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			224 lines
		
	
	
		
			6.5 KiB
		
	
	
	
		
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			224 lines
		
	
	
		
			6.5 KiB
		
	
	
	
		
			Go
		
	
	
	
	
	
/*
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 * Copyright 2017 Dgraph Labs, Inc. and Contributors
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 * Modifications copyright (C) 2017 Andy Kimball and Contributors
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 *
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 * Licensed under the Apache License, Version 2.0 (the "License");
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 * you may not use this file except in compliance with the License.
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 * You may obtain a copy of the License at
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 *
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 *     http://www.apache.org/licenses/LICENSE-2.0
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 *
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 * Unless required by applicable law or agreed to in writing, software
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 * distributed under the License is distributed on an "AS IS" BASIS,
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 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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 * See the License for the specific language governing permissions and
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 * limitations under the License.
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 */
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package batchskl
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import "github.com/cockroachdb/pebble/internal/base"
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type splice struct {
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	prev uint32
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	next uint32
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}
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// Iterator is an iterator over the skiplist object. Use Skiplist.NewIter
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// to construct an iterator. The current state of the iterator can be cloned
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// by simply value copying the struct.
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type Iterator struct {
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	list  *Skiplist
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	nd    uint32
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	key   base.InternalKey
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	lower []byte
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	upper []byte
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}
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// Close resets the iterator.
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func (it *Iterator) Close() error {
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	it.list = nil
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	it.nd = 0
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	return nil
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}
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// SeekGE moves the iterator to the first entry whose key is greater than or
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// equal to the given key. Returns true if the iterator is pointing at a valid
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// entry and false otherwise. Note that SeekGE only checks the upper bound. It
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// is up to the caller to ensure that key is greater than or equal to the lower
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// bound.
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func (it *Iterator) SeekGE(key []byte, flags base.SeekGEFlags) *base.InternalKey {
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	if flags.TrySeekUsingNext() {
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		if it.nd == it.list.tail {
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			// Iterator is done.
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			return nil
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		}
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		less := it.list.cmp(it.key.UserKey, key) < 0
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		// Arbitrary constant. By measuring the seek cost as a function of the
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		// number of elements in the skip list, and fitting to a model, we
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		// could adjust the number of nexts based on the current size of the
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		// skip list.
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		const numNexts = 5
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		for i := 0; less && i < numNexts; i++ {
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			k := it.Next()
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			if k == nil {
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				// Iterator is done.
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				return nil
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			}
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			less = it.list.cmp(k.UserKey, key) < 0
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		}
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		if !less {
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			return &it.key
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		}
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	}
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	_, it.nd = it.seekForBaseSplice(key, it.list.abbreviatedKey(key))
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	if it.nd == it.list.tail {
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		return nil
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	}
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	nodeKey := it.list.getKey(it.nd)
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	if it.upper != nil && it.list.cmp(it.upper, nodeKey.UserKey) <= 0 {
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		it.nd = it.list.tail
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		return nil
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	}
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	it.key = nodeKey
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	return &it.key
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}
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// SeekLT moves the iterator to the last entry whose key is less the given
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// key. Returns true if the iterator is pointing at a valid entry and false
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// otherwise. Note that SeekLT only checks the lower bound. It is up to the
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// caller to ensure that key is less than the upper bound.
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func (it *Iterator) SeekLT(key []byte) *base.InternalKey {
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	it.nd, _ = it.seekForBaseSplice(key, it.list.abbreviatedKey(key))
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	if it.nd == it.list.head {
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		return nil
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	}
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	nodeKey := it.list.getKey(it.nd)
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	if it.lower != nil && it.list.cmp(it.lower, nodeKey.UserKey) > 0 {
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		it.nd = it.list.head
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		return nil
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	}
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	it.key = nodeKey
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	return &it.key
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}
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// First seeks position at the first entry in list. Final state of iterator is
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// Valid() iff list is not empty. Note that First only checks the upper
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// bound. It is up to the caller to ensure that key is greater than or equal to
