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index.go
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index.go
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package pogreb
import (
"github.com/akrylysov/pogreb/internal/errors"
)
const (
indexExt = ".pix"
indexMainName = "main" + indexExt
indexOverflowName = "overflow" + indexExt
indexMetaName = "index" + metaExt
loadFactor = 0.7
)
// index is an on-disk linear hashing hash table.
// It uses two files to store the hash table on disk - "main" and "overflow" index files.
// Each index file holds an array of buckets.
type index struct {
opts *Options
main *file // Main index file.
overflow *file // Overflow index file.
freeBucketOffs []int64 // Offsets of freed buckets.
level uint8 // Maximum number of buckets on a logarithmic scale.
numKeys uint32 // Number of keys.
numBuckets uint32 // Number of buckets.
splitBucketIdx uint32 // Index of the bucket to split on next split.
}
type indexMeta struct {
Level uint8
NumKeys uint32
NumBuckets uint32
SplitBucketIndex uint32
FreeOverflowBuckets []int64
}
// matchKeyFunc returns whether the slot matches the key sought.
type matchKeyFunc func(slot) (bool, error)
func openIndex(opts *Options) (*index, error) {
main, err := openFile(opts.FileSystem, indexMainName, openFileFlags{})
if err != nil {
return nil, errors.Wrap(err, "opening main index")
}
overflow, err := openFile(opts.FileSystem, indexOverflowName, openFileFlags{})
if err != nil {
_ = main.Close()
return nil, errors.Wrap(err, "opening overflow index")
}
idx := &index{
opts: opts,
main: main,
overflow: overflow,
numBuckets: 1,
}
if main.empty() {
// Add an empty bucket.
if _, err = idx.main.extend(bucketSize); err != nil {
_ = main.Close()
_ = overflow.Close()
return nil, err
}
} else if err := idx.readMeta(); err != nil {
_ = main.Close()
_ = overflow.Close()
return nil, errors.Wrap(err, "opening index meta")
}
return idx, nil
}
func (idx *index) writeMeta() error {
m := indexMeta{
Level: idx.level,
NumKeys: idx.numKeys,
NumBuckets: idx.numBuckets,
SplitBucketIndex: idx.splitBucketIdx,
FreeOverflowBuckets: idx.freeBucketOffs,
}
return writeGobFile(idx.opts.FileSystem, indexMetaName, m)
}
func (idx *index) readMeta() error {
m := indexMeta{}
if err := readGobFile(idx.opts.FileSystem, indexMetaName, &m); err != nil {
return err
}
idx.level = m.Level
idx.numKeys = m.NumKeys
idx.numBuckets = m.NumBuckets
idx.splitBucketIdx = m.SplitBucketIndex
idx.freeBucketOffs = m.FreeOverflowBuckets
return nil
}
func (idx *index) bucketIndex(hash uint32) uint32 {
bidx := hash & ((1 << idx.level) - 1)
if bidx < idx.splitBucketIdx {
return hash & ((1 << (idx.level + 1)) - 1)
}
return bidx
}
type bucketIterator struct {
off int64 // Offset of the next bucket.
f *file // Current index file.
overflow *file // Overflow index file.
}
// bucketOffset returns on-disk bucket offset by the bucket index.
func bucketOffset(idx uint32) int64 {
return int64(headerSize) + (int64(bucketSize) * int64(idx))
}
func (idx *index) newBucketIterator(startBucketIdx uint32) *bucketIterator {
return &bucketIterator{
off: bucketOffset(startBucketIdx),
f: idx.main,
overflow: idx.overflow,
}
}
func (it *bucketIterator) next() (bucketHandle, error) {
if it.off == 0 {
return bucketHandle{}, ErrIterationDone
}
b := bucketHandle{file: it.f, offset: it.off}
if err := b.read(); err != nil {
return bucketHandle{}, err
}
it.f = it.overflow
it.off = b.next
return b, nil
}
func (idx *index) get(hash uint32, matchKey matchKeyFunc) error {
it := idx.newBucketIterator(idx.bucketIndex(hash))
for {
b, err := it.next()
if err == ErrIterationDone {
return nil
}
if err != nil {
return err
}
for i := 0; i < slotsPerBucket; i++ {
sl := b.slots[i]
// No more slots in the bucket.
