.Lock()
prevFooter := s.footer
s.footer = footer
s.totPersists++
s.m.Unlock()
s.histograms["PersistUsecs"].Add(
uint64(time.Since(startTime).Nanoseconds()/1000), 1)
if prevFooter != nil {
prevFooter.DecRef()
}
return footer, nil // The other ref-count returned to caller.
}
// buildNewFooter will construct a new Footer for the store by combining
// the given storeFooter's segmentLocs with that of the incoming snapshot.
func (s *Store) buildNewFooter(storeFooter *Footer, ss *segmentStack) *Footer {
footer := &Footer{refs: 1, incarNum: ss.incarNum}
numSegmentLocs := len(ss.a)
var segmentLocs []SegmentLoc
if storeFooter != nil {
numSegmentLocs += len(storeFooter.SegmentLocs)
segmentLocs = make([]SegmentLoc, 0, numSegmentLocs)
segmentLocs = append(segmentLocs, storeFooter.SegmentLocs...)
footer.PrevFooterOffset = storeFooter.filePos
} else {
segmentLocs = make([]SegmentLoc, 0, numSegmentLocs)
}
footer.SegmentLocs = segmentLocs
// Now process the child collections recursively.
for cName, childStack := range ss.childSegStacks {
var storeChildFooter *Footer
if storeFooter != nil && storeFooter.ChildFooters != nil {
var exists bool
storeChildFooter, exists = storeFooter.ChildFooters[cName]
if exists {
if storeChildFooter.incarNum != childStack.incarNum {
// This is a special case of deletion & recreate where an
// existing child collection has been deleted and quickly
// recreated. Here we drop the existing store footer's
// segments that correspond to the prior incarnation.
storeChildFooter = nil
}
}
}
childFooter := s.buildNewFooter(storeChildFooter, childStack)
if len(footer.ChildFooters) == 0 {
footer.ChildFooters = make(map[string]*Footer)
}
footer.ChildFooters[cName] = childFooter
}
// As a deleted Child collection does not feature in the source
// segmentStack, its corresponding Footer would simply get dropped.
return footer
}
// persistSegments will recursively write out all the segments of the
// current collection as well as any of its child collections.
func (s *Store) persistSegments(ss *segmentStack, footer *Footer,
file File, fref *FileRef) error {
// First persist the child segments recursively.
for cName, childSegStack := range ss.childSegStacks {
err := s.persistSegments(childSegStack, footer.ChildFooters[cName],
file, fref)
if err != nil {
return err
}
}
for _, segment := range ss.a {
if segment.Len() <= 0 {
// With multiple child collections it is possible that some child
// collections segments are empty. Ok to skip these empty segments.
continue
}
segmentLoc, err := s.persistSegment(file, segment, s.options)
if err != nil {
return err
}
footer.SegmentLocs = append(footer.SegmentLocs, segmentLoc)
}
return nil
}
// --------------------------------------------------------
// startOrReuseFile either creates a new file or reuses the file from
// the last/current footer.
func (s *Store) startOrReuseFile() (fref *FileRef, file File, err error) {
s.m.Lock()
defer s.m.Unlock()
if s.footer != nil {
slocs, _ := s.footer.segmentLocs()
defer s.footer.DecRef()
if len(slocs) > 0 {
fref := slocs[0].mref.fref
file := fref.AddRef()
return fref, file, nil
}
}
return s.startFileLOCKED()
}
func (s *Store) startFileLOCKED() (*FileRef, File, error) {
fname, file, err := s.createNextFileLOCKED()
if err != nil {
return nil, nil, err
}
if err = s.persistHeader(file); err != nil {
file.Close()
os.Remove(path.Join(s.dir, fname))
return nil, nil, err
}
fref := &FileRef{file: file, refs: 1}
s.fileRefMap[fname] = fref
return fref, file, nil
}
func (s *Store) createNextFileLOCKED() (string, File, error) {
// File to be opened in RDWR mode here because this is either
// invoked by the persister or the compactor either of which
// do not execute in the ReadOnly mode
fname := FormatFName(s.nextFNameSeq)
s.nextFNameSeq++
file, err := s.options.OpenFile(path.Join(s.dir, fname),
os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
return "", nil, err
}
return fname, file, nil
}
// removeFileOnClose will setup the callback to wipe out the file safely
// when all references to it are closed.
func (s *Store) removeFileOnClose(fref *FileRef) (os.FileInfo, error) {
finfo, err := fref.file.Stat()
if err != nil {
return nil, err
}
if len(finfo.Name()) > 0 {
fref.OnAfterClose(func() {
fileName := finfo.Name()
go func() {
s.m.Lock()
delete(s.fileRefMap, fileName)
s.m.Unlock()
err := os.Remove(path.Join(s.dir, fileName))
if err != nil {
if s.options.CollectionOptions.Log != nil {
s.options.CollectionOptions.Log(
"store: error deleting file %s, err: %v",
fileName, err)
}
}
}()
})
}
return finfo, nil
}
// --------------------------------------------------------
// Fetch all the files within the store, and the number of those
// files that are open/in-use.
