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171 行
4.8 KiB
171 行
4.8 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/two_level_iterator.h"
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#include "leveldb/table.h"
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#include "table/block.h"
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#include "table/format.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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typedef Iterator* (*BlockFunction)(void*, const ReadOptions&, const Slice&);
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class TwoLevelIterator : public Iterator {
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public:
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TwoLevelIterator(Iterator* index_iter, BlockFunction block_function,
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void* arg, const ReadOptions& options);
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~TwoLevelIterator() override;
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void Seek(const Slice& target) override;
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void SeekToFirst() override;
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void SeekToLast() override;
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void Next() override;
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void Prev() override;
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bool Valid() const override { return data_iter_.Valid(); }
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Slice key() const override {
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assert(Valid());
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return data_iter_.key();
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}
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Slice value() const override {
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assert(Valid());
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return data_iter_.value();
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}
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Status status() const override {
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// It'd be nice if status() returned a const Status& instead of a Status
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if (!index_iter_.status().ok()) {
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return index_iter_.status();
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} else if (data_iter_.iter() != nullptr && !data_iter_.status().ok()) {
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return data_iter_.status();
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} else {
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return status_;
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}
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}
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private:
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void SaveError(const Status& s) {
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if (status_.ok() && !s.ok()) status_ = s;
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}
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void SkipEmptyDataBlocksForward();
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void SkipEmptyDataBlocksBackward();
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void SetDataIterator(Iterator* data_iter);
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void InitDataBlock();
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BlockFunction block_function_;
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void* arg_;
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const ReadOptions options_;
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Status status_;
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IteratorWrapper index_iter_;
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IteratorWrapper data_iter_; // May be nullptr
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// If data_iter_ is non-null, then "data_block_handle_" holds the
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// "index_value" passed to block_function_ to create the data_iter_.
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std::string data_block_handle_;
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};
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TwoLevelIterator::TwoLevelIterator(Iterator* index_iter,
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BlockFunction block_function, void* arg,
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const ReadOptions& options)
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: block_function_(block_function),
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arg_(arg),
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options_(options),
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index_iter_(index_iter),
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data_iter_(nullptr) {}
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TwoLevelIterator::~TwoLevelIterator() = default;
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void TwoLevelIterator::Seek(const Slice& target) {
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index_iter_.Seek(target);
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InitDataBlock();
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if (data_iter_.iter() != nullptr) data_iter_.Seek(target);
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SkipEmptyDataBlocksForward();
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}
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void TwoLevelIterator::SeekToFirst() {
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index_iter_.SeekToFirst();
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InitDataBlock();
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if (data_iter_.iter() != nullptr) data_iter_.SeekToFirst();
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SkipEmptyDataBlocksForward();
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}
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void TwoLevelIterator::SeekToLast() {
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index_iter_.SeekToLast();
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InitDataBlock();
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if (data_iter_.iter() != nullptr) data_iter_.SeekToLast();
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SkipEmptyDataBlocksBackward();
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}
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void TwoLevelIterator::Next() {
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assert(Valid());
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data_iter_.Next();
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SkipEmptyDataBlocksForward();
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}
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void TwoLevelIterator::Prev() {
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assert(Valid());
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data_iter_.Prev();
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SkipEmptyDataBlocksBackward();
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}
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void TwoLevelIterator::SkipEmptyDataBlocksForward() {
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while (data_iter_.iter() == nullptr || !data_iter_.Valid()) {
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// Move to next block
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if (!index_iter_.Valid()) {
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SetDataIterator(nullptr);
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return;
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}
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index_iter_.Next();
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InitDataBlock();
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if (data_iter_.iter() != nullptr) data_iter_.SeekToFirst();
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}
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}
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void TwoLevelIterator::SkipEmptyDataBlocksBackward() {
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while (data_iter_.iter() == nullptr || !data_iter_.Valid()) {
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// Move to next block
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if (!index_iter_.Valid()) {
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SetDataIterator(nullptr);
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return;
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}
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index_iter_.Prev();
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InitDataBlock();
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if (data_iter_.iter() != nullptr) data_iter_.SeekToLast();
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}
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}
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void TwoLevelIterator::SetDataIterator(Iterator* data_iter) {
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if (data_iter_.iter() != nullptr) SaveError(data_iter_.status());
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data_iter_.Set(data_iter);
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}
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void TwoLevelIterator::InitDataBlock() {
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if (!index_iter_.Valid()) {
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SetDataIterator(nullptr);
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} else {
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Slice handle = index_iter_.value();
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if (data_iter_.iter() != nullptr &&
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handle.compare(data_block_handle_) == 0) {
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// data_iter_ is already constructed with this iterator, so
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// no need to change anything
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} else {
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Iterator* iter = (*block_function_)(arg_, options_, handle);
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data_block_handle_.assign(handle.data(), handle.size());
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SetDataIterator(iter);
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}
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}
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}
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} // namespace
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Iterator* NewTwoLevelIterator(Iterator* index_iter,
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BlockFunction block_function, void* arg,
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const ReadOptions& options) {
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return new TwoLevelIterator(index_iter, block_function, arg, options);
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}
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} // namespace leveldb
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