if sl.offset == 0 {
break
}
if hash != sl.hash {
continue
}
if match, err := matchKey(sl); match || err != nil {
return err
}
}
}
}
func (idx *index) findInsertionBucket(newSlot slot, matchKey matchKeyFunc) (*slotWriter, bool, error) {
sw := &slotWriter{}
it := idx.newBucketIterator(idx.bucketIndex(newSlot.hash))
for {
b, err := it.next()
if err == ErrIterationDone {
return nil, false, errors.New("failed to insert a new slot")
}
if err != nil {
return nil, false, err
}
sw.bucket = &b
var i int
for i = 0; i < slotsPerBucket; i++ {
sl := b.slots[i]
if sl.offset == 0 {
// Found an empty slot.
sw.slotIdx = i
return sw, false, nil
}
if newSlot.hash != sl.hash {
continue
}
match, err := matchKey(sl)
if err != nil {
return nil, false, err
}
if match {
// Key already in the index.
// The slot writer will overwrite the existing slot.
sw.slotIdx = i
return sw, true, nil
}
}
if b.next == 0 {
// No more buckets in the chain.
sw.slotIdx = i
return sw, false, nil
}
}
}
func (idx *index) put(newSlot slot, matchKey matchKeyFunc) error {
if idx.numKeys == MaxKeys {
return errFull
}
sw, overwritingExisting, err := idx.findInsertionBucket(newSlot, matchKey)
if err != nil {
return err
}
if err := sw.insert(newSlot, idx); err != nil {
return err
}
if err := sw.write(); err != nil {
return err
}
if overwritingExisting {
return nil
}
idx.numKeys++
if float64(idx.numKeys)/float64(idx.numBuckets*slotsPerBucket) > loadFactor {
if err := idx.split(); err != nil {
return err
}
}
return nil
}
func (idx *index) delete(hash uint32, matchKey matchKeyFunc) error {
it := idx.newBucketIterator(idx.bucketIndex(hash))
for {
b, err := it.next()
if err == ErrIterationDone {
return nil
}
if err != nil {
return err
}
for i := 0; i < slotsPerBucket; i++ {
sl := b.slots[i]
if sl.offset == 0 {
break
}
if hash != sl.hash {
continue
}
match, err := matchKey(sl)
if err != nil {
return err
}
if !match {
continue
}
b.del(i)
if err := b.write(); err != nil {
return err
}
idx.numKeys--
return nil
}
}
}
func (idx *index) createOverflowBucket() (*bucketHandle, error) {
var off int64
if len(idx.freeBucketOffs) > 0 {
off = idx.freeBucketOffs[0]
idx.freeBucketOffs = idx.freeBucketOffs[1:]
} else {
var err error
off, err = idx.overflow.extend(bucketSize)
if err != nil {
return nil, err
}
}
return &bucketHandle{file: idx.overflow, offset: off}, nil
}
func (idx *index) freeOverflowBucket(offsets ...int64) {
idx.freeBucketOffs = append(idx.freeBucketOffs, offsets...)
}
func (idx *index) split() error {
updatedBucketIdx := idx.splitBucketIdx
updatedBucketOff := bucketOffset(updatedBucketIdx)
updatedBucket := slotWriter{
bucket: &bucketHandle{file: idx.main, offset: updatedBucketOff},
}
newBucketOff, err := idx.main.extend(bucketSize)
if err != nil {
return err
}
sw := slotWriter{
bucket: &bucketHandle{file: idx.main, offset: newBucketOff},
}
idx.splitBucketIdx++
if idx.splitBucketIdx == 1<<idx.level {
idx.level++
idx.splitBucketIdx = 0
}
var overflowBuckets []int64
it := idx.newBucketIterator(updatedBucketIdx)
for {
b, err := it.next()
if err == ErrIterationDone {
break
}
if err != nil {
return err
}
for j := 0; j < slotsPerBucket; j++ {
sl := b.slots[j]
if sl.offset == 0 {
break
}
if idx.bucketIndex(sl.hash) == updatedBucketIdx {
if err := updatedBucket.insert(sl, idx); err != nil {
return err
}
} else {
if err := sw.insert(sl, idx); err != nil {
return err
}
}
}
if b.next != 0 {
overflowBuckets = append(overflowBuckets, b.next)
}
}
idx.freeOverflowBucket(overflowBuckets...)
if err := sw.write(); err != nil {
return err
}
if err := updatedBucket.write(); err != nil {
return err
}
idx.numBuckets++
return nil
}
func (idx *index) close() error {
if err := idx.writeMeta(); err != nil {
return err
}
if err := idx.main.Close(); err != nil {
return err
}
if err := idx.overflow.Close(); err != nil {
return err
}
return nil
}
func (idx *index) count() uint32 {
return idx.numKeys
}