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rocksdb/db/db_iter.cc
anand1976 d394a6bb48 Add a ticker stat for number of keys skipped during iteration 
Summary:
This diff adds a new ticker stat, NUMBER_ITER_SKIP, to count the
number of internal keys skipped during iteration. Keys can be skipped
due to deletes, or lower sequence number, or higher sequence number
than the one requested.

Also, fix the issue when StatisticsData is naturally aligned on cacheline boundary,
padding becomes a zero size array, which the Windows compiler doesn't
like. So add a cacheline worth of padding in that case to keep it happy.
We cannot conditionally add padding as gcc doesn't allow using sizeof
in preprocessor directives.
Closes https://github.com/facebook/rocksdb/pull/3177

Differential Revision: D6353897

Pulled By: anand1976

fbshipit-source-id: 441d5a09af9c4e22e7355242dfc0c7b27aa0a6c2
2017-11-20 21:26:37 -08:00

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root 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 <string>
#include <iostream>
#include <limits>
#include "db/dbformat.h"
#include "db/merge_context.h"
#include "db/merge_helper.h"
#include "db/pinned_iterators_manager.h"
#include "monitoring/perf_context_imp.h"
#include "rocksdb/env.h"
#include "rocksdb/iterator.h"
#include "rocksdb/merge_operator.h"
#include "rocksdb/options.h"
#include "table/internal_iterator.h"
#include "util/arena.h"
#include "util/filename.h"
#include "util/logging.h"
#include "util/mutexlock.h"
#include "util/string_util.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 final: 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
};
// LocalStatistics contain Statistics counters that will be aggregated per
// each iterator instance and then will be sent to the global statistics when
// the iterator is destroyed.
//
// The purpose of this approach is to avoid perf regression happening
// when multiple threads bump the atomic counters from a DBIter::Next().
struct LocalStatistics {
explicit LocalStatistics() { ResetCounters(); }
void ResetCounters() {
next_count_ = 0;
next_found_count_ = 0;
prev_count_ = 0;
prev_found_count_ = 0;
bytes_read_ = 0;
skip_count_ = 0;
}
void BumpGlobalStatistics(Statistics* global_statistics) {
RecordTick(global_statistics, NUMBER_DB_NEXT, next_count_);
RecordTick(global_statistics, NUMBER_DB_NEXT_FOUND, next_found_count_);
RecordTick(global_statistics, NUMBER_DB_PREV, prev_count_);
RecordTick(global_statistics, NUMBER_DB_PREV_FOUND, prev_found_count_);
RecordTick(global_statistics, ITER_BYTES_READ, bytes_read_);
RecordTick(global_statistics, NUMBER_ITER_SKIP, skip_count_);
PERF_COUNTER_ADD(iter_read_bytes, bytes_read_);
ResetCounters();
}
// Map to Tickers::NUMBER_DB_NEXT
uint64_t next_count_;
// Map to Tickers::NUMBER_DB_NEXT_FOUND
uint64_t next_found_count_;
// Map to Tickers::NUMBER_DB_PREV
uint64_t prev_count_;
// Map to Tickers::NUMBER_DB_PREV_FOUND
uint64_t prev_found_count_;
// Map to Tickers::ITER_BYTES_READ
uint64_t bytes_read_;
// Map to Tickers::NUMBER_ITER_SKIP
uint64_t skip_count_;
};
DBIter(Env* _env, const ReadOptions& read_options,
const ImmutableCFOptions& cf_options, const Comparator* cmp,
InternalIterator* iter, SequenceNumber s, bool arena_mode,
uint64_t max_sequential_skip_in_iterations,
ReadCallback* read_callback, bool allow_blob)
: arena_mode_(arena_mode),
env_(_env),
logger_(cf_options.info_log),
user_comparator_(cmp),
merge_operator_(cf_options.merge_operator),
iter_(iter),
sequence_(s),
direction_(kForward),
valid_(false),
current_entry_is_merged_(false),
statistics_(cf_options.statistics),
num_internal_keys_skipped_(0),
iterate_lower_bound_(read_options.iterate_lower_bound),
iterate_upper_bound_(read_options.iterate_upper_bound),
prefix_same_as_start_(read_options.prefix_same_as_start),
pin_thru_lifetime_(read_options.pin_data),
total_order_seek_(read_options.total_order_seek),
range_del_agg_(cf_options.internal_comparator, s,
