meditime/vendor/github.com/dgraph-io/badger/table/iterator.go

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/*
* Copyright 2017 Dgraph Labs, Inc. and Contributors
*
* 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 table
import (
"bytes"
"io"
"math"
"sort"
"github.com/dgraph-io/badger/y"
"github.com/pkg/errors"
)
type blockIterator struct {
data []byte
pos uint32
err error
baseKey []byte
key []byte
val []byte
init bool
last header // The last header we saw.
}
func (itr *blockIterator) Reset() {
itr.pos = 0
itr.err = nil
itr.baseKey = []byte{}
itr.key = []byte{}
itr.val = []byte{}
itr.init = false
itr.last = header{}
}
func (itr *blockIterator) Init() {
if !itr.init {
itr.Next()
}
}
func (itr *blockIterator) Valid() bool {
return itr != nil && itr.err == nil
}
func (itr *blockIterator) Error() error {
return itr.err
}
func (itr *blockIterator) Close() {}
var (
origin = 0
current = 1
)
// Seek brings us to the first block element that is >= input key.
func (itr *blockIterator) Seek(key []byte, whence int) {
itr.err = nil
switch whence {
case origin:
itr.Reset()
case current:
}
var done bool
for itr.Init(); itr.Valid(); itr.Next() {
k := itr.Key()
if y.CompareKeys(k, key) >= 0 {
// We are done as k is >= key.
done = true
break
}
}
if !done {
itr.err = io.EOF
}
}
func (itr *blockIterator) SeekToFirst() {
itr.err = nil
itr.Init()
}
// SeekToLast brings us to the last element. Valid should return true.
func (itr *blockIterator) SeekToLast() {
itr.err = nil
for itr.Init(); itr.Valid(); itr.Next() {
}
itr.Prev()
}
// parseKV would allocate a new byte slice for key and for value.
func (itr *blockIterator) parseKV(h header) {
if cap(itr.key) < int(h.plen+h.klen) {
sz := int(h.plen) + int(h.klen) // Convert to int before adding to avoid uint16 overflow.
itr.key = make([]byte, 2*sz)
}
itr.key = itr.key[:h.plen+h.klen]
copy(itr.key, itr.baseKey[:h.plen])
copy(itr.key[h.plen:], itr.data[itr.pos:itr.pos+uint32(h.klen)])
itr.pos += uint32(h.klen)
if itr.pos+uint32(h.vlen) > uint32(len(itr.data)) {
itr.err = errors.Errorf("Value exceeded size of block: %d %d %d %d %v",
itr.pos, h.klen, h.vlen, len(itr.data), h)
return
}
itr.val = y.SafeCopy(itr.val, itr.data[itr.pos:itr.pos+uint32(h.vlen)])
itr.pos += uint32(h.vlen)
}
func (itr *blockIterator) Next() {
itr.init = true
itr.err = nil
if itr.pos >= uint32(len(itr.data)) {
itr.err = io.EOF
return
}
var h header
itr.pos += uint32(h.Decode(itr.data[itr.pos:]))
itr.last = h // Store the last header.
if h.klen == 0 && h.plen == 0 {
// Last entry in the table.
itr.err = io.EOF
return
}
// Populate baseKey if it isn't set yet. This would only happen for the first Next.
if len(itr.baseKey) == 0 {
// This should be the first Next() for this block. Hence, prefix length should be zero.
y.AssertTrue(h.plen == 0)
itr.baseKey = itr.data[itr.pos : itr.pos+uint32(h.klen)]
}
itr.parseKV(h)
}
func (itr *blockIterator) Prev() {
if !itr.init {
return
}
itr.err = nil
if itr.last.prev == math.MaxUint32 {
// This is the first element of the block!
itr.err = io.EOF
itr.pos = 0
return
}
// Move back using current header's prev.
itr.pos = itr.last.prev
var h header
y.AssertTruef(itr.pos < uint32(len(itr.data)), "%d %d", itr.pos, len(itr.data))
itr.pos += uint32(h.Decode(itr.data[itr.pos:]))
itr.parseKV(h)
itr.last = h
}
func (itr *blockIterator) Key() []byte {
if itr.err != nil {
return nil
}
return itr.key
}
func (itr *blockIterator) Value() []byte {
if itr.err != nil {
return nil
}
return itr.val
}
// Iterator is an iterator for a Table.
type Iterator struct {
t *Table
bpos int
bi *blockIterator
err error
// Internally, Iterator is bidirectional. However, we only expose the
// unidirectional functionality for now.
