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143 Zeilen
3.1 KiB
143 Zeilen
3.1 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include "table/merger.h"
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#include "include/comparator.h"
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#include "include/iterator.h"
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#include "table/iterator_wrapper.h"
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namespace leveldb {
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namespace {
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class MergingIterator : public Iterator {
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public:
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MergingIterator(const Comparator* comparator, Iterator** children, int n)
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: comparator_(comparator),
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children_(new IteratorWrapper[n]),
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n_(n),
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current_(NULL) {
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for (int i = 0; i < n; i++) {
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children_[i].Set(children[i]);
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}
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}
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virtual ~MergingIterator() {
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delete[] children_;
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}
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virtual bool Valid() const {
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return (current_ != NULL);
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}
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virtual void SeekToFirst() {
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for (int i = 0; i < n_; i++) {
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children_[i].SeekToFirst();
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}
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FindSmallest();
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}
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virtual void SeekToLast() {
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for (int i = 0; i < n_; i++) {
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children_[i].SeekToLast();
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}
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FindLargest();
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}
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virtual void Seek(const Slice& target) {
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for (int i = 0; i < n_; i++) {
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children_[i].Seek(target);
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}
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FindSmallest();
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}
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virtual void Next() {
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assert(Valid());
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current_->Next();
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FindSmallest();
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}
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virtual void Prev() {
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assert(Valid());
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current_->Prev();
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FindLargest();
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}
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virtual Slice key() const {
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assert(Valid());
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return current_->key();
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}
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virtual Slice value() const {
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assert(Valid());
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return current_->value();
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}
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virtual Status status() const {
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Status status;
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for (int i = 0; i < n_; i++) {
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status = children_[i].status();
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if (!status.ok()) {
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break;
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}
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}
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return status;
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}
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private:
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void FindSmallest();
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void FindLargest();
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// We might want to use a heap in case there are lots of children.
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// For now we use a simple array since we expect a very small number
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// of children in leveldb.
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const Comparator* comparator_;
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IteratorWrapper* children_;
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int n_;
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IteratorWrapper* current_;
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};
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void MergingIterator::FindSmallest() {
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IteratorWrapper* smallest = NULL;
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for (int i = 0; i < n_; i++) {
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IteratorWrapper* child = &children_[i];
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if (child->Valid()) {
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if (smallest == NULL) {
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smallest = child;
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} else if (comparator_->Compare(child->key(), smallest->key()) < 0) {
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smallest = child;
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}
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}
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}
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current_ = smallest;
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}
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void MergingIterator::FindLargest() {
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IteratorWrapper* largest = NULL;
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for (int i = n_-1; i >= 0; i--) {
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IteratorWrapper* child = &children_[i];
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if (child->Valid()) {
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if (largest == NULL) {
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largest = child;
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} else if (comparator_->Compare(child->key(), largest->key()) > 0) {
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largest = child;
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}
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}
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}
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current_ = largest;
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}
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}
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Iterator* NewMergingIterator(const Comparator* cmp, Iterator** list, int n) {
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assert(n >= 0);
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if (n == 0) {
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return NewEmptyIterator();
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} else if (n == 1) {
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return list[0];
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} else {
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return new MergingIterator(cmp, list, n);
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}
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}
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}
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