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rocksdb/db/db_iter.cc

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
// 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 <stdexcept>
#include <deque>
#include <string>
#include <limits>
#include "db/filename.h"
#include "db/dbformat.h"
#include "rocksdb/env.h"
#include "rocksdb/options.h"
#include "rocksdb/iterator.h"
#include "rocksdb/merge_operator.h"
#include "port/port.h"
#include "util/arena.h"
#include "util/logging.h"
#include "util/mutexlock.h"
#include "util/perf_context_imp.h"
namespace rocksdb {
#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
// 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:
// The following is grossly complicated. TODO: clean it up
// 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(Env* env, const Options& options, const Comparator* cmp,
Iterator* iter, SequenceNumber s, bool arena_mode,
const Slice* iterate_upper_bound = nullptr)
: arena_mode_(arena_mode),
env_(env),
logger_(options.info_log.get()),
user_comparator_(cmp),
user_merge_operator_(options.merge_operator.get()),
iter_(iter),
sequence_(s),
direction_(kForward),
valid_(false),
current_entry_is_merged_(false),
statistics_(options.statistics.get()),
iterate_upper_bound_(iterate_upper_bound) {
RecordTick(statistics_, NO_ITERATORS);
prefix_extractor_ = options.prefix_extractor.get();
max_skip_ = options.max_sequential_skip_in_iterations;
}
virtual ~DBIter() {
RecordTick(statistics_, NO_ITERATORS, -1);
if (!arena_mode_) {
delete iter_;
} else {
iter_->~Iterator();
}
}
virtual void SetIter(Iterator* iter) {
assert(iter_ == nullptr);
iter_ = iter;
}
virtual bool Valid() const { return valid_; }
virtual Slice key() const {
assert(valid_);
return saved_key_.GetKey();
}
virtual Slice value() const {
assert(valid_);
return (direction_ == kForward && !current_entry_is_merged_) ?
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 PrevInternal();
void FindParseableKey(ParsedInternalKey* ikey, Direction direction);
bool FindValueForCurrentKey();
bool FindValueForCurrentKeyUsingSeek();
void FindPrevUserKey();
void FindNextUserKey();
inline void FindNextUserEntry(bool skipping);
void FindNextUserEntryInternal(bool skipping);
bool ParseKey(ParsedInternalKey* key);
void MergeValuesNewToOld();
inline void ClearSavedValue() {
if (saved_value_.capacity() > 1048576) {
std::string empty;
swap(empty, saved_value_);
} else {
saved_value_.clear();
}
}
const SliceTransform* prefix_extractor_;
bool arena_mode_;
Env* const env_;
Logger* logger_;
const Comparator* const user_comparator_;
const MergeOperator* const user_merge_operator_;
Iterator* iter_;
SequenceNumber const sequence_;
Status status_;
IterKey saved_key_;
std::string saved_value_;
Direction direction_;
bool valid_;
bool current_entry_is_merged_;
Statistics* statistics_;
uint64_t max_skip_;
const Slice* iterate_upper_bound_;
// No copying allowed
DBIter(const DBIter&);
void operator=(const DBIter&);
};
inline bool DBIter::ParseKey(ParsedInternalKey* ikey) {
if (!ParseInternalKey(iter_->key(), ikey)) {
status_ = Status::Corruption("corrupted internal key in DBIter");
Log(logger_, "corrupted internal key in DBIter: %s",
iter_->key().ToString(true).c_str());
return false;
} else {
return true;
}
}
void DBIter::Next() {
assert(valid_);
if (direction_ == kReverse) {
FindNextUserKey();
direction_ = kForward;
if (!iter_->Valid()) {
iter_->SeekToFirst();
}
}
// If the current value is merged, we might already hit end of iter_
if (!iter_->Valid()) {
valid_ = false;
return;
}
FindNextUserEntry(true /* skipping the current user key */);
}
// PRE: saved_key_ has the current user key if skipping
// POST: saved_key_ should have the next user key if valid_,
// if the current entry is a result of merge
// current_entry_is_merged_ => true
// saved_value_ => the merged value
//
// NOTE: In between, saved_key_ can point to a user key that has
// a delete marker
inline void DBIter::FindNextUserEntry(bool skipping) {
PERF_TIMER_GUARD(find_next_user_entry_time);
FindNextUserEntryInternal(skipping);
}
// Actual implementation of DBIter::FindNextUserEntry()
void DBIter::FindNextUserEntryInternal(bool skipping) {
// Loop until we hit an acceptable entry to yield
assert(iter_->Valid());
assert(direction_ == kForward);
current_entry_is_merged_ = false;
uint64_t num_skipped = 0;
do {
ParsedInternalKey ikey;
if (ParseKey(&ikey)) {
if (iterate_upper_bound_ != nullptr &&
ikey.user_key.compare(*iterate_upper_bound_) >= 0) {
break;
}
if (ikey.sequence <= sequence_) {
if (skipping &&
user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) <= 0) {
num_skipped++; // skip this entry
PERF_COUNTER_ADD(internal_key_skipped_count, 1);
} else {
skipping = false;
switch (ikey.type) {
case kTypeDeletion:
// Arrange to skip all upcoming entries for this key since
// they are hidden by this deletion.
