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index.go
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index.go
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package wal
import (
logger "code.google.com/p/log4go"
"fmt"
"io/ioutil"
"os"
"sort"
"strconv"
"strings"
)
type indexEntry struct {
FirstRequestNumber uint32 // first request number in the block
LastRequestNumber uint32 // number of requests in the block
FirstOffset int64 // the offset of the first request
LastOffset int64 // the offset of the last request
}
func (self *indexEntry) NumberOfRequests() int {
return int(self.LastRequestNumber-self.FirstRequestNumber) + 1
}
type index struct {
f *os.File
Entries []*indexEntry
}
func newIndex(path string) (*index, error) {
f, err := os.OpenFile(path, os.O_CREATE|os.O_APPEND|os.O_RDWR, 0644)
if err != nil {
return nil, err
}
stat, err := f.Stat()
if err != nil {
return nil, err
}
if stat.Size() == 0 {
// append the version, which is 1 right now
fmt.Fprintf(f, "%d\n", 1)
}
if _, err = f.Seek(0, os.SEEK_SET); err != nil {
return nil, err
}
content, err := ioutil.ReadAll(f)
if err != nil {
return nil, err
}
lines := strings.Split(string(content), "\n")
entries := make([]*indexEntry, 0, len(lines))
// skip the first line, that's the version
for _, line := range lines[1:] {
if len(line) == 0 {
break
}
fields := strings.Split(line, ",")
firstRequestNumber, _ := strconv.ParseInt(fields[0], 10, 64)
firstOffset, _ := strconv.ParseInt(fields[1], 10, 64)
lastRequestNumber, _ := strconv.ParseInt(fields[2], 10, 64)
lastOffset, _ := strconv.ParseInt(fields[3], 10, 64)
entries = append(entries, &indexEntry{
uint32(firstRequestNumber),
uint32(lastRequestNumber),
firstOffset,
lastOffset,
})
}
return &index{f, entries}, nil
}
func (self *index) addEntry(firstRequestNumber, lastRequestNumber uint32, firstOffset, lastOffset int64) {
if firstRequestNumber > lastRequestNumber {
panic(fmt.Errorf("invalid index entry: [%d,%d,%d,%d]", firstRequestNumber, lastRequestNumber, firstOffset, lastOffset))
}
logger.Debug("Adding index entry [%d,%d,%d,%d]", firstRequestNumber, lastRequestNumber, firstOffset, lastOffset)
fmt.Fprintf(self.f, "%d,%d,%d,%d\n", firstRequestNumber, firstOffset, lastRequestNumber, lastOffset)
entry := &indexEntry{
FirstRequestNumber: firstRequestNumber,
FirstOffset: firstOffset,
LastRequestNumber: lastRequestNumber,
LastOffset: lastOffset,
}
self.Entries = append(self.Entries, entry)
}
func (self *index) syncFile() error {
return self.f.Sync()
}
func (self *index) close() error {
return self.f.Close()
}
func (self *index) delete() error {
return os.Remove(self.f.Name())
}
func (self *index) getLastRequestInfo() (uint32, int64) {
if len(self.Entries) == 0 {
return 0, 0
}
lastEntry := self.Entries[len(self.Entries)-1]
return lastEntry.LastRequestNumber, lastEntry.LastOffset
}
func (self *index) getLastOffset() int64 {
if len(self.Entries) == 0 {
return 0
}
entry := self.Entries[len(self.Entries)-1]
return entry.LastOffset
}
func (self *index) getLength() int {
firstRequest, _ := self.getFirstRequestInfo()
lastRequest, _ := self.getLastRequestInfo()
return int(lastRequest - firstRequest)
}
func (self *index) getFirstRequestInfo() (uint32, int64) {
if len(self.Entries) == 0 {
return 0, 0
}
firstEntry := self.Entries[0]
return firstEntry.FirstRequestNumber, firstEntry.FirstOffset
}
func (self *index) blockSearch(requestNumber uint32) func(int) bool {
return func(i int) bool {
// The returned function must satisfy `f(i) => f(i+1)`, meaning if
// for index i f returns true, then it must return true for every
// index greater than i. sort.Search will return the smallest
// index satisfying f
return requestNumber <= self.Entries[i].LastRequestNumber
}
}
func (self *index) requestOffset(requestNumber uint32) int64 {
numberOfEntries := len(self.Entries)
if numberOfEntries == 0 {
return -1
}
firstEntry := self.Entries[0]
if requestNumber < firstEntry.FirstRequestNumber {
return -1
}
lastEntry := self.Entries[numberOfEntries-1]
if requestNumber > lastEntry.LastRequestNumber {
return -1
}
index := sort.Search(numberOfEntries, self.blockSearch(requestNumber))
return self.Entries[index].FirstOffset
}
func (self *index) requestOrLastOffset(requestNumber uint32) int64 {
numberOfEntries := len(self.Entries)
if numberOfEntries == 0 {
return 0
}
if requestNumber > self.Entries[numberOfEntries-1].LastRequestNumber {
return self.Entries[numberOfEntries-1].LastOffset
}
return self.requestOffset(requestNumber)
}