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index.go
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index.go
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package pogreb
import (
"path/filepath"
)
const (
indexExt = ".pix"
indexMainName = "main" + indexExt
indexOverflowName = "overflow" + indexExt
indexMetaName = "index" + metaExt
loadFactor = 0.7
)
// index is an on-disk linear hashing hash table.
type index struct {
opts *Options
main *file
overflow *file
freeBucketOffs []int64
level uint8
numKeys uint32
numBuckets uint32
splitBucketIdx uint32
}
type indexMeta struct {
Level uint8
NumKeys uint32
NumBuckets uint32
SplitBucketIndex uint32
FreeOverflowBuckets []int64
}
func openIndex(opts *Options) (*index, error) {
main, err := openFile(opts.FileSystem, filepath.Join(opts.path, indexMainName), false)
if err != nil {
return nil, err
}
overflow, err := openFile(opts.FileSystem, filepath.Join(opts.path, indexOverflowName), false)
if err != nil {
_ = main.Close()
return nil, err
}
idx := &index{
opts: opts,
main: main,
overflow: overflow,
numBuckets: 1,
}
if main.empty() {
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, err
}
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, filepath.Join(idx.opts.path, indexMetaName), m)
}
func (idx *index) readMeta() error {
m := indexMeta{}
if err := readGobFile(idx.opts.FileSystem, filepath.Join(idx.opts.path, 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 bucketOffset(idx uint32) int64 {
return int64(headerSize) + (int64(bucketSize) * int64(idx))
}
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
}
// TODO: deeply nested callbacks are hard to reason about.
// TODO: rewrite the function to return an iterator if there is no performance implications.
func (idx *index) forEachBucket(startBucketIdx uint32, cb func(bucketHandle) (bool, error)) error {
off := bucketOffset(startBucketIdx)
f := idx.main.MmapFile
for {
b := bucketHandle{file: f, offset: off}
if err := b.read(); err != nil {
return err
}
if stop, err := cb(b); stop || err != nil {
return err
}
if b.next == 0 {
return nil
}
off = b.next
f = idx.overflow.MmapFile
}
}
func (idx *index) get(hash uint32, cb func(slot) (bool, error)) error {
return idx.forEachBucket(idx.bucketIndex(hash), func(b bucketHandle) (bool, error) {
for i := 0; i < slotsPerBucket; i++ {
sl := b.slots[i]
if sl.offset == 0 {
return b.next == 0, nil
}
if hash == sl.hash {
if found, err := cb(sl); found || err != nil {
return found, err
}
}
}
return false, nil
})
}
func (idx *index) put(sl slot, cb func(slot) (bool, error)) error {
var b *bucketHandle
var originalB *bucketHandle
slotIdx := 0
err := idx.forEachBucket(idx.bucketIndex(sl.hash), func(curb bucketHandle) (bool, error) {
b = &curb
for i := 0; i < slotsPerBucket; i++ {
cursl := b.slots[i]
slotIdx = i
if cursl.offset == 0 {
// Found an empty slot.
return true, nil
}
if sl.hash == cursl.hash {
if found, err := cb(cursl); err != nil || found {
// Key already exists.
return found, err
}
}
}
if b.next == 0 {
// Couldn't find free space in the current bucket, create a new overflow bucket.
nextBucket, err := idx.createOverflowBucket()
if err != nil {
return false, err
}
b.next = nextBucket.offset
originalB = b
b = nextBucket
slotIdx = 0
return true, nil
}
return false, nil
})
if err != nil {
return err
}
// Inserting a new item.
if b.slots[slotIdx].offset == 0 {
if idx.numKeys == MaxKeys {
return errFull
}
idx.numKeys++
}
b.slots[slotIdx] = sl
if err := b.write(); err != nil {
return err
}
if originalB != nil {
return originalB.write()
}
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, cb func(slot) (bool, error)) error {
b := bucketHandle{}
slotIdx := -1
err := idx.forEachBucket(idx.bucketIndex(hash), func(curb bucketHandle) (bool, error) {
b = curb
for i := 0; i < slotsPerBucket; i++ {
sl := b.slots[i]
if sl.offset == 0 {
return b.next == 0, nil
}
if hash == sl.hash {
found, err := cb(sl)
if err != nil {
return true, err
}
if found {
slotIdx = i
return true, nil
}
}
}
return false, nil
})
if slotIdx == -1 || err != nil {
return err
}
b.del(slotIdx)
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
}
newBucket := slotWriter{
bucket: &bucketHandle{file: idx.main, offset: newBucketOff},
}
idx.splitBucketIdx++
if idx.splitBucketIdx == 1<<idx.level {
idx.level++
idx.splitBucketIdx = 0
}
var overflowBuckets []int64
err = idx.forEachBucket(updatedBucketIdx, func(curb bucketHandle) (bool, error) {
for j := 0; j < slotsPerBucket; j++ {
sl := curb.slots[j]
if sl.offset == 0 {
break
}
if idx.bucketIndex(sl.hash) == updatedBucketIdx {
if err := updatedBucket.insert(sl, idx); err != nil {
return true, err
}
} else {
if err := newBucket.insert(sl, idx); err != nil {
return true, err
}
}
}
if curb.next != 0 {
overflowBuckets = append(overflowBuckets, curb.next)
}
return false, nil
})
if err != nil {
return err
}
idx.freeOverflowBucket(overflowBuckets...)
if err := newBucket.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
}