saved_key_.SetKey(ikey.user_key);
skipping = true;
num_skipped = 0;
PERF_COUNTER_ADD(internal_delete_skipped_count, 1);
break;
case kTypeValue:
valid_ = true;
saved_key_.SetKey(ikey.user_key);
return;
case kTypeMerge:
// By now, we are sure the current ikey is going to yield a value
saved_key_.SetKey(ikey.user_key);
current_entry_is_merged_ = true;
valid_ = true;
MergeValuesNewToOld(); // Go to a different state machine
return;
default:
assert(false);
break;
}
}
}
}
// If we have sequentially iterated via numerous keys and still not
// found the next user-key, then it is better to seek so that we can
// avoid too many key comparisons. We seek to the last occurence of
// our current key by looking for sequence number 0.
if (skipping && num_skipped > max_skip_) {
num_skipped = 0;
std::string last_key;
AppendInternalKey(&last_key, ParsedInternalKey(saved_key_.GetKey(), 0,
kValueTypeForSeek));
iter_->Seek(last_key);
RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION);
} else {
iter_->Next();
}
} while (iter_->Valid());
valid_ = false;
}
// Merge values of the same user key starting from the current iter_ position
// Scan from the newer entries to older entries.
// PRE: iter_->key() points to the first merge type entry
// saved_key_ stores the user key
// POST: saved_value_ has the merged value for the user key
// iter_ points to the next entry (or invalid)
void DBIter::MergeValuesNewToOld() {
if (!user_merge_operator_) {
Log(logger_, "Options::merge_operator is null.");
throw std::logic_error("DBIter::MergeValuesNewToOld() with"
" Options::merge_operator null");
}
// Start the merge process by pushing the first operand
std::deque<std::string> operands;
operands.push_front(iter_->value().ToString());
std::string merge_result; // Temporary string to hold merge result later
ParsedInternalKey ikey;
for (iter_->Next(); iter_->Valid(); iter_->Next()) {
if (!ParseKey(&ikey)) {
// skip corrupted key
continue;
}
if (user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) != 0) {
// hit the next user key, stop right here
break;
}
if (kTypeDeletion == ikey.type) {
// hit a delete with the same user key, stop right here
// iter_ is positioned after delete
iter_->Next();
break;
}
if (kTypeValue == ikey.type) {
// hit a put, merge the put value with operands and store the
// final result in saved_value_. We are done!
// ignore corruption if there is any.
const Slice value = iter_->value();
user_merge_operator_->FullMerge(ikey.user_key, &value, operands,
&saved_value_, logger_);
// iter_ is positioned after put
iter_->Next();
return;
}
if (kTypeMerge == ikey.type) {
// hit a merge, add the value as an operand and run associative merge.
// when complete, add result to operands and continue.
const Slice& value = iter_->value();
operands.push_front(value.ToString());
}
}
// we either exhausted all internal keys under this user key, or hit
// a deletion marker.
// feed null as the existing value to the merge operator, such that
// client can differentiate this scenario and do things accordingly.
user_merge_operator_->FullMerge(saved_key_.GetKey(), nullptr, operands,
&saved_value_, logger_);
}
void DBIter::Prev() {
assert(valid_);
if (direction_ == kForward) {
FindPrevUserKey();
direction_ = kReverse;
}
PrevInternal();
}
void DBIter::PrevInternal() {
if (!iter_->Valid()) {
valid_ = false;
return;
}
ParsedInternalKey ikey;
while (iter_->Valid()) {
saved_key_.SetKey(ExtractUserKey(iter_->key()));
if (FindValueForCurrentKey()) {
valid_ = true;
if (!iter_->Valid()) {
return;
}
FindParseableKey(&ikey, kReverse);
if (user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) == 0) {
FindPrevUserKey();
}
return;
}
if (!iter_->Valid()) {
break;
}
FindParseableKey(&ikey, kReverse);
if (user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) == 0) {
FindPrevUserKey();
}
}
// We haven't found any key - iterator is not valid
assert(!iter_->Valid());
valid_ = false;
}
// This function checks, if the entry with biggest sequence_number <= sequence_
// is non kTypeDeletion. If it's not, we save value in saved_value_
bool DBIter::FindValueForCurrentKey() {
assert(iter_->Valid());
// Contains operands for merge operator.