true /* collapse_deletions */),
read_callback_(read_callback),
allow_blob_(allow_blob),
is_blob_(false),
start_seqnum_(read_options.iter_start_seqnum) {
RecordTick(statistics_, NO_ITERATORS);
prefix_extractor_ = cf_options.prefix_extractor;
max_skip_ = max_sequential_skip_in_iterations;
max_skippable_internal_keys_ = read_options.max_skippable_internal_keys;
if (pin_thru_lifetime_) {
pinned_iters_mgr_.StartPinning();
}
if (iter_) {
iter_->SetPinnedItersMgr(&pinned_iters_mgr_);
}
}
virtual ~DBIter() {
// Release pinned data if any
if (pinned_iters_mgr_.PinningEnabled()) {
pinned_iters_mgr_.ReleasePinnedData();
}
// Compiler warning issue filed:
// https://github.com/facebook/rocksdb/issues/3013
RecordTick(statistics_, NO_ITERATORS, uint64_t(-1));
ResetInternalKeysSkippedCounter();
local_stats_.BumpGlobalStatistics(statistics_);
if (!arena_mode_) {
delete iter_;
} else {
iter_->~InternalIterator();
}
}
virtual void SetIter(InternalIterator* iter) {
assert(iter_ == nullptr);
iter_ = iter;
iter_->SetPinnedItersMgr(&pinned_iters_mgr_);
}
virtual RangeDelAggregator* GetRangeDelAggregator() {
return &range_del_agg_;
}
virtual bool Valid() const override { return valid_; }
virtual Slice key() const override {
assert(valid_);
if(start_seqnum_ > 0) {
return saved_key_.GetInternalKey();
} else {
return saved_key_.GetUserKey();
}
}
virtual Slice value() const override {
assert(valid_);
if (current_entry_is_merged_) {
// If pinned_value_ is set then the result of merge operator is one of
// the merge operands and we should return it.
return pinned_value_.data() ? pinned_value_ : saved_value_;
} else if (direction_ == kReverse) {
return pinned_value_;
} else {
return iter_->value();
}
}
virtual Status status() const override {
if (status_.ok()) {
return iter_->status();
} else {
return status_;
}
}
bool IsBlob() const {
assert(valid_ && (allow_blob_ || !is_blob_));
return is_blob_;
}
virtual Status GetProperty(std::string prop_name,
std::string* prop) override {
if (prop == nullptr) {
return Status::InvalidArgument("prop is nullptr");
}
if (prop_name == "rocksdb.iterator.super-version-number") {
// First try to pass the value returned from inner iterator.
return iter_->GetProperty(prop_name, prop);
} else if (prop_name == "rocksdb.iterator.is-key-pinned") {
if (valid_) {
*prop = (pin_thru_lifetime_ && saved_key_.IsKeyPinned()) ? "1" : "0";
} else {
*prop = "Iterator is not valid.";
}
return Status::OK();
}
return Status::InvalidArgument("Undentified property.");
}
virtual void Next() override;
virtual void Prev() override;
virtual void Seek(const Slice& target) override;
virtual void SeekForPrev(const Slice& target) override;
virtual void SeekToFirst() override;
virtual void SeekToLast() override;
Env* env() { return env_; }
void set_sequence(uint64_t s) { sequence_ = s; }
void set_valid(bool v) { valid_ = v; }
private:
void ReverseToForward();
void ReverseToBackward();
void PrevInternal();
void FindParseableKey(ParsedInternalKey* ikey, Direction direction);
bool FindValueForCurrentKey();
bool FindValueForCurrentKeyUsingSeek();
void FindPrevUserKey();
void FindNextUserKey();
inline void FindNextUserEntry(bool skipping, bool prefix_check);
void FindNextUserEntryInternal(bool skipping, bool prefix_check);
bool ParseKey(ParsedInternalKey* key);
void MergeValuesNewToOld();
bool TooManyInternalKeysSkipped(bool increment = true);
bool IsVisible(SequenceNumber sequence);
// Temporarily pin the blocks that we encounter until ReleaseTempPinnedData()
// is called
void TempPinData() {
if (!pin_thru_lifetime_) {
pinned_iters_mgr_.StartPinning();
}
}
// Release blocks pinned by TempPinData()
void ReleaseTempPinnedData() {
if (!pin_thru_lifetime_ && pinned_iters_mgr_.PinningEnabled()) {
pinned_iters_mgr_.ReleasePinnedData();
}
}
inline void ClearSavedValue() {
if (saved_value_.capacity() > 1048576) {
std::string empty;
swap(empty, saved_value_);
} else {
saved_value_.clear();
}
}
inline void ResetInternalKeysSkippedCounter() {
