ceremonyclient/pebble/internal/arenaskl/iterator.go

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2024-01-03 07:31:42 +00:00
/*
* Copyright 2017 Dgraph Labs, Inc. and Contributors
* Modifications copyright (C) 2017 Andy Kimball 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 arenaskl
import (
"context"
"sync"
"github.com/cockroachdb/pebble/internal/base"
)
type splice struct {
prev *node
next *node
}
func (s *splice) init(prev, next *node) {
s.prev = prev
s.next = next
}
// Iterator is an iterator over the skiplist object. Use Skiplist.NewIter
// to construct an iterator. The current state of the iterator can be cloned by
// simply value copying the struct. All iterator methods are thread-safe.
type Iterator struct {
list *Skiplist
nd *node
key base.InternalKey
lower []byte
upper []byte
}
// Iterator implements the base.InternalIterator interface.
var _ base.InternalIterator = (*Iterator)(nil)
var iterPool = sync.Pool{
New: func() interface{} {
return &Iterator{}
},
}
// Close resets the iterator.
func (it *Iterator) Close() error {
it.list = nil
it.nd = nil
it.lower = nil
it.upper = nil
iterPool.Put(it)
return nil
}
func (it *Iterator) String() string {
return "memtable"
}
// Error returns any accumulated error.
func (it *Iterator) Error() error {
return nil
}
// SeekGE moves the iterator to the first entry whose key is greater than or
// equal to the given key. Returns the key and value if the iterator is
// pointing at a valid entry, and (nil, nil) otherwise. Note that SeekGE only
// checks the upper bound. It is up to the caller to ensure that key is greater
// than or equal to the lower bound.
func (it *Iterator) SeekGE(key []byte, flags base.SeekGEFlags) (*base.InternalKey, base.LazyValue) {
if flags.TrySeekUsingNext() {
if it.nd == it.list.tail {
// Iterator is done.
return nil, base.LazyValue{}
}
less := it.list.cmp(it.key.UserKey, key) < 0
// Arbitrary constant. By measuring the seek cost as a function of the
// number of elements in the skip list, and fitting to a model, we
// could adjust the number of nexts based on the current size of the
// skip list.
const numNexts = 5
for i := 0; less && i < numNexts; i++ {
k, _ := it.Next()
if k == nil {
// Iterator is done.
return nil, base.LazyValue{}
}
less = it.list.cmp(it.key.UserKey, key) < 0
}
if !less {
return &it.key, base.MakeInPlaceValue(it.value())
}
}
_, it.nd, _ = it.seekForBaseSplice(key)
if it.nd == it.list.tail {
return nil, base.LazyValue{}
}
it.decodeKey()
if it.upper != nil && it.list.cmp(it.upper, it.key.UserKey) <= 0 {
it.nd = it.list.tail
return nil, base.LazyValue{}
}
return &it.key, base.MakeInPlaceValue(it.value())
}
// SeekPrefixGE moves the iterator to the first entry whose key is greater than
// or equal to the given key. This method is equivalent to SeekGE and is
// provided so that an arenaskl.Iterator implements the
// internal/base.InternalIterator interface.
func (it *Iterator) SeekPrefixGE(
prefix, key []byte, flags base.SeekGEFlags,
) (*base.InternalKey, base.LazyValue) {
return it.SeekGE(key, flags)
}
// SeekLT moves the iterator to the last entry whose key is less than the given
// key. Returns the key and value if the iterator is pointing at a valid entry,
// and (nil, nil) otherwise. Note that SeekLT only checks the lower bound. It
// is up to the caller to ensure that key is less than the upper bound.
func (it *Iterator) SeekLT(key []byte, flags base.SeekLTFlags) (*base.InternalKey, base.LazyValue) {
// NB: the top-level Iterator has already adjusted key based on
// the upper-bound.
it.nd, _, _ = it.seekForBaseSplice(key)
if it.nd == it.list.head {
return nil, base.LazyValue{}
}
it.decodeKey()
if it.lower != nil && it.list.cmp(it.lower, it.key.UserKey) > 0 {
it.nd = it.list.head
return nil, base.LazyValue{}
}
return &it.key, base.MakeInPlaceValue(it.value())
}
// First seeks position at the first entry in list. Returns the key and value
// if the iterator is pointing at a valid entry, and (nil, nil) otherwise. Note
// that First only checks the upper bound. It is up to the caller to ensure
// that key is greater than or equal to the lower bound (e.g. via a call to SeekGE(lower)).