std::deque<std::string> operands;
// last entry before merge (could be kTypeDeletion or kTypeValue)
ValueType last_not_merge_type = kTypeDeletion;
ValueType last_key_entry_type = kTypeDeletion;
ParsedInternalKey ikey;
FindParseableKey(&ikey, kReverse);
size_t num_skipped = 0;
while (iter_->Valid() && ikey.sequence <= sequence_ &&
(user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) == 0)) {
// We iterate too much: let's use Seek() to avoid too much key comparisons
if (num_skipped >= max_skip_) {
return FindValueForCurrentKeyUsingSeek();
}
last_key_entry_type = ikey.type;
switch (last_key_entry_type) {
case kTypeValue:
operands.clear();
saved_value_ = iter_->value().ToString();
last_not_merge_type = kTypeValue;
break;
case kTypeDeletion:
operands.clear();
last_not_merge_type = kTypeDeletion;
PERF_COUNTER_ADD(internal_delete_skipped_count, 1);
break;
case kTypeMerge:
assert(user_merge_operator_ != nullptr);
operands.push_back(iter_->value().ToString());
break;
default:
assert(false);
}
PERF_COUNTER_ADD(internal_key_skipped_count, 1);
assert(user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) == 0);
iter_->Prev();
++num_skipped;
FindParseableKey(&ikey, kReverse);
}
switch (last_key_entry_type) {
case kTypeDeletion:
valid_ = false;
return false;
case kTypeMerge:
if (last_not_merge_type == kTypeDeletion) {
user_merge_operator_->FullMerge(saved_key_.GetKey(), nullptr, operands,
&saved_value_, logger_);
} else {
assert(last_not_merge_type == kTypeValue);
std::string last_put_value = saved_value_;
Slice temp_slice(last_put_value);
user_merge_operator_->FullMerge(saved_key_.GetKey(), &temp_slice,
operands, &saved_value_, logger_);
}
break;
case kTypeValue:
// do nothing - we've already has value in saved_value_
break;
default:
assert(false);
break;
}
valid_ = true;
return true;
}
// This function is used in FindValueForCurrentKey.
// We use Seek() function instead of Prev() to find necessary value
bool DBIter::FindValueForCurrentKeyUsingSeek() {
std::string last_key;
AppendInternalKey(&last_key, ParsedInternalKey(saved_key_.GetKey(), sequence_,
kValueTypeForSeek));
iter_->Seek(last_key);
RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION);
// assume there is at least one parseable key for this user key
ParsedInternalKey ikey;
FindParseableKey(&ikey, kForward);
if (ikey.type == kTypeValue || ikey.type == kTypeDeletion) {
if (ikey.type == kTypeValue) {
saved_value_ = iter_->value().ToString();
valid_ = true;
return true;
}
valid_ = false;
return false;
}
// kTypeMerge. We need to collect all kTypeMerge values and save them
// in operands
std::deque<std::string> operands;
while (iter_->Valid() &&
(user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) == 0) &&
ikey.type == kTypeMerge) {
operands.push_front(iter_->value().ToString());
iter_->Next();
FindParseableKey(&ikey, kForward);
}
if (!iter_->Valid() ||
(user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) != 0) ||
ikey.type == kTypeDeletion) {
user_merge_operator_->FullMerge(saved_key_.GetKey(), nullptr, operands,
&saved_value_, logger_);
// Make iter_ valid and point to saved_key_
if (!iter_->Valid() ||
(user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) != 0)) {
iter_->Seek(last_key);
RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION);
}
valid_ = true;
return true;
}
const Slice& value = iter_->value();
user_merge_operator_->FullMerge(saved_key_.GetKey(), &value, operands,
&saved_value_, logger_);
valid_ = true;
return true;
}
// Used in Next to change directions
// Go to next user key
// Don't use Seek(),
// because next user key will be very close
void DBIter::FindNextUserKey() {
if (!iter_->Valid()) {
return;
}
ParsedInternalKey ikey;
FindParseableKey(&ikey, kForward);
while (iter_->Valid() &&
user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) != 0) {
iter_->Next();
FindParseableKey(&ikey, kForward);
}
}
// Go to previous user_key
void DBIter::FindPrevUserKey() {
if (!iter_->Valid()) {
return;
}
size_t num_skipped = 0;
ParsedInternalKey ikey;
FindParseableKey(&ikey, kReverse);
while (iter_->Valid() &&
user_comparator_->Compare(ikey.user_key, saved_key_.GetKey()) == 0) {
if (num_skipped >= max_skip_) {
num_skipped = 0;
IterKey last_key;
last_key.SetInternalKey(ParsedInternalKey(
saved_key_.GetKey(), kMaxSequenceNumber, kValueTypeForSeek));
iter_->Seek(last_key.GetKey());
RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION);
}
iter_->Prev();
++num_skipped;
FindParseableKey(&ikey, kReverse);
}
}
// Skip all unparseable keys
void DBIter::FindParseableKey(ParsedInternalKey* ikey, Direction direction) {
while (iter_->Valid() && !ParseKey(ikey)) {
if (direction == kReverse) {
iter_->Prev();
} else {
iter_->Next();
}
}
}
void DBIter::Seek(const Slice& target) {
StopWatch sw(env_, statistics_, DB_SEEK);
// total ordering is not guaranteed if prefix_extractor is set
// hence prefix based seeks will not give correct results
if (iterate_upper_bound_ != nullptr && prefix_extractor_ != nullptr) {
if (!prefix_extractor_->InDomain(*iterate_upper_bound_) ||
!prefix_extractor_->InDomain(target) ||
prefix_extractor_->Transform(*iterate_upper_bound_).compare(
prefix_extractor_->Transform(target)) != 0) {
status_ = Status::InvalidArgument("read_options.iterate_*_bound "
" and seek target need to have the same prefix.");
valid_ = false;
return;
}
}
saved_key_.Clear();
// now savved_key is used to store internal key.
