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412 righe
11 KiB
412 righe
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 "include/env.h"
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#include "include/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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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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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 key_;
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}
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virtual Slice value() const {
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assert(valid_);
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if (large_ == NULL) {
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return 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();
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}
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return large_->value;
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}
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}
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virtual void Next() {
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assert(valid_);
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// iter_ is already positioned past DBIter::key()
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FindNextUserEntry();
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}
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virtual void Prev() {
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assert(valid_);
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bool ignored;
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ScanUntilBeforeCurrentKey(&ignored);
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FindPrevUserEntry();
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}
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virtual void Seek(const Slice& target) {
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ParsedInternalKey ikey(target, sequence_, kValueTypeForSeek);
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std::string tmp;
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AppendInternalKey(&tmp, ikey);
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iter_->Seek(tmp);
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FindNextUserEntry();
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}
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virtual void SeekToFirst() {
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iter_->SeekToFirst();
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FindNextUserEntry();
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}
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virtual void SeekToLast();
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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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private:
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void FindNextUserEntry();
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void FindPrevUserEntry();
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void SaveKey(const Slice& k) { key_.assign(k.data(), k.size()); }
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void SaveValue(const Slice& v) {
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if (value_.capacity() > v.size() + 1048576) {
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std::string empty;
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swap(empty, value_);
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}
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value_.assign(v.data(), v.size());
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}
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bool ParseKey(ParsedInternalKey* key);
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void SkipPast(const Slice& k);
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void ScanUntilBeforeCurrentKey(bool* found_live);
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void ReadIndirectValue() const;
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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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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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// iter_ is positioned just past current entry for DBIter if valid_
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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 key_; // Always a user key
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std::string value_;
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Large* large_; // Non-NULL if value is an indirect reference
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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::FindNextUserEntry() {
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if (large_ != NULL) {
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if (status_.ok() && !large_->status.ok()) {
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status_ = large_->status;
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}
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delete large_;
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large_ = NULL;
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}
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while (iter_->Valid()) {
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ParsedInternalKey ikey;
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if (!ParseKey(&ikey)) {
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// Skip past corrupted entry
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iter_->Next();
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continue;
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}
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if (ikey.sequence > sequence_) {
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// Ignore entries newer than the snapshot
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iter_->Next();
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continue;
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}
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switch (ikey.type) {
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case kTypeDeletion:
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SaveKey(ikey.user_key); // Make local copy for use by SkipPast()
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iter_->Next();
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SkipPast(key_);
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// Do not return deleted entries. Instead keep looping.
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break;
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case kTypeValue:
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SaveKey(ikey.user_key);
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SaveValue(iter_->value());
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iter_->Next();
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SkipPast(key_);
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// Yield the value we just found.
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valid_ = true;
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return;
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case kTypeLargeValueRef:
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SaveKey(ikey.user_key);
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// Save the large value ref as value_, and read it lazily on a call
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// to value()
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SaveValue(iter_->value());
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large_ = new Large;
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large_->produced = false;
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iter_->Next();
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SkipPast(key_);
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// Yield the value we just found.
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valid_ = true;
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return;
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}
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}
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valid_ = false;
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key_.clear();
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value_.clear();
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assert(large_ == NULL);
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}
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void DBIter::SkipPast(const Slice& k) {
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while (iter_->Valid()) {
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ParsedInternalKey ikey;
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// Note that if we cannot parse an internal key, we keep looping
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// so that if we have a run like the following:
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// <x,100,v> => value100
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// <corrupted entry for user key x>
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// <x,50,v> => value50
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// we will skip over the corrupted entry as well as value50.
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if (ParseKey(&ikey) && user_comparator_->Compare(ikey.user_key, k) != 0) {
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break;
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}
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iter_->Next();
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}
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}
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void DBIter::SeekToLast() {
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// Position iter_ at the last uncorrupted user key and then
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// let FindPrevUserEntry() do the heavy lifting to find
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// a user key that is live.
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iter_->SeekToLast();
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ParsedInternalKey current;
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while (iter_->Valid() && !ParseKey(¤t)) {
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iter_->Prev();
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}
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if (iter_->Valid()) {
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SaveKey(current.user_key);
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}
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FindPrevUserEntry();
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}
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// Let X be the user key at which iter_ is currently positioned.
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// Adjust DBIter to point at the last entry with a key <= X that
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// has a live value.
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void DBIter::FindPrevUserEntry() {
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// Consider the following example:
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//
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// A@540
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// A@400
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//
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// B@300
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// B@200
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// B@100 <- iter_
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//
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// C@301
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// C@201
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//
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// The comments marked "(first iteration)" below relate what happens
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// for the preceding example in the first iteration of the while loop
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// below. There may be more than one iteration either if there are
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// no live values for B, or if there is a corruption.
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while (iter_->Valid()) {
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std::string saved = key_;
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bool found_live;
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ScanUntilBeforeCurrentKey(&found_live);
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// (first iteration) iter_ at A@400
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if (found_live) {
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// Step forward into range of entries with user key >= saved
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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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// (first iteration) iter_ at B@300
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FindNextUserEntry(); // Sets key_ to the key of the next value it found
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if (valid_ && user_comparator_->Compare(key_, saved) == 0) {
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// (first iteration) iter_ at C@301
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return;
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}
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// FindNextUserEntry() could not find any entries under the
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// user key "saved". This is probably a corruption since
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// ScanUntilBefore(saved) found a live value. So we skip
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// backwards to an earlier key and ignore the corrupted
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// entries for "saved".
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//
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// (first iteration) iter_ at C@301 and saved == "B"
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key_ = saved;
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bool ignored;
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ScanUntilBeforeCurrentKey(&ignored);
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// (first iteration) iter_ at A@400
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}
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}
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valid_ = false;
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key_.clear();
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value_.clear();
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}
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void DBIter::ScanUntilBeforeCurrentKey(bool* found_live) {
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*found_live = false;
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if (!iter_->Valid()) {
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iter_->SeekToLast();
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}
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while (iter_->Valid()) {
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ParsedInternalKey current;
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if (!ParseKey(¤t)) {
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iter_->Prev();
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continue;
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}
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if (current.sequence > sequence_) {
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// Ignore entries that are serialized after this read
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iter_->Prev();
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continue;
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}
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const int cmp = user_comparator_->Compare(current.user_key, key_);
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if (cmp < 0) {
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SaveKey(current.user_key);
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return;
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} else if (cmp == 0) {
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switch (current.type) {
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case kTypeDeletion:
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*found_live = false;
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break;
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case kTypeValue:
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case kTypeLargeValueRef:
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*found_live = true;
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break;
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}
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} else { // cmp > 0
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*found_live = false;
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}
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iter_->Prev();
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}
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}
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void DBIter::ReadIndirectValue() 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 (value_.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, value_.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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if (s.ok()) {
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uint64_t file_size = file->Size();
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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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