func (s *Store) allFiles() (map[string]interface{}, int) {
files := make(map[string]interface{})
s.m.Lock()
for filename, ref := range s.fileRefMap {
if ref != nil {
files[filename] =
map[string]interface{}{"ref_count": ref.FetchRefCount()}
}
}
s.m.Unlock()
numFilesOpen := len(files)
fd, err := os.Open(s.dir)
if err == nil {
filelist, err := fd.Readdir(-1)
fd.Close()
if err == nil {
for _, finfo := range filelist {
fileEntry := map[string]interface{}{"ref_count": nil,
"file_size": finfo.Size(),
"file_mode": finfo.Mode(),
"file_modified": finfo.ModTime(),
"is_dir": finfo.IsDir()}
referencedEntry, exists := files[finfo.Name()]
if exists {
refMap, _ := referencedEntry.(map[string]interface{})
fileEntry["ref_count"] = refMap["ref_count"]
}
files[finfo.Name()] = fileEntry
}
}
}
return files, numFilesOpen
}
// --------------------------------------------------------
// HeaderLength returns the length of the header
func HeaderLength() uint64 {
return uint64(StorePageSize)
}
func (s *Store) persistHeader(file File) error {
buf, err := json.Marshal(Header{
Version: StoreVersion,
CreatedAt: time.Now().Format(time.RFC3339),
CreatedEndian: endian(),
})
if err != nil {
return err
}
str := "moss-data-store:\n" + string(buf) + "\n"
if len(str) >= StorePageSize {
return fmt.Errorf("store: header size too big")
}
str = str + strings.Repeat("\n", StorePageSize-len(str))
n, err := file.WriteAt([]byte(str), 0)
if err != nil {
return err
}
if n != len(str) {
return fmt.Errorf("store: could not write full header")
}
return nil
}
func checkHeader(file File) error {
buf := make([]byte, StorePageSize)
n, err := file.ReadAt(buf, int64(0))
if err != nil {
return err
}
if n != len(buf) {
return fmt.Errorf("store: readHeader too short")
}
lines := strings.Split(string(buf), "\n")
if len(lines) < 2 {
return fmt.Errorf("store: readHeader not enough lines")
}
if lines[0] != "moss-data-store:" {
return fmt.Errorf("store: readHeader wrong file prefix")
}
hdr := Header{}
err = json.Unmarshal([]byte(lines[1]), &hdr)
if err != nil {
return err
}
if hdr.Version != StoreVersion {
return fmt.Errorf("store: readHeader wrong version")
}
if hdr.CreatedEndian != endian() {
return fmt.Errorf("store: readHeader endian of file was: %s, need: %s",
hdr.CreatedEndian, endian())
}
return nil
}
// --------------------------------------------------------
func (s *Store) persistSegment(file File, segIn Segment,
options *StoreOptions) (rv SegmentLoc, err error) {
segPersister, ok := segIn.(SegmentPersister)
if !ok {
return rv, fmt.Errorf("store: can only persist SegmentPersister type")
}
if s.IsAborted() {
return rv, ErrAborted
}
return segPersister.Persist(file, options)
}
// --------------------------------------------------------
// ParseFNameSeq parses a file name like "data-000123.moss" into 123.
func ParseFNameSeq(fname string) (int64, error) {
if len(StorePrefix) > len(fname)-len(StoreSuffix) {
return 0, fmt.Errorf("store: invalid filename: %s, filename too short", fname)
}
seqStr := fname[len(StorePrefix) : len(fname)-len(StoreSuffix)]
return strconv.ParseInt(seqStr, 16, 64)
}
// FormatFName returns a file name like "data-000123.moss" given a seq of 123.
func FormatFName(seq int64) string {
return fmt.Sprintf("%s%016x%s", StorePrefix, seq, StoreSuffix)
}
// --------------------------------------------------------
// pageAlignCeil returns the pos if it's at the start of a page.
// Else, pageAlignCeil() returns pos bumped up to the next multiple
// of StorePageSize.
func pageAlignCeil(pos int64) int64 {
rem := pos % int64(StorePageSize)
if rem != 0 {
return pos + int64(StorePageSize) - rem
}
return pos
}
// pageAlignFloor returns the pos if it's at the start of a page.
// Else, pageAlignFloor() returns pos bumped down to the previous
// multiple of StorePageSize.
func pageAlignFloor(pos int64) int64 {
rem := pos % int64(StorePageSize)
if rem != 0 {
return pos - rem
}
return pos
}
// pageOffset returns the page offset for a given pos.
func pageOffset(pos, pageSize int64) int64 {
rem := pos % pageSize
if rem != 0 {
return pos - rem
}
return pos
}
// --------------------------------------------------------
func openStore(dir string, options StoreOptions) (*Store, error) {
fileInfos, err := ioutil.ReadDir(dir)
if err != nil {
return nil, err
}
var maxFNameSeq int64
var fnames []string
for _, fileInfo := range fileInfos { // Find candidate file names.
