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243 lines
7.0 KiB
243 lines
7.0 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 <iostream>
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#include <fstream>
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#include <thread>
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#include "db/prefetch_iter.h"
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#include "db/db_impl.h"
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#include "db/dbformat.h"
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#include "db/filename.h"
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#include "leveldb/env.h"
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#include "leveldb/iterator.h"
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#include "port/port.h"
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#include "util/logging.h"
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#include "util/mutexlock.h"
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#include "util/random.h"
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#include "port/port.h"
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namespace leveldb {
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namespace {
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// Memtables and sstables that make the DB representation contain
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// (userkey,seq,type) => uservalue entries. DBPreFetchIter
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// combines multiple entries for the same userkey found in the DB
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// representation into a single entry while accounting for sequence
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// numbers, deletion markers, overwrites, etc.
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class DBPreFetchIter : public Iterator {
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public:
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// Which direction is the iterator currently moving?
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// (1) When moving forward, the internal iterator is positioned at
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// the exact entry that yields this->key(), this->value()
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// (2) When moving backwards, the internal iterator is positioned
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// just before all entries whose user key == this->key().
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enum IterPos {Left,Mid,Right};
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DBPreFetchIter(DBImpl* db, Iterator* iter, std::vector<Iterator*> prefetch_iters,int prefetch_num)
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:
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db_(db),iter_(iter),prefetch_iters_(prefetch_iters),prefetch_num_(prefetch_num) {}
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DBPreFetchIter(const DBPreFetchIter&) = delete;
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DBPreFetchIter& operator=(const DBPreFetchIter&) = delete;
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~DBPreFetchIter() override {
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if(prefetch_thread.joinable()){
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stop_flag.store(true);
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prefetch_thread.join();
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for(auto iter:prefetch_iters_){
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delete iter;
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}
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}
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std::cout<<"fetch:"<<fetched_<<" unfetch:"<<unfetched_<<"\n";
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delete iter_;
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}
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bool Valid() const override { return iter_->Valid(); }
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Slice key() const override {
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return iter_->key();
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}
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Slice value() const override {
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if(cur_pos>0&&cur_pos<1000000&&prefetched_array[cur_pos].load()){
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fetched_++;
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return prefetch_array[cur_pos];
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}
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else{
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unfetched_++;
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return GetAndParseTrueValue(iter_);
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}
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}
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Status status() const override {
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return iter_->status();
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}
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void Next() override;
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void Prev() 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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private:
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Slice GetAndParseTrueValue(Iterator* iter)const{
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Slice tmp_value=iter->value();
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Slice key;
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if(tmp_value.size()==0)return tmp_value;
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if(tmp_value.data()[0]==0x00){
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tmp_value.remove_prefix(1);
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return tmp_value;
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}
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tmp_value.remove_prefix(1);
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uint64_t file_id,valuelog_offset,valuelog_len;
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bool res=GetVarint64(&tmp_value,&file_id);
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if(!res)assert(0);
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res=GetVarint64(&tmp_value,&valuelog_offset);
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if(!res)assert(0);
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db_->ReadValueLog(file_id,valuelog_offset, &key, &tmp_value);
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return tmp_value;
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}
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void PreFetchThreadForward(){
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std::thread prefetch_threads[prefetch_num_];
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for(int i=0;i<prefetch_num_;i++){
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Iterator* prefetch_iter_=prefetch_iters_[i];
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int skip_num=i;
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prefetch_threads[i]=std::thread([this,prefetch_iter_,skip_num]() {
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int pos=skip_num;
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for(int j=0;j<skip_num;j++){
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if(prefetch_iter_->Valid())prefetch_iter_->Next();
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}
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while(prefetch_iter_->Valid()){
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Slice key_=prefetch_iter_->key();
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std::string str_key=std::string(key_.data(),key_.size());
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Slice val=GetAndParseTrueValue(prefetch_iter_);
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prefetch_array[pos]=val;
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prefetched_array[pos].store(true);
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if(stop_flag.load()||pos>1000000){
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break;
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}
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for(int j=0;j<prefetch_num_;j++){
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if(prefetch_iter_->Valid())prefetch_iter_->Next();