local_stats_.skip_count_ += num_internal_keys_skipped_;
if (valid_) {
local_stats_.skip_count_--;
}
num_internal_keys_skipped_ = 0;
}
const SliceTransform* prefix_extractor_;
bool arena_mode_;
Env* const env_;
Logger* logger_;
const Comparator* const user_comparator_;
const MergeOperator* const merge_operator_;
InternalIterator* iter_;
SequenceNumber sequence_;
Status status_;
IterKey saved_key_;
// Reusable internal key data structure. This is only used inside one function
// and should not be used across functions. Reusing this object can reduce
// overhead of calling construction of the function if creating it each time.
ParsedInternalKey ikey_;
std::string saved_value_;
Slice pinned_value_;
Direction direction_;
bool valid_;
bool current_entry_is_merged_;
// for prefix seek mode to support prev()
Statistics* statistics_;
uint64_t max_skip_;
uint64_t max_skippable_internal_keys_;
uint64_t num_internal_keys_skipped_;
const Slice* iterate_lower_bound_;
const Slice* iterate_upper_bound_;
IterKey prefix_start_buf_;
Slice prefix_start_key_;
const bool prefix_same_as_start_;
// Means that we will pin all data blocks we read as long the Iterator
// is not deleted, will be true if ReadOptions::pin_data is true
const bool pin_thru_lifetime_;
const bool total_order_seek_;
// List of operands for merge operator.
MergeContext merge_context_;
RangeDelAggregator range_del_agg_;
LocalStatistics local_stats_;
PinnedIteratorsManager pinned_iters_mgr_;
ReadCallback* read_callback_;
bool allow_blob_;
bool is_blob_;
// for diff snapshots we want the lower bound on the seqnum;
// if this value > 0 iterator will return internal keys
SequenceNumber start_seqnum_;
// 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");
ROCKS_LOG_ERROR(logger_, "corrupted internal key in DBIter: %s",
iter_->key().ToString(true).c_str());
return false;
} else {
return true;
}
}
void DBIter::Next() {
assert(valid_);
// Release temporarily pinned blocks from last operation
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
if (direction_ == kReverse) {
ReverseToForward();
} else if (iter_->Valid() && !current_entry_is_merged_) {
// If the current value is not a merge, the iter position is the
// current key, which is already returned. We can safely issue a
// Next() without checking the current key.
// If the current key is a merge, very likely iter already points
// to the next internal position.
iter_->Next();
PERF_COUNTER_ADD(internal_key_skipped_count, 1);
}
if (statistics_ != nullptr) {
local_stats_.next_count_++;
}
// Now we point to the next internal position, for both of merge and
// not merge cases.
if (!iter_->Valid()) {
valid_ = false;
return;
}
FindNextUserEntry(true /* skipping the current user key */, prefix_same_as_start_);
if (statistics_ != nullptr && valid_) {
local_stats_.next_found_count_++;
local_stats_.bytes_read_ += (key().size() + value().size());
}
}
// 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 or a sequence number higher than sequence_
// saved_key_ MUST have a proper user_key before calling this function
//
// The prefix_check parameter controls whether we check the iterated
// keys against the prefix of the seeked key. Set to false when
// performing a seek without a key (e.g. SeekToFirst). Set to
// prefix_same_as_start_ for other iterations.
inline void DBIter::FindNextUserEntry(bool skipping, bool prefix_check) {
PERF_TIMER_GUARD(find_next_user_entry_time);
FindNextUserEntryInternal(skipping, prefix_check);
}
// Actual implementation of DBIter::FindNextUserEntry()
void DBIter::FindNextUserEntryInternal(bool skipping, bool prefix_check) {
// Loop until we hit an acceptable entry to yield
assert(iter_->Valid());
assert(direction_ == kForward);
current_entry_is_merged_ = false;
// How many times in a row we have skipped an entry with user key less than
// or equal to saved_key_. We could skip these entries either because
// sequence numbers were too high or because skipping = true.
