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318 rindas
8.8 KiB
318 rindas
8.8 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 "db/db_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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namespace leveldb {
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#if 0
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static void DumpInternalIter(Iterator* iter) {
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for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
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ParsedInternalKey k;
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if (!ParseInternalKey(iter->key(), &k)) {
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std::fprintf(stderr, "Corrupt '%s'\n", EscapeString(iter->key()).c_str());
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} else {
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std::fprintf(stderr, "@ '%s'\n", k.DebugString().c_str());
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}
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}
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}
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#endif
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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. DBIter
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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 DBIter : 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 Direction { kForward, kReverse };
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DBIter(DBImpl* db, const Comparator* cmp, Iterator* iter, SequenceNumber s,
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uint32_t seed)
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: db_(db),
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user_comparator_(cmp),
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iter_(iter),
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sequence_(s),
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direction_(kForward),
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valid_(false),
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rnd_(seed),
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bytes_until_read_sampling_(RandomCompactionPeriod()) {}
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DBIter(const DBIter&) = delete;
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DBIter& operator=(const DBIter&) = delete;
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~DBIter() override { delete iter_; }
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bool Valid() const override { return valid_; }
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Slice key() const override {
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assert(valid_);
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return (direction_ == kForward) ? ExtractUserKey(iter_->key()) : saved_key_;
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}
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Slice value() const override {
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assert(valid_);
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return (direction_ == kForward) ? iter_->value() : saved_value_;
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}
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Status status() const override {
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if (status_.ok()) {
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return 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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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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void FindNextUserEntry(bool skipping, std::string* skip);
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void FindPrevUserEntry();
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bool ParseKey(ParsedInternalKey* key);
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inline void SaveKey(const Slice& k, std::string* dst) {
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dst->assign(k.data(), k.size());
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}
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inline void ClearSavedValue() {
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if (saved_value_.capacity() > 1048576) {
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std::string empty;
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swap(empty, saved_value_);
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} else {
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saved_value_.clear();
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}
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}
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// Picks the number of bytes that can be read until a compaction is scheduled.
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size_t RandomCompactionPeriod() {
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return rnd_.Uniform(2 * config::kReadBytesPeriod);
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}
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DBImpl* db_;
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const Comparator* const user_comparator_;
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Iterator* const iter_;
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SequenceNumber const sequence_;
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Status status_;
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std::string saved_key_; // == current key when direction_==kReverse
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std::string saved_value_; // == current raw value when direction_==kReverse
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Direction direction_;
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bool valid_;
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Random rnd_;
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size_t bytes_until_read_sampling_;
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};
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inline bool DBIter::ParseKey(ParsedInternalKey* ikey) {
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Slice k = iter_->key();
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size_t bytes_read = k.size() + iter_->value().size();
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while (bytes_until_read_sampling_ < bytes_read) {
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bytes_until_read_sampling_ += RandomCompactionPeriod();
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db_->RecordReadSample(k);
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}
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assert(bytes_until_read_sampling_ >= bytes_read);
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bytes_until_read_sampling_ -= bytes_read;
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if (!ParseInternalKey(k, ikey)) {
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status_ = Status::Corruption("corrupted internal key in DBIter");
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return false;
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} else {
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return true;
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}
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}
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void DBIter::Next() {
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assert(valid_);
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if (direction_ == kReverse) { // Switch directions?
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direction_ = kForward;
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// iter_ is pointing just before the entries for this->key(),
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// so advance into the range of entries for this->key() and then
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// use the normal skipping code below.
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if (!iter_->Valid()) {
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iter_->SeekToFirst();
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} else {
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iter_->Next();
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}
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if (!iter_->Valid()) {
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valid_ = false;
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saved_key_.clear();
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return;
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}
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// saved_key_ already contains the key to skip past.
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} else {
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// Store in saved_key_ the current key so we skip it below.
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SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
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// iter_ is pointing to current key. We can now safely move to the next to
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// avoid checking current key.