fname := fileInfo.Name()
if strings.HasPrefix(fname, StorePrefix) &&
strings.HasSuffix(fname, StoreSuffix) {
fnames = append(fnames, fname)
}
fnameSeq, err := ParseFNameSeq(fname)
if err == nil && fnameSeq > maxFNameSeq {
maxFNameSeq = fnameSeq
}
}
if options.OpenFile == nil {
options.OpenFile =
func(name string, flag int, perm os.FileMode) (File, error) {
return os.OpenFile(name, flag, perm)
}
}
histograms := make(ghistogram.Histograms)
histograms["PersistFooterUsecs"] =
ghistogram.NewNamedHistogram("PersistFooterUsecs", 10, 4, 4)
histograms["PersistUsecs"] =
ghistogram.NewNamedHistogram("PersistUsecs", 10, 4, 4)
histograms["CompactUsecs"] =
ghistogram.NewNamedHistogram("CompactUsecs", 10, 4, 4)
if len(fnames) <= 0 {
emptyFooter := &Footer{
refs: 1,
ss: &segmentStack{options: &options.CollectionOptions},
ChildFooters: make(map[string]*Footer),
}
return &Store{
dir: dir,
options: &options,
refs: 1,
footer: emptyFooter,
nextFNameSeq: 1,
histograms: histograms,
fileRefMap: make(map[string]*FileRef),
abortCh: make(chan struct{}),
}, nil
}
sort.Strings(fnames)
for i := len(fnames) - 1; i >= 0; i-- {
var flag int
var perm os.FileMode
if options.CollectionOptions.ReadOnly {
flag = os.O_RDONLY
perm = 0400
} else {
flag = os.O_RDWR
perm = 0600
}
file, err := options.OpenFile(path.Join(dir, fnames[i]), flag, perm)
if err != nil {
continue
}
err = checkHeader(file)
if err != nil {
file.Close()
return nil, err
}
// Will recursively restore ChildFooters of childCollections
footer, err := ReadFooter(&options, file) // Footer owns file on success.
if err != nil {
file.Close()
continue
}
if !options.KeepFiles {
err := removeFiles(dir, append(fnames[0:i], fnames[i+1:]...))
if err != nil {
footer.Close()
return nil, err
}
}
return &Store{
dir: dir,
options: &options,
refs: 1,
footer: footer,
nextFNameSeq: maxFNameSeq + 1,
histograms: histograms,
fileRefMap: make(map[string]*FileRef),
abortCh: make(chan struct{}),
}, nil
}
return nil, fmt.Errorf("store: could not open/parse"+
" any file, dir: %s", dir)
}
// --------------------------------------------------------
func (s *Store) openCollection(
options StoreOptions,
persistOptions StorePersistOptions) (Collection, error) {
storeSnapshotInit, err := s.Snapshot()
if err != nil {
return nil, err
}
co := options.CollectionOptions
co.LowerLevelInit = storeSnapshotInit
co.LowerLevelUpdate = func(higher Snapshot) (Snapshot, error) {
var ss Snapshot
var erro error
ss, erro = s.Persist(higher, persistOptions)
if erro != nil {
return nil, erro
}
if storeSnapshotInit != nil {
storeSnapshotInit.Close()
storeSnapshotInit = nil
}
return ss, erro
}
storeFooter, ok := storeSnapshotInit.(*Footer)
if !ok {
storeSnapshotInit.Close()
return nil, fmt.Errorf("store: wrong storeSnapshotInit type")
}
coll, err := restoreCollection(&co, storeFooter)
if err != nil {
storeSnapshotInit.Close()
return nil, err
}
err = coll.Start()
if err != nil {
storeSnapshotInit.Close()
return nil, err
}
return coll, nil
}
// statsReporter interface represents stats reporting methods.
type statsReporter interface {
reportBytesWritten(numBytesWritten uint64)
}
func (s *Store) reportBytesWritten(numBytesWritten uint64) {
s.m.Lock()
s.totCompactionWrittenBytes += numBytesWritten
s.m.Unlock()
}
func restoreCollection(co *CollectionOptions, storeFooter *Footer) (
rv *collection, err error) {
var coll *collection
if storeFooter.incarNum == 0 {
var newColl Collection
newColl, err = NewCollection(*co)
if err != nil {
return nil, err
}
var ok bool
coll, ok = newColl.(*collection)
if !ok {
return nil, fmt.Errorf("store: wrong collection type")
}
} else {
coll = &collection{
options: co,
stats: &CollectionStats{},
incarNum: storeFooter.incarNum,
}
}
coll.highestIncarNum = coll.incarNum
for collName, childFooter := range storeFooter.ChildFooters {
if len(coll.childCollections) == 0 {
coll.childCollections = make(map[string]*collection)
}
// Keep the incarnation numbers of the newly restored child
// collections monotonically increasing.
coll.highestIncarNum++
childFooter.incarNum = coll.highestIncarNum
var childCollection *collection
childCollection, err = restoreCollection(co, childFooter)
if err != nil {
break
}
coll.childCollections[collName] = childCollection
}
return coll, err
}
// --------------------------------------------------------
func removeFiles(dir string, fnames []string) error {
for _, fname := range fnames {
err := os.Remove(path.Join(dir, fname))
if err != nil {
return err
}
}
return nil
}
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