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iterator.go
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iterator.go
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// Copyright (C) 2015 Foursquare Labs Inc.
package hfile
import (
"bytes"
"encoding/binary"
"log"
"math"
)
type Iterator struct {
hfile *Reader
dataBlockIndex int
block []byte
pos int
buf []byte
key []byte
value []byte
OrderedOps
}
func NewIterator(r *Reader) *Iterator {
var buf []byte
if r.CompressionCodec > CompressionNone {
buf = make([]byte, int(float64(r.TotalUncompressedDataBytes/uint64(len(r.index)))*1.5))
}
it := Iterator{r, 0, nil, 0, buf, nil, nil, OrderedOps{nil}}
return &it
}
func (it *Iterator) Reset() {
it.dataBlockIndex = 0
it.block = nil
it.pos = 0
it.key = nil
it.value = nil
it.ResetState()
}
/*
Position the iterator at-or-after requested key by seeking forward from current position.
If already at-or-after, this is a no-op.
Otherwise, if the requested key exists, it will be positioned there, otherwise at the first key
greater than the requested one.
Returns true if, after positioning, the iterator is on a valid key (eg not at EOF), same as Next.
*/
func (it *Iterator) Seek(requested []byte) (bool, error) {
var err error
if err = it.CheckIfKeyOutOfOrder(requested); err != nil {
return false, err
}
if it.key != nil && !After(requested, it.key) {
if it.hfile.Debug {
log.Println("[Iterator.Seek] already at or past requested")
}
return true, nil
}
blk := it.hfile.FindBlock(it.dataBlockIndex, requested)
if it.hfile.Debug {
log.Printf("[Iterator.Seek] picked block %d, cur %d\n", blk, it.dataBlockIndex)
if len(it.hfile.index) > blk+1 {
log.Printf("[Iterator.Seek] following block starts at: %v\n", it.hfile.index[blk+1].firstKeyBytes)
} else {
log.Printf("[Iterator.Seek] (last block)\n")
}
}
if blk != it.dataBlockIndex { // if, and only if, FindBlock returned a block other than current.
if it.hfile.Debug {
log.Println("[Iterator.Seek] new block!")
}
it.dataBlockIndex = blk
it.block = nil // make Next load the new block.
}
ok, err := it.Next()
if err != nil {
return false, err
}
if it.hfile.Debug {
log.Printf("[Iterator.Seek] looking for %v (starting at %v)\n", requested, it.key)
}
for ok {
after := After(requested, it.key) // the key we are looking for is in our future.
if it.hfile.Debug {
log.Printf("[Iterator.Seek] \t %v (%v)\n", it.key, after)
}
if err == nil && after { // we still need to go forward.
ok, err = it.Next()
} else {
// either we got an error or we no longer need to go forward.
if it.hfile.Debug {
log.Printf("[Iterator.Seek] done %v (err %v)\n", it.key, err)
}
return ok, err
}
}
if it.hfile.Debug {
log.Println("[Iterator.Seek] walked off block")
}
return ok, err
}
/*
Load a kv pair into it.key/it.value and advance the iterator.
Return true if a kv pair was loaded (eg can call Key), or false if at EOF.
*/
func (it *Iterator) Next() (bool, error) {
var err error
it.key = nil
it.value = nil
if it.dataBlockIndex >= len(it.hfile.index) { // EOF, we're out of blocks.
return false, nil
}
if it.block == nil { // current block has not been loaded yet.
it.block, err = it.hfile.GetBlockBuf(it.dataBlockIndex, it.buf)
if err != nil {
return false, err
}
it.pos = len(DataMagic) // skip the magic bytes
}
if len(it.block)-it.pos <= 0 { // nothing left in this block to read, need a new block.
it.dataBlockIndex += 1
it.block = nil // will cause loading of the block in the next call.
return it.Next()
}
// 4 bytes each for key and value lengths, so some pointer arithmatic.
keyLen := int(binary.BigEndian.Uint32(it.block[it.pos : it.pos+4]))
valLen := int(binary.BigEndian.Uint32(it.block[it.pos+4 : it.pos+8]))
it.pos += 8
// it.pos now sitting on the begining of the key
it.key = it.block[it.pos : it.pos+keyLen]
it.value = it.block[it.pos+keyLen : it.pos+keyLen+valLen]
it.pos += keyLen + valLen // move position to next kv pair.
return true, nil
}
/*
A copy of the current key
it.key is a pointer into a buffer that may get recycled for another block, thus the copy.
*/
func (it *Iterator) Key() []byte {
ret := make([]byte, len(it.key))
copy(ret, it.key)
return ret
}
/*
A copy of the current value
it.key is a pointer into a buffer that may get recycled for another block, thus the copy.
*/
func (it *Iterator) Value() []byte {
ret := make([]byte, len(it.value))
copy(ret, it.value)
return ret
}
func (it *Iterator) AllForPrefixes(prefixes [][]byte, limit int32, lastKey []byte) (map[string][][]byte, []byte, error) {
if limit <= 0 {
limit = math.MaxInt32
}
res := make(map[string][][]byte)
values := int32(0)
var err error
preseekOk := false
if lastKey != nil {
if preseekOk, err = it.Seek(lastKey); err != nil {
return nil, nil, err
}
}
for _, prefix := range prefixes {
ok := false
if lastKey == nil || bytes.Compare(lastKey, prefix) <= 0 {
if ok, err = it.Seek(prefix); err != nil {
return nil, nil, err
}
} else {
ok = preseekOk
}
acc := make([][]byte, 0, 1)
for ok && bytes.HasPrefix(it.key, prefix) {
prev := it.key
acc = append(acc, it.Value())
if ok, err = it.Next(); err != nil {
return nil, nil, err
}
values++
if !ok || !bytes.Equal(prev, it.key) {
cp := make([]byte, len(prev))
copy(cp, prev)
res[string(cp)] = acc
acc = make([][]byte, 0, 1)
if values >= limit {
var last []byte
// reached limit and at a key boundry or end-of-file.
// We _are_ going to return now, but first may need to copy next key to `last` if it is a match.
if ok && bytes.HasPrefix(it.key, prefix) {
last = make([]byte, len(it.key))
copy(last, it.key)
}
return res, last, nil
}
}
}
if !ok {
break
}
}
return res, nil, nil
}
func (it *Iterator) Release() {
it.Reset()
select {
case it.hfile.iteratorCache <- it:
default:
}
}