saved_key_.SetInternalKey(target, sequence_);
{
PERF_TIMER_GUARD(seek_internal_seek_time);
iter_->Seek(saved_key_.GetKey());
}
if (iter_->Valid()) {
direction_ = kForward;
ClearSavedValue();
FindNextUserEntry(false /*not skipping */);
} else {
valid_ = false;
}
}
void DBIter::SeekToFirst() {
// Don't use iter_::Seek() if we set a prefix extractor
// because prefix seek wiil be used.
if (prefix_extractor_ != nullptr) {
max_skip_ = std::numeric_limits<uint64_t>::max();
}
direction_ = kForward;
ClearSavedValue();
{
PERF_TIMER_GUARD(seek_internal_seek_time);
iter_->SeekToFirst();
}
if (iter_->Valid()) {
FindNextUserEntry(false /* not skipping */);
} else {
valid_ = false;
}
}
void DBIter::SeekToLast() {
// Don't use iter_::Seek() if we set a prefix extractor
// because prefix seek wiil be used.
if (prefix_extractor_ != nullptr) {
max_skip_ = std::numeric_limits<uint64_t>::max();
}
direction_ = kReverse;
ClearSavedValue();
{
PERF_TIMER_GUARD(seek_internal_seek_time);
iter_->SeekToLast();
}
PrevInternal();
}
Iterator* NewDBIterator(Env* env, const Options& options,
const Comparator* user_key_comparator,
Iterator* internal_iter,
const SequenceNumber& sequence,
const Slice* iterate_upper_bound) {
return new DBIter(env, options, user_key_comparator, internal_iter, sequence,
false, iterate_upper_bound);
}
ArenaWrappedDBIter::~ArenaWrappedDBIter() { db_iter_->~DBIter(); }
void ArenaWrappedDBIter::SetDBIter(DBIter* iter) { db_iter_ = iter; }
void ArenaWrappedDBIter::SetIterUnderDBIter(Iterator* iter) {
static_cast<DBIter*>(db_iter_)->SetIter(iter);
}
inline bool ArenaWrappedDBIter::Valid() const { return db_iter_->Valid(); }
inline void ArenaWrappedDBIter::SeekToFirst() { db_iter_->SeekToFirst(); }
inline void ArenaWrappedDBIter::SeekToLast() { db_iter_->SeekToLast(); }
inline void ArenaWrappedDBIter::Seek(const Slice& target) {
db_iter_->Seek(target);
}
inline void ArenaWrappedDBIter::Next() { db_iter_->Next(); }
inline void ArenaWrappedDBIter::Prev() { db_iter_->Prev(); }
inline Slice ArenaWrappedDBIter::key() const { return db_iter_->key(); }
inline Slice ArenaWrappedDBIter::value() const { return db_iter_->value(); }
inline Status ArenaWrappedDBIter::status() const { return db_iter_->status(); }
void ArenaWrappedDBIter::RegisterCleanup(CleanupFunction function, void* arg1,
void* arg2) {
db_iter_->RegisterCleanup(function, arg1, arg2);
}
ArenaWrappedDBIter* NewArenaWrappedDbIterator(
Env* env, const Options& options, const Comparator* user_key_comparator,
const SequenceNumber& sequence,
const Slice* iterate_upper_bound) {
ArenaWrappedDBIter* iter = new ArenaWrappedDBIter();
Arena* arena = iter->GetArena();
auto mem = arena->AllocateAligned(sizeof(DBIter));
DBIter* db_iter = new (mem) DBIter(env, options, user_key_comparator,
nullptr, sequence, true, iterate_upper_bound);
iter->SetDBIter(db_iter);
return iter;
}
} // namespace rocksdb
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