func (it *Iterator) First() (*base.InternalKey, base.LazyValue) {
it.nd = it.list.getNext(it.list.head, 0)
if it.nd == it.list.tail {
return nil, base.LazyValue{}
}
it.decodeKey()
if it.upper != nil && it.list.cmp(it.upper, it.key.UserKey) <= 0 {
it.nd = it.list.tail
return nil, base.LazyValue{}
}
return &it.key, base.MakeInPlaceValue(it.value())
}
// Last seeks position at the last entry in list. Returns the key and value if
// the iterator is pointing at a valid entry, and (nil, nil) otherwise. Note
// that Last only checks the lower bound. It is up to the caller to ensure that
// key is less than the upper bound (e.g. via a call to SeekLT(upper)).
func (it *Iterator) Last() (*base.InternalKey, base.LazyValue) {
it.nd = it.list.getPrev(it.list.tail, 0)
if it.nd == it.list.head {
return nil, base.LazyValue{}
}
it.decodeKey()
if it.lower != nil && it.list.cmp(it.lower, it.key.UserKey) > 0 {
it.nd = it.list.head
return nil, base.LazyValue{}
}
return &it.key, base.MakeInPlaceValue(it.value())
}
// Next advances to the next position. Returns the key and value if the
// iterator is pointing at a valid entry, and (nil, nil) otherwise.
// Note: flushIterator.Next mirrors the implementation of Iterator.Next
// due to performance. Keep the two in sync.
func (it *Iterator) Next() (*base.InternalKey, base.LazyValue) {
it.nd = it.list.getNext(it.nd, 0)
if it.nd == it.list.tail {
return nil, base.LazyValue{}
}
it.decodeKey()
if it.upper != nil && it.list.cmp(it.upper, it.key.UserKey) <= 0 {
it.nd = it.list.tail
return nil, base.LazyValue{}
}
return &it.key, base.MakeInPlaceValue(it.value())
}
// NextPrefix advances to the next position with a new prefix. Returns the key
// and value if the iterator is pointing at a valid entry, and (nil, nil)
// otherwise.
func (it *Iterator) NextPrefix(succKey []byte) (*base.InternalKey, base.LazyValue) {
return it.SeekGE(succKey, base.SeekGEFlagsNone.EnableTrySeekUsingNext())
}
// Prev moves to the previous position. Returns the key and value if the
// iterator is pointing at a valid entry, and (nil, nil) otherwise.
func (it *Iterator) Prev() (*base.InternalKey, base.LazyValue) {
it.nd = it.list.getPrev(it.nd, 0)
if it.nd == it.list.head {
return nil, base.LazyValue{}
}
it.decodeKey()
if it.lower != nil && it.list.cmp(it.lower, it.key.UserKey) > 0 {
it.nd = it.list.head
return nil, base.LazyValue{}
}
return &it.key, base.MakeInPlaceValue(it.value())
}
// value returns the value at the current position.
func (it *Iterator) value() []byte {
return it.nd.getValue(it.list.arena)
}
// Head true iff the iterator is positioned at the sentinel head node.
func (it *Iterator) Head() bool {
return it.nd == it.list.head
}
// Tail true iff the iterator is positioned at the sentinel tail node.
func (it *Iterator) Tail() bool {
return it.nd == it.list.tail
}
// SetBounds sets the lower and upper bounds for the iterator. Note that the
// result of Next and Prev will be undefined until the iterator has been
// repositioned with SeekGE, SeekPrefixGE, SeekLT, First, or Last.
func (it *Iterator) SetBounds(lower, upper []byte) {
it.lower = lower
it.upper = upper
}
// SetContext implements base.InternalIterator.
func (it *Iterator) SetContext(_ context.Context) {}
func (it *Iterator) decodeKey() {
it.key.UserKey = it.list.arena.getBytes(it.nd.keyOffset, it.nd.keySize)
it.key.Trailer = it.nd.keyTrailer
}
func (it *Iterator) seekForBaseSplice(key []byte) (prev, next *node, found bool) {
ikey := base.MakeSearchKey(key)
level := int(it.list.Height() - 1)
prev = it.list.head
for {
prev, next, found = it.list.findSpliceForLevel(ikey, level, prev)
if found {
if level != 0 {
// next is pointing at the target node, but we need to find previous on
// the bottom level.
prev = it.list.getPrev(next, 0)
}
break
}
if level == 0 {
break
}
level--
}
return
}