src/leveldb/db/db_iter.cc
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include "db/db_iter.h"
#include "db/filename.h"
#include "db/db_impl.h"
#include "db/dbformat.h"
#include "leveldb/env.h"
#include "leveldb/iterator.h"
#include "port/port.h"
#include "util/logging.h"
#include "util/mutexlock.h"
#include "util/random.h"
namespace leveldb {
#if 0
static void DumpInternalIter(Iterator* iter) {
for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
ParsedInternalKey k;
if (!ParseInternalKey(iter->key(), &k)) {
fprintf(stderr, "Corrupt '%s'\n", EscapeString(iter->key()).c_str());
} else {
fprintf(stderr, "@ '%s'\n", k.DebugString().c_str());
}
}
}
#endif
namespace {
// Memtables and sstables that make the DB representation contain
// (userkey,seq,type) => uservalue entries. DBIter
// combines multiple entries for the same userkey found in the DB
// representation into a single entry while accounting for sequence
// numbers, deletion markers, overwrites, etc.
class DBIter: public Iterator {
public:
// Which direction is the iterator currently moving?
// (1) When moving forward, the internal iterator is positioned at
// the exact entry that yields this->key(), this->value()
// (2) When moving backwards, the internal iterator is positioned
// just before all entries whose user key == this->key().
enum Direction {
kForward,
kReverse
};
DBIter(DBImpl* db, const Comparator* cmp, Iterator* iter, SequenceNumber s,
uint32_t seed)
: db_(db),
user_comparator_(cmp),
iter_(iter),
sequence_(s),
direction_(kForward),
valid_(false),
rnd_(seed),
bytes_counter_(RandomPeriod()) {
}
virtual ~DBIter() {
delete iter_;
}
virtual bool Valid() const { return valid_; }
virtual Slice key() const {
assert(valid_);
return (direction_ == kForward) ? ExtractUserKey(iter_->key()) : saved_key_;
}
virtual Slice value() const {
assert(valid_);
return (direction_ == kForward) ? iter_->value() : saved_value_;
}
virtual Status status() const {
if (status_.ok()) {
return iter_->status();
} else {
return status_;
}
}
virtual void Next();
virtual void Prev();
virtual void Seek(const Slice& target);
virtual void SeekToFirst();
virtual void SeekToLast();
private:
void FindNextUserEntry(bool skipping, std::string* skip);
void FindPrevUserEntry();
bool ParseKey(ParsedInternalKey* key);
inline void SaveKey(const Slice& k, std::string* dst) {
dst->assign(k.data(), k.size());
}
inline void ClearSavedValue() {
if (saved_value_.capacity() > 1048576) {
std::string empty;
swap(empty, saved_value_);
} else {
saved_value_.clear();
}
}
// Pick next gap with average value of config::kReadBytesPeriod.
ssize_t RandomPeriod() {
return rnd_.Uniform(2*config::kReadBytesPeriod);
}
DBImpl* db_;
const Comparator* const user_comparator_;
Iterator* const iter_;
SequenceNumber const sequence_;
Status status_;
std::string saved_key_; // == current key when direction_==kReverse
std::string saved_value_; // == current raw value when direction_==kReverse
Direction direction_;
bool valid_;
Random rnd_;
ssize_t bytes_counter_;
// No copying allowed
DBIter(const DBIter&);
void operator=(const DBIter&);
};
inline bool DBIter::ParseKey(ParsedInternalKey* ikey) {
Slice k = iter_->key();
ssize_t n = k.size() + iter_->value().size();
bytes_counter_ -= n;
while (bytes_counter_ < 0) {
bytes_counter_ += RandomPeriod();
db_->RecordReadSample(k);
}
if (!ParseInternalKey(k, ikey)) {
status_ = Status::Corruption("corrupted internal key in DBIter");
return false;
} else {
return true;
}
}
void DBIter::Next() {
assert(valid_);
if (direction_ == kReverse) { // Switch directions?
direction_ = kForward;
// iter_ is pointing just before the entries for this->key(),
// so advance into the range of entries for this->key() and then
// use the normal skipping code below.
if (!iter_->Valid()) {
iter_->SeekToFirst();
} else {
iter_->Next();
}
if (!iter_->Valid()) {
valid_ = false;
saved_key_.clear();
return;
}
// saved_key_ already contains the key to skip past.