// What saved_key_ contains throughout this method:
// - if skipping : saved_key_ contains the key that we need to skip,
// and we haven't seen any keys greater than that,
// - if num_skipped > 0 : saved_key_ contains the key that we have skipped
// num_skipped times, and we haven't seen any keys
// greater than that,
// - none of the above : saved_key_ can contain anything, it doesn't matter.
uint64_t num_skipped = 0;
is_blob_ = false;
do {
if (!ParseKey(&ikey_)) {
// Skip corrupted keys.
iter_->Next();
continue;
}
if (iterate_upper_bound_ != nullptr &&
user_comparator_->Compare(ikey_.user_key, *iterate_upper_bound_) >= 0) {
break;
}
if (prefix_extractor_ && prefix_check &&
prefix_extractor_->Transform(ikey_.user_key)
.compare(prefix_start_key_) != 0) {
break;
}
if (TooManyInternalKeysSkipped()) {
return;
}
if (IsVisible(ikey_.sequence)) {
if (skipping && user_comparator_->Compare(ikey_.user_key,
saved_key_.GetUserKey()) <= 0) {
num_skipped++; // skip this entry
PERF_COUNTER_ADD(internal_key_skipped_count, 1);
} else {
num_skipped = 0;
switch (ikey_.type) {
case kTypeDeletion:
case kTypeSingleDeletion:
// Arrange to skip all upcoming entries for this key since
// they are hidden by this deletion.
// if iterartor specified start_seqnum we
// 1) return internal key, including the type
// 2) return ikey only if ikey.seqnum >= start_seqnum_
// not that if deletion seqnum is < start_seqnum_ we
// just skip it like in normal iterator.
if (start_seqnum_ > 0 && ikey_.sequence >= start_seqnum_) {
saved_key_.SetInternalKey(ikey_);
valid_=true;
return;
} else {
saved_key_.SetUserKey(
ikey_.user_key,
!pin_thru_lifetime_ || !iter_->IsKeyPinned() /* copy */);
skipping = true;
PERF_COUNTER_ADD(internal_delete_skipped_count, 1);
}
break;
case kTypeValue:
case kTypeBlobIndex:
if (start_seqnum_ > 0) {
// we are taking incremental snapshot here
// incremental snapshots aren't supported on DB with range deletes
assert(!(
(ikey_.type == kTypeBlobIndex) && (start_seqnum_ > 0)
));
if (ikey_.sequence >= start_seqnum_) {
saved_key_.SetInternalKey(ikey_);
valid_ = true;
return;
} else {
// this key and all previous versions shouldn't be included,
// skipping
saved_key_.SetUserKey(ikey_.user_key,
!pin_thru_lifetime_ || !iter_->IsKeyPinned() /* copy */);
skipping = true;
}
} else {
saved_key_.SetUserKey(
ikey_.user_key,
!pin_thru_lifetime_ || !iter_->IsKeyPinned() /* copy */);
if (range_del_agg_.ShouldDelete(
ikey_, RangeDelAggregator::RangePositioningMode::
kForwardTraversal)) {
// Arrange to skip all upcoming entries for this key since
// they are hidden by this deletion.