reversed bool
}
// NewIterator returns a new iterator of the Table
func (t *Table) NewIterator(reversed bool) *Iterator {
t.IncrRef() // Important.
ti := &Iterator{t: t, reversed: reversed}
ti.next()
return ti
}
// Close closes the iterator (and it must be called).
func (itr *Iterator) Close() error {
return itr.t.DecrRef()
}
func (itr *Iterator) reset() {
itr.bpos = 0
itr.err = nil
}
// Valid follows the y.Iterator interface
func (itr *Iterator) Valid() bool {
return itr.err == nil
}
func (itr *Iterator) seekToFirst() {
numBlocks := len(itr.t.blockIndex)
if numBlocks == 0 {
itr.err = io.EOF
return
}
itr.bpos = 0
block, err := itr.t.block(itr.bpos)
if err != nil {
itr.err = err
return
}
itr.bi = block.NewIterator()
itr.bi.SeekToFirst()
itr.err = itr.bi.Error()
}
func (itr *Iterator) seekToLast() {
numBlocks := len(itr.t.blockIndex)
if numBlocks == 0 {
itr.err = io.EOF
return
}
itr.bpos = numBlocks - 1
block, err := itr.t.block(itr.bpos)
if err != nil {
itr.err = err
return
}
itr.bi = block.NewIterator()
itr.bi.SeekToLast()
itr.err = itr.bi.Error()
}
func (itr *Iterator) seekHelper(blockIdx int, key []byte) {
itr.bpos = blockIdx
block, err := itr.t.block(blockIdx)
if err != nil {
itr.err = err
return
}
itr.bi = block.NewIterator()
itr.bi.Seek(key, origin)
itr.err = itr.bi.Error()
}
// seekFrom brings us to a key that is >= input key.
func (itr *Iterator) seekFrom(key []byte, whence int) {
itr.err = nil
switch whence {
case origin:
itr.reset()
case current:
}
idx := sort.Search(len(itr.t.blockIndex), func(idx int) bool {
ko := itr.t.blockIndex[idx]
return y.CompareKeys(ko.key, key) > 0
})
if idx == 0 {
// The smallest key in our table is already strictly > key. We can return that.
// This is like a SeekToFirst.
itr.seekHelper(0, key)
return
}
// block[idx].smallest is > key.
// Since idx>0, we know block[idx-1].smallest is <= key.
// There are two cases.
// 1) Everything in block[idx-1] is strictly < key. In this case, we should go to the first
// element of block[idx].
// 2) Some element in block[idx-1] is >= key. We should go to that element.
itr.seekHelper(idx-1, key)
if itr.err == io.EOF {
// Case 1. Need to visit block[idx].
if idx == len(itr.t.blockIndex) {
// If idx == len(itr.t.blockIndex), then input key is greater than ANY element of table.
// There's nothing we can do. Valid() should return false as we seek to end of table.
return
}
// Since block[idx].smallest is > key. This is essentially a block[idx].SeekToFirst.
itr.seekHelper(idx, key)
}
// Case 2: No need to do anything. We already did the seek in block[idx-1].
}
// seek will reset iterator and seek to >= key.
func (itr *Iterator) seek(key []byte) {
itr.seekFrom(key, origin)
}
// seekForPrev will reset iterator and seek to <= key.
func (itr *Iterator) seekForPrev(key []byte) {
// TODO: Optimize this. We shouldn't have to take a Prev step.
itr.seekFrom(key, origin)
if !bytes.Equal(itr.Key(), key) {
itr.prev()
}
}
func (itr *Iterator) next() {
itr.err = nil
if itr.bpos >= len(itr.t.blockIndex) {
itr.err = io.EOF
return
}
if itr.bi == nil {
block, err := itr.t.block(itr.bpos)
if err != nil {
itr.err = err
return
}
itr.bi = block.NewIterator()
itr.bi.SeekToFirst()
itr.err = itr.bi.Error()
return
}
itr.bi.Next()
if !itr.bi.Valid() {
itr.bpos++
itr.bi = nil
itr.next()
return
}
}
func (itr *Iterator) prev() {
itr.err = nil
if itr.bpos < 0 {
itr.err = io.EOF
return
}
if itr.bi == nil {
block, err := itr.t.block(itr.bpos)
if err != nil {
itr.err = err
return
}
itr.bi = block.NewIterator()
itr.bi.SeekToLast()
itr.err = itr.bi.Error()
return
}
itr.bi.Prev()
if !itr.bi.Valid() {
itr.bpos--
itr.bi = nil
itr.prev()
return
}
}
// Key follows the y.Iterator interface.