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iter_->Next();
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if (!iter_->Valid()) {
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valid_ = false;
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saved_key_.clear();
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return;
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}
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}
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FindNextUserEntry(true, &saved_key_);
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}
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void DBIter::FindNextUserEntry(bool skipping, std::string* skip) {
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// Loop until we hit an acceptable entry to yield
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assert(iter_->Valid());
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assert(direction_ == kForward);
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do {
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ParsedInternalKey ikey;
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if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
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switch (ikey.type) {
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case kTypeDeletion:
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// Arrange to skip all upcoming entries for this key since
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// they are hidden by this deletion.
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SaveKey(ikey.user_key, skip);
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skipping = true;
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break;
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case kTypeValue:
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if (skipping &&
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user_comparator_->Compare(ikey.user_key, *skip) <= 0) {
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// Entry hidden
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} else {
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valid_ = true;
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saved_key_.clear();
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return;
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}
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break;
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}
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}
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iter_->Next();
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} while (iter_->Valid());
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saved_key_.clear();
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valid_ = false;
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}
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void DBIter::Prev() {
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assert(valid_);
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if (direction_ == kForward) { // Switch directions?
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// iter_ is pointing at the current entry. Scan backwards until
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// the key changes so we can use the normal reverse scanning code.
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assert(iter_->Valid()); // Otherwise valid_ would have been false
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SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
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while (true) {
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iter_->Prev();
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if (!iter_->Valid()) {
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valid_ = false;
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saved_key_.clear();
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ClearSavedValue();
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return;
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}
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if (user_comparator_->Compare(ExtractUserKey(iter_->key()), saved_key_) <
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0) {
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break;
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}
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}
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direction_ = kReverse;
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}
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FindPrevUserEntry();
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}
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void DBIter::FindPrevUserEntry() {
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assert(direction_ == kReverse);
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ValueType value_type = kTypeDeletion;
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if (iter_->Valid()) {
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do {
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ParsedInternalKey ikey;
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if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
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if ((value_type != kTypeDeletion) &&
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user_comparator_->Compare(ikey.user_key, saved_key_) < 0) {
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// We encountered a non-deleted value in entries for previous keys,
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break;
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}
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value_type = ikey.type;
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if (value_type == kTypeDeletion) {
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saved_key_.clear();
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ClearSavedValue();
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} else {
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Slice raw_value = iter_->value();
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if (saved_value_.capacity() > raw_value.size() + 1048576) {
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std::string empty;
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swap(empty, saved_value_);
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}
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SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
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saved_value_.assign(raw_value.data(), raw_value.size());
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}
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}
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iter_->Prev();
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} while (iter_->Valid());
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}
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if (value_type == kTypeDeletion) {
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// End
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valid_ = false;
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saved_key_.clear();
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ClearSavedValue();
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direction_ = kForward;
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} else {
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valid_ = true;
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}
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}
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void DBIter::Seek(const Slice& target) {
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direction_ = kForward;
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ClearSavedValue();
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saved_key_.clear();
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AppendInternalKey(&saved_key_,
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ParsedInternalKey(target, sequence_, kValueTypeForSeek));
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iter_->Seek(saved_key_);
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if (iter_->Valid()) {
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FindNextUserEntry(false, &saved_key_ /* temporary storage */);
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} else {
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valid_ = false;
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}
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}
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void DBIter::SeekToFirst() {
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direction_ = kForward;
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ClearSavedValue();
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iter_->SeekToFirst();
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if (iter_->Valid()) {
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FindNextUserEntry(false, &saved_key_ /* temporary storage */);
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} else {
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valid_ = false;
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}
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}
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void DBIter::SeekToLast() {
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direction_ = kReverse;
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ClearSavedValue();
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iter_->SeekToLast();
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FindPrevUserEntry();
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}
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} // anonymous namespace
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Iterator* NewDBIterator(DBImpl* db, const Comparator* user_key_comparator,
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Iterator* internal_iter, SequenceNumber sequence,
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uint32_t seed) {
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return new DBIter(db, user_key_comparator, internal_iter, sequence, seed);
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}
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} // namespace leveldb
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