skipping = true;
num_skipped = 0;
PERF_COUNTER_ADD(internal_delete_skipped_count, 1);
} else if (ikey_.type == kTypeBlobIndex) {
if (!allow_blob_) {
ROCKS_LOG_ERROR(logger_, "Encounter unexpected blob index.");
status_ = Status::NotSupported(
"Encounter unexpected blob index. Please open DB with "
"rocksdb::blob_db::BlobDB instead.");
valid_ = false;
} else {
is_blob_ = true;
valid_ = true;
}
return;
} else {
valid_ = true;
return;
}
}
break;
case kTypeMerge:
saved_key_.SetUserKey(
ikey_.user_key,
!pin_thru_lifetime_ || !iter_->IsKeyPinned() /* copy */);
if (range_del_agg_.ShouldDelete(
ikey_, RangeDelAggregator::RangePositioningMode::
kForwardTraversal)) {
// Arrange to skip all upcoming entries for this key since
// they are hidden by this deletion.
skipping = true;
num_skipped = 0;
PERF_COUNTER_ADD(internal_delete_skipped_count, 1);
} else {
// By now, we are sure the current ikey is going to yield a
// value
current_entry_is_merged_ = true;
valid_ = true;
MergeValuesNewToOld(); // Go to a different state machine
return;
}
break;
default:
assert(false);
break;
}
}
} else {
// This key was inserted after our snapshot was taken.
PERF_COUNTER_ADD(internal_recent_skipped_count, 1);
// Here saved_key_ may contain some old key, or the default empty key, or
// key assigned by some random other method. We don't care.
if (user_comparator_->Compare(ikey_.user_key, saved_key_.GetUserKey()) <=
0) {
num_skipped++;
} else {
saved_key_.SetUserKey(
ikey_.user_key,
!iter_->IsKeyPinned() || !pin_thru_lifetime_ /* copy */);
skipping = false;
num_skipped = 0;
}
}
// If we have sequentially iterated via numerous equal keys, then it's
// better to seek so that we can avoid too many key comparisons.
if (num_skipped > max_skip_) {
num_skipped = 0;
std::string last_key;
if (skipping) {
// We're looking for the next user-key but all we see are the same
// user-key with decreasing sequence numbers. Fast forward to
// sequence number 0 and type deletion (the smallest type).
AppendInternalKey(&last_key, ParsedInternalKey(saved_key_.GetUserKey(),
0, kTypeDeletion));
// Don't set skipping = false because we may still see more user-keys
// equal to saved_key_.
} else {
// We saw multiple entries with this user key and sequence numbers
// higher than sequence_. Fast forward to sequence_.
// Note that this only covers a case when a higher key was overwritten
// many times since our snapshot was taken, not the case when a lot of
// different keys were inserted after our snapshot was taken.
AppendInternalKey(&last_key,
ParsedInternalKey(saved_key_.GetUserKey(), sequence_,
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 (!merge_operator_) {
ROCKS_LOG_ERROR(logger_, "Options::merge_operator is null.");
status_ = Status::InvalidArgument("merge_operator_ must be set.");
valid_ = false;
return;
}
// Temporarily pin the blocks that hold merge operands
TempPinData();
merge_context_.Clear();
// Start the merge process by pushing the first operand
merge_context_.PushOperand(iter_->value(),
iter_->IsValuePinned() /* operand_pinned */);
ParsedInternalKey ikey;
Status s;
for (iter_->Next(); iter_->Valid(); iter_->Next()) {
if (!ParseKey(&ikey)) {
// skip corrupted key
continue;
}
if (!user_comparator_->Equal(ikey.user_key, saved_key_.GetUserKey())) {
// hit the next user key, stop right here
break;
} else if (kTypeDeletion == ikey.type || kTypeSingleDeletion == ikey.type ||
range_del_agg_.ShouldDelete(
ikey, RangeDelAggregator::RangePositioningMode::
kForwardTraversal)) {
// hit a delete with the same user key, stop right here
// iter_ is positioned after delete
iter_->Next();
break;
} else 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 val = iter_->value();
s = MergeHelper::TimedFullMerge(
merge_operator_, ikey.user_key, &val, merge_context_.GetOperands(),
&saved_value_, logger_, statistics_, env_, &pinned_value_, true);
if (!s.ok()) {
status_ = s;
}
// iter_ is positioned after put
iter_->Next();
return;
} else 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.