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// the lower bound (e.g. via a call to SeekGE(lower)).
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func (it *Iterator) First() *base.InternalKey {
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	it.nd = it.list.getNext(it.list.head, 0)
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	if it.nd == it.list.tail {
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		return nil
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	}
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	nodeKey := it.list.getKey(it.nd)
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	if it.upper != nil && it.list.cmp(it.upper, nodeKey.UserKey) <= 0 {
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		it.nd = it.list.tail
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		return nil
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	}
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	it.key = nodeKey
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	return &it.key
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}
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// Last seeks position at the last entry in list. Final state of iterator is
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// Valid() iff list is not empty. Note that Last only checks the lower
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// bound. It is up to the caller to ensure that key is less than the upper
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// bound (e.g. via a call to SeekLT(upper)).
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func (it *Iterator) Last() *base.InternalKey {
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	it.nd = it.list.getPrev(it.list.tail, 0)
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	if it.nd == it.list.head {
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		return nil
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	}
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	nodeKey := it.list.getKey(it.nd)
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	if it.lower != nil && it.list.cmp(it.lower, nodeKey.UserKey) > 0 {
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		it.nd = it.list.head
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		return nil
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	}
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	it.key = nodeKey
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	return &it.key
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}
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// Next advances to the next position. If there are no following nodes, then
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// Valid() will be false after this call.
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func (it *Iterator) Next() *base.InternalKey {
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	it.nd = it.list.getNext(it.nd, 0)
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	if it.nd == it.list.tail {
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		return nil
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	}
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	nodeKey := it.list.getKey(it.nd)
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	if it.upper != nil && it.list.cmp(it.upper, nodeKey.UserKey) <= 0 {
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		it.nd = it.list.tail
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		return nil
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	}
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	it.key = nodeKey
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	return &it.key
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}
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// Prev moves to the previous position. If there are no previous nodes, then
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// Valid() will be false after this call.
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func (it *Iterator) Prev() *base.InternalKey {
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	it.nd = it.list.getPrev(it.nd, 0)
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	if it.nd == it.list.head {
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		return nil
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	}
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	nodeKey := it.list.getKey(it.nd)
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	if it.lower != nil && it.list.cmp(it.lower, nodeKey.UserKey) > 0 {
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		it.nd = it.list.head
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		return nil
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	}
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	it.key = nodeKey
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	return &it.key
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}
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// Key returns the key at the current position.
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func (it *Iterator) Key() *base.InternalKey {
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	return &it.key
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}
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// KeyInfo returns the offset of the start of the record, the start of the key,
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// and the end of the key.
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func (it *Iterator) KeyInfo() (offset, keyStart, keyEnd uint32) {
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	n := it.list.node(it.nd)
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	return n.offset, n.keyStart, n.keyEnd
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}
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// Head true iff the iterator is positioned at the sentinel head node.
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func (it *Iterator) Head() bool {
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	return it.nd == it.list.head
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}
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// Tail true iff the iterator is positioned at the sentinel tail node.
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func (it *Iterator) Tail() bool {
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	return it.nd == it.list.tail
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}
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// Valid returns nil iff the iterator is positioned at a valid node.
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func (it *Iterator) Valid() bool {
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	return it.list != nil && it.nd != it.list.head && it.nd != it.list.tail
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}
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func (it *Iterator) String() string {
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	return "batch"
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}
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// SetBounds sets the lower and upper bounds for the iterator. Note that the
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// result of Next and Prev will be undefined until the iterator has been
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// repositioned with SeekGE, SeekLT, First, or Last.
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func (it *Iterator) SetBounds(lower, upper []byte) {
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	it.lower = lower
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	it.upper = upper
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}
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func (it *Iterator) seekForBaseSplice(key []byte, abbreviatedKey uint64) (prev, next uint32) {
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	prev = it.list.head
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	for level := it.list.height - 1; ; level-- {
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		prev, next = it.list.findSpliceForLevel(key, abbreviatedKey, level, prev)
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		if level == 0 {
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			break
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		}
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	}
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	return
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}
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