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}
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pos+=prefetch_num_+1;
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}
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});
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}
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for (auto& thread : prefetch_threads) {
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if (thread.joinable()) {
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thread.join();
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}
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}
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}
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void PreFetchThreadBackward(){
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std::thread prefetch_threads[prefetch_num_];
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for(int i=0;i<prefetch_num_;i++){
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Iterator* prefetch_iter_=prefetch_iters_[i];
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int skip_num=i;
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prefetch_threads[i]=std::thread([this,prefetch_iter_,skip_num]() {
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int pos=1000000-skip_num;
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for(int j=0;j<skip_num;j++){
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if(prefetch_iter_->Valid())prefetch_iter_->Prev();
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}
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while(prefetch_iter_->Valid()){
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Slice key_=prefetch_iter_->key();
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std::string str_key=std::string(key_.data(),key_.size());
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Slice val=GetAndParseTrueValue(prefetch_iter_);
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if(stop_flag.load()||pos<0){
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break;
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}
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prefetch_array[pos]=val;
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prefetched_array[pos].store(true);
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for(int j=0;j<prefetch_num_;j++){
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if(prefetch_iter_->Valid())prefetch_iter_->Prev();
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}
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pos-=prefetch_num_+1;
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}
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});
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}
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for (auto& thread : prefetch_threads) {
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if (thread.joinable()) {
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thread.join();
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}
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}
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}
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DBImpl* db_;
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Iterator* const iter_;
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std::vector<Iterator*> const prefetch_iters_;
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int prefetch_num_;
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IterPos iter_pos_;
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std::atomic<bool> stop_flag;
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Slice prefetch_array[1000005];
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std::atomic<bool> prefetched_array[1000005];
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std::thread prefetch_thread;
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int cur_pos=0;
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mutable int fetched_=0;
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mutable int unfetched_=0;
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};
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void DBPreFetchIter::Next() {
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iter_->Next();cur_pos++;
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}
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void DBPreFetchIter::Prev() {
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iter_->Prev();cur_pos--;
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}
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void DBPreFetchIter::Seek(const Slice& target) {
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iter_->Seek(target);
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cur_pos=0;
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for(auto prefetch_iter_:prefetch_iters_)
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prefetch_iter_->Seek(target);
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if(prefetch_thread.joinable()){
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stop_flag.store(true);
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prefetch_thread.join();
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for(int i=0;i<1000000;i++)prefetched_array[i]=false;
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stop_flag=false;
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}
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prefetch_thread=std::thread([this]() {
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PreFetchThreadForward();
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});
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}
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void DBPreFetchIter::SeekToFirst() {
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iter_->SeekToFirst();
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cur_pos=0;
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for(auto prefetch_iter_:prefetch_iters_)
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prefetch_iter_->SeekToFirst();
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if(prefetch_thread.joinable()){
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stop_flag.store(true);
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prefetch_thread.join();
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for(int i=0;i<1000000;i++)prefetched_array[i]=false;
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stop_flag=false;
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}
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prefetch_thread=std::thread([this]() {
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PreFetchThreadForward();
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});
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}
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void DBPreFetchIter::SeekToLast() {
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iter_->SeekToLast();
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cur_pos=1000000;
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for(auto prefetch_iter_:prefetch_iters_)
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prefetch_iter_->SeekToLast();
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if(prefetch_thread.joinable()){
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stop_flag.store(true);
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prefetch_thread.join();
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for(int i=0;i<1000000;i++)prefetched_array[i]=false;
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stop_flag=false;
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}
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prefetch_thread=std::thread([this]() {
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PreFetchThreadBackward();
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});
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}
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} // anonymous namespace
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Iterator* NewPreFetchIterator(DBImpl* db,Iterator* db_iter,std::vector<Iterator*> prefetch_iters,int prefetch_num) {
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return new DBPreFetchIter(db,db_iter,prefetch_iters,prefetch_num);
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}
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} // namespace leveldb
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