merge_context_.PushOperand(iter_->value(),
iter_->IsValuePinned() /* operand_pinned */);
PERF_COUNTER_ADD(internal_merge_count, 1);
} else if (kTypeBlobIndex == ikey.type) {
if (!allow_blob_) {
ROCKS_LOG_ERROR(logger_, "Encounter unexpected blob index.");
status_ = Status::NotSupported(
"Encounter unexpected blob index. Please open DB with "
"rocksdb::blob_db::BlobDB instead.");
} else {
status_ =
Status::NotSupported("Blob DB does not support merge operator.");
}
valid_ = false;
return;
} else {
assert(false);
}
}
// 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.
s = MergeHelper::TimedFullMerge(merge_operator_, saved_key_.GetUserKey(),
nullptr, merge_context_.GetOperands(),
&saved_value_, logger_, statistics_, env_,
&pinned_value_, true);
if (!s.ok()) {
status_ = s;
}
}
void DBIter::Prev() {
assert(valid_);
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
if (direction_ == kForward) {
ReverseToBackward();
}
PrevInternal();
if (statistics_ != nullptr) {
local_stats_.prev_count_++;
if (valid_) {
local_stats_.prev_found_count_++;
local_stats_.bytes_read_ += (key().size() + value().size());
}
}
}
void DBIter::ReverseToForward() {
if (prefix_extractor_ != nullptr && !total_order_seek_) {
IterKey last_key;
last_key.SetInternalKey(ParsedInternalKey(
saved_key_.GetUserKey(), kMaxSequenceNumber, kValueTypeForSeek));
iter_->Seek(last_key.GetInternalKey());
}
FindNextUserKey();
direction_ = kForward;
if (!iter_->Valid()) {
iter_->SeekToFirst();
range_del_agg_.InvalidateTombstoneMapPositions();
}
}
void DBIter::ReverseToBackward() {
if (prefix_extractor_ != nullptr && !total_order_seek_) {
IterKey last_key;
last_key.SetInternalKey(ParsedInternalKey(saved_key_.GetUserKey(), 0,
kValueTypeForSeekForPrev));
iter_->SeekForPrev(last_key.GetInternalKey());
}
if (current_entry_is_merged_) {
// Not placed in the same key. Need to call Prev() until finding the
// previous key.
if (!iter_->Valid()) {
iter_->SeekToLast();
range_del_agg_.InvalidateTombstoneMapPositions();
}
ParsedInternalKey ikey;
FindParseableKey(&ikey, kReverse);
while (iter_->Valid() &&
user_comparator_->Compare(ikey.user_key, saved_key_.GetUserKey()) >
0) {
assert(ikey.sequence != kMaxSequenceNumber);
if (!IsVisible(ikey.sequence)) {
PERF_COUNTER_ADD(internal_recent_skipped_count, 1);
} else {
PERF_COUNTER_ADD(internal_key_skipped_count, 1);
}
iter_->Prev();
FindParseableKey(&ikey, kReverse);
}
}
#ifndef NDEBUG
if (iter_->Valid()) {
ParsedInternalKey ikey;
assert(ParseKey(&ikey));
assert(user_comparator_->Compare(ikey.user_key, saved_key_.GetUserKey()) <=
0);
}
#endif
FindPrevUserKey();
direction_ = kReverse;
}
void DBIter::PrevInternal() {
if (!iter_->Valid()) {
valid_ = false;
return;
}
ParsedInternalKey ikey;
while (iter_->Valid()) {
saved_key_.SetUserKey(
ExtractUserKey(iter_->key()),
!iter_->IsKeyPinned() || !pin_thru_lifetime_ /* copy */);
if (prefix_extractor_ && prefix_same_as_start_ &&
prefix_extractor_->Transform(saved_key_.GetUserKey())
.compare(prefix_start_key_) != 0) {
// Current key does not have the same prefix as start
valid_ = false;
return;
}
if (iterate_lower_bound_ != nullptr &&
user_comparator_->Compare(saved_key_.GetUserKey(),
*iterate_lower_bound_) < 0) {
// We've iterated earlier than the user-specified lower bound.