} else {
// Store in saved_key_ the current key so we skip it below.
SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
}
FindNextUserEntry(true, &saved_key_);
}
void DBIter::FindNextUserEntry(bool skipping, std::string* skip) {
// Loop until we hit an acceptable entry to yield
assert(iter_->Valid());
assert(direction_ == kForward);
do {
ParsedInternalKey ikey;
if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
switch (ikey.type) {
case kTypeDeletion:
// Arrange to skip all upcoming entries for this key since
// they are hidden by this deletion.
SaveKey(ikey.user_key, skip);
skipping = true;
break;
case kTypeValue:
if (skipping &&
user_comparator_->Compare(ikey.user_key, *skip) <= 0) {
// Entry hidden
} else {
valid_ = true;
saved_key_.clear();
return;
}
break;
}
}
iter_->Next();
} while (iter_->Valid());
saved_key_.clear();
valid_ = false;
}
void DBIter::Prev() {
assert(valid_);
if (direction_ == kForward) { // Switch directions?
// iter_ is pointing at the current entry. Scan backwards until
// the key changes so we can use the normal reverse scanning code.
assert(iter_->Valid()); // Otherwise valid_ would have been false
SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
while (true) {
iter_->Prev();
if (!iter_->Valid()) {
valid_ = false;
saved_key_.clear();
ClearSavedValue();
return;
}
if (user_comparator_->Compare(ExtractUserKey(iter_->key()),
saved_key_) < 0) {
break;
}
}
direction_ = kReverse;
}
FindPrevUserEntry();
}
void DBIter::FindPrevUserEntry() {
assert(direction_ == kReverse);
ValueType value_type = kTypeDeletion;
if (iter_->Valid()) {
do {
ParsedInternalKey ikey;
if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
if ((value_type != kTypeDeletion) &&
user_comparator_->Compare(ikey.user_key, saved_key_) < 0) {
// We encountered a non-deleted value in entries for previous keys,
break;
}
value_type = ikey.type;
if (value_type == kTypeDeletion) {
saved_key_.clear();
ClearSavedValue();
} else {
Slice raw_value = iter_->value();
if (saved_value_.capacity() > raw_value.size() + 1048576) {
std::string empty;
swap(empty, saved_value_);
}
SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
saved_value_.assign(raw_value.data(), raw_value.size());
}
}
iter_->Prev();
} while (iter_->Valid());
}
if (value_type == kTypeDeletion) {
// End
valid_ = false;
saved_key_.clear();
ClearSavedValue();
direction_ = kForward;
} else {
valid_ = true;
}
}
void DBIter::Seek(const Slice& target) {
direction_ = kForward;
ClearSavedValue();
saved_key_.clear();
AppendInternalKey(
&saved_key_, ParsedInternalKey(target, sequence_, kValueTypeForSeek));
iter_->Seek(saved_key_);
if (iter_->Valid()) {
FindNextUserEntry(false, &saved_key_ /* temporary storage */);
} else {
valid_ = false;
}
}
void DBIter::SeekToFirst() {
direction_ = kForward;
ClearSavedValue();
iter_->SeekToFirst();
if (iter_->Valid()) {
FindNextUserEntry(false, &saved_key_ /* temporary storage */);
} else {
valid_ = false;
}
}
void DBIter::SeekToLast() {
direction_ = kReverse;
ClearSavedValue();
iter_->SeekToLast();
FindPrevUserEntry();
}
} // anonymous namespace
Iterator* NewDBIterator(
DBImpl* db,
const Comparator* user_key_comparator,
Iterator* internal_iter,
SequenceNumber sequence,
uint32_t seed) {
return new DBIter(db, user_key_comparator, internal_iter, sequence, seed);
}
} // namespace leveldb