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397 lines
11 KiB
397 lines
11 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/filename.h"
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#include "db/dbformat.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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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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fprintf(stderr, "Corrupt '%s'\n", EscapeString(iter->key()).c_str());
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} else {
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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 {
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kForward,
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kReverse
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};
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DBIter(const std::string* dbname, Env* env,
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const Comparator* cmp, Iterator* iter, SequenceNumber s)
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: dbname_(dbname),
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env_(env),
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user_comparator_(cmp),
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iter_(iter),
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sequence_(s),
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large_(NULL),
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direction_(kForward),
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valid_(false) {
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}
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virtual ~DBIter() {
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delete iter_;
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delete large_;
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}
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virtual bool Valid() const { return valid_; }
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virtual Slice key() const {
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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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virtual Slice value() const {
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assert(valid_);
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Slice raw_value = (direction_ == kForward) ? iter_->value() : saved_value_;
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if (large_ == NULL) {
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return raw_value;
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} else {
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MutexLock l(&large_->mutex);
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if (!large_->produced) {
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ReadIndirectValue(raw_value);
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}
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return large_->value;
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}
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}
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virtual Status status() const {
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if (status_.ok()) {
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if (large_ != NULL && !large_->status.ok()) return large_->status;
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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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virtual void Next();
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virtual void Prev();
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virtual void Seek(const Slice& target);
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virtual void SeekToFirst();
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virtual void SeekToLast();
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private:
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struct Large {
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port::Mutex mutex;
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std::string value;
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bool produced;
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Status status;
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};
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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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void ReadIndirectValue(Slice ref) const;
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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 ForgetLargeValue() {
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if (large_ != NULL) {
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delete large_;
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large_ = NULL;
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}
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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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const std::string* const dbname_;
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Env* const env_;
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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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Large* large_; // Non-NULL if value is an indirect reference
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Direction direction_;
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bool valid_;
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// No copying allowed
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DBIter(const DBIter&);
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void operator=(const DBIter&);
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};
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inline bool DBIter::ParseKey(ParsedInternalKey* ikey) {
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if (!ParseInternalKey(iter_->key(), 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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ForgetLargeValue();
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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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}
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// Temporarily use saved_key_ as storage for key to skip.
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std::string* skip = &saved_key_;
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SaveKey(ExtractUserKey(iter_->key()), skip);
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FindNextUserEntry(true, skip);
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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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assert(large_ == NULL);
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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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case kTypeLargeValueRef:
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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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if (ikey.type == kTypeLargeValueRef) {
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large_ = new Large;
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large_->produced = false;
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}
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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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ForgetLargeValue();
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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()),
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saved_key_) < 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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assert(large_ == NULL);
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ValueType value_type = kTypeDeletion;
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if (iter_->Valid()) {
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SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
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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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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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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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if (value_type == kTypeLargeValueRef) {
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large_ = new Large;
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large_->produced = false;
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}
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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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ForgetLargeValue();
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ClearSavedValue();
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saved_key_.clear();
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AppendInternalKey(
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&saved_key_, 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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ForgetLargeValue();
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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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ForgetLargeValue();
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ClearSavedValue();
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iter_->SeekToLast();
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FindPrevUserEntry();
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}
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void DBIter::ReadIndirectValue(Slice ref) const {
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assert(!large_->produced);
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large_->produced = true;
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LargeValueRef large_ref;
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if (ref.size() != LargeValueRef::ByteSize()) {
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large_->status = Status::Corruption("malformed large value reference");
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return;
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}
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memcpy(large_ref.data, ref.data(), LargeValueRef::ByteSize());
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std::string fname = LargeValueFileName(*dbname_, large_ref);
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RandomAccessFile* file;
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Status s = env_->NewRandomAccessFile(fname, &file);
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uint64_t file_size = 0;
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if (s.ok()) {
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s = env_->GetFileSize(fname, &file_size);
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}
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if (s.ok()) {
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uint64_t value_size = large_ref.ValueSize();
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large_->value.resize(value_size);
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Slice result;
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s = file->Read(0, file_size, &result,
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const_cast<char*>(large_->value.data()));
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if (s.ok()) {
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if (result.size() == file_size) {
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switch (large_ref.compression_type()) {
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case kNoCompression: {
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if (result.data() != large_->value.data()) {
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large_->value.assign(result.data(), result.size());
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}
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break;
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}
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case kSnappyCompression: {
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std::string uncompressed;
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if (port::Snappy_Uncompress(result.data(), result.size(),
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&uncompressed) &&
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uncompressed.size() == large_ref.ValueSize()) {
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swap(uncompressed, large_->value);
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} else {
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s = Status::Corruption(
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"Unable to read entire compressed large value file");
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}
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}
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}
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} else {
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s = Status::Corruption("Unable to read entire large value file");
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}
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}
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delete file; // Ignore errors on closing
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}
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if (!s.ok()) {
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large_->value.clear();
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large_->status = s;
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}
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}
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} // anonymous namespace
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Iterator* NewDBIterator(
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const std::string* dbname,
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Env* env,
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const Comparator* user_key_comparator,
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Iterator* internal_iter,
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const SequenceNumber& sequence) {
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return new DBIter(dbname, env, user_key_comparator, internal_iter, sequence);
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}
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}
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