// Returns the key with timestamp.
func (itr *Iterator) Key() []byte {
return itr.bi.Key()
}
// Value follows the y.Iterator interface
func (itr *Iterator) Value() (ret y.ValueStruct) {
ret.Decode(itr.bi.Value())
return
}
// Next follows the y.Iterator interface
func (itr *Iterator) Next() {
if !itr.reversed {
itr.next()
} else {
itr.prev()
}
}
// Rewind follows the y.Iterator interface
func (itr *Iterator) Rewind() {
if !itr.reversed {
itr.seekToFirst()
} else {
itr.seekToLast()
}
}
// Seek follows the y.Iterator interface
func (itr *Iterator) Seek(key []byte) {
if !itr.reversed {
itr.seek(key)
} else {
itr.seekForPrev(key)
}
}
// ConcatIterator concatenates the sequences defined by several iterators. (It only works with
// TableIterators, probably just because it's faster to not be so generic.)
type ConcatIterator struct {
idx int // Which iterator is active now.
cur *Iterator
iters []*Iterator // Corresponds to tables.
tables []*Table // Disregarding reversed, this is in ascending order.
reversed bool
}
// NewConcatIterator creates a new concatenated iterator
func NewConcatIterator(tbls []*Table, reversed bool) *ConcatIterator {
iters := make([]*Iterator, len(tbls))
for i := 0; i < len(tbls); i++ {
// Increment the reference count. Since, we're not creating the iterator right now.
// Here, We'll hold the reference of the tables, till the lifecycle of the iterator.
tbls[i].IncrRef()
// Save cycles by not initializing the iterators until needed.
// iters[i] = tbls[i].NewIterator(reversed)
}
return &ConcatIterator{
reversed: reversed,
iters: iters,
tables: tbls,
idx: -1, // Not really necessary because s.it.Valid()=false, but good to have.
}
}
func (s *ConcatIterator) setIdx(idx int) {
s.idx = idx
if idx < 0 || idx >= len(s.iters) {
s.cur = nil
return
}
if s.iters[idx] == nil {
s.iters[idx] = s.tables[idx].NewIterator(s.reversed)
}
s.cur = s.iters[s.idx]
}
// Rewind implements y.Interface
func (s *ConcatIterator) Rewind() {
if len(s.iters) == 0 {
return
}
if !s.reversed {
s.setIdx(0)
} else {
s.setIdx(len(s.iters) - 1)
}
s.cur.Rewind()
}
// Valid implements y.Interface
func (s *ConcatIterator) Valid() bool {
return s.cur != nil && s.cur.Valid()
}
// Key implements y.Interface
func (s *ConcatIterator) Key() []byte {
return s.cur.Key()
}
// Value implements y.Interface
func (s *ConcatIterator) Value() y.ValueStruct {
return s.cur.Value()
}
// Seek brings us to element >= key if reversed is false. Otherwise, <= key.
func (s *ConcatIterator) Seek(key []byte) {
var idx int
if !s.reversed {
idx = sort.Search(len(s.tables), func(i int) bool {
return y.CompareKeys(s.tables[i].Biggest(), key) >= 0
})
} else {
n := len(s.tables)
idx = n - 1 - sort.Search(n, func(i int) bool {
return y.CompareKeys(s.tables[n-1-i].Smallest(), key) <= 0
})
}
if idx >= len(s.tables) || idx < 0 {
s.setIdx(-1)
return
}
// For reversed=false, we know s.tables[i-1].Biggest() < key. Thus, the
// previous table cannot possibly contain key.
s.setIdx(idx)
s.cur.Seek(key)
}
// Next advances our concat iterator.
func (s *ConcatIterator) Next() {
s.cur.Next()
if s.cur.Valid() {
// Nothing to do. Just stay with the current table.
return
}
for { // In case there are empty tables.
if !s.reversed {
s.setIdx(s.idx + 1)
} else {
s.setIdx(s.idx - 1)
}
if s.cur == nil {
// End of list. Valid will become false.
return
}
s.cur.Rewind()
if s.cur.Valid() {
break
}
}
}
// Close implements y.Interface.
func (s *ConcatIterator) Close() error {
for _, t := range s.tables {
// DeReference the tables while closing the iterator.
if err := t.DecrRef(); err != nil {
return err
}
}
for _, it := range s.iters {
if it == nil {
continue
}
if err := it.Close(); err != nil {
return errors.Wrap(err, "ConcatIterator")
}
}
return nil
}