valid_ = false;
return;
}
if (FindValueForCurrentKey()) {
if (!iter_->Valid()) {
return;
}
FindParseableKey(&ikey, kReverse);
if (user_comparator_->Equal(ikey.user_key, saved_key_.GetUserKey())) {
FindPrevUserKey();
}
return;
}
if (TooManyInternalKeysSkipped(false)) {
return;
}
if (!iter_->Valid()) {
break;
}
FindParseableKey(&ikey, kReverse);
if (user_comparator_->Equal(ikey.user_key, saved_key_.GetUserKey())) {
FindPrevUserKey();
}
}
// We haven't found any key - iterator is not valid
// Or the prefix is different than start prefix
assert(!iter_->Valid());
valid_ = false;
}
// This function checks, if the entry with biggest sequence_number <= sequence_
// is non kTypeDeletion or kTypeSingleDeletion. If it's not, we save value in
// saved_value_
bool DBIter::FindValueForCurrentKey() {
assert(iter_->Valid());
merge_context_.Clear();
current_entry_is_merged_ = false;
// last entry before merge (could be kTypeDeletion, kTypeSingleDeletion or
// kTypeValue)
ValueType last_not_merge_type = kTypeDeletion;
ValueType last_key_entry_type = kTypeDeletion;
ParsedInternalKey ikey;
FindParseableKey(&ikey, kReverse);
// Temporarily pin blocks that hold (merge operands / the value)
ReleaseTempPinnedData();
TempPinData();
size_t num_skipped = 0;
while (iter_->Valid() && IsVisible(ikey.sequence) &&
user_comparator_->Equal(ikey.user_key, saved_key_.GetUserKey())) {
if (TooManyInternalKeysSkipped()) {
return false;
}
// 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:
case kTypeBlobIndex:
if (range_del_agg_.ShouldDelete(
ikey,
RangeDelAggregator::RangePositioningMode::kBackwardTraversal)) {
last_key_entry_type = kTypeRangeDeletion;
PERF_COUNTER_ADD(internal_delete_skipped_count, 1);
} else {
assert(iter_->IsValuePinned());
pinned_value_ = iter_->value();
}
merge_context_.Clear();
last_not_merge_type = last_key_entry_type;
break;
case kTypeDeletion:
case kTypeSingleDeletion:
merge_context_.Clear();
last_not_merge_type = last_key_entry_type;
PERF_COUNTER_ADD(internal_delete_skipped_count, 1);
break;
case kTypeMerge:
if (range_del_agg_.ShouldDelete(
ikey,
RangeDelAggregator::RangePositioningMode::kBackwardTraversal)) {
merge_context_.Clear();
last_key_entry_type = kTypeRangeDeletion;
last_not_merge_type = last_key_entry_type;
PERF_COUNTER_ADD(internal_delete_skipped_count, 1);
} else {
assert(merge_operator_ != nullptr);
merge_context_.PushOperandBack(
iter_->value(), iter_->IsValuePinned() /* operand_pinned */);
PERF_COUNTER_ADD(internal_merge_count, 1);
}
break;
default:
assert(false);
}
PERF_COUNTER_ADD(internal_key_skipped_count, 1);
assert(user_comparator_->Equal(ikey.user_key, saved_key_.GetUserKey()));
iter_->Prev();
++num_skipped;
FindParseableKey(&ikey, kReverse);
}
Status s;
is_blob_ = false;
switch (last_key_entry_type) {
case kTypeDeletion:
case kTypeSingleDeletion:
case kTypeRangeDeletion:
valid_ = false;
return false;
case kTypeMerge:
current_entry_is_merged_ = true;
if (last_not_merge_type == kTypeDeletion ||
last_not_merge_type == kTypeSingleDeletion ||
last_not_merge_type == kTypeRangeDeletion) {
s = MergeHelper::TimedFullMerge(
merge_operator_, saved_key_.GetUserKey(), nullptr,
merge_context_.GetOperands(), &saved_value_, logger_, statistics_,
env_, &pinned_value_, true);
} else if (last_not_merge_type == kTypeBlobIndex) {
if (!allow_blob_) {
ROCKS_LOG_ERROR(logger_, "Encounter unexpected blob index.");
status_ = Status::NotSupported(
"Encounter unexpected blob index. Please open DB with "
"rocksdb::blob_db::BlobDB instead.");
} else {
status_ =
Status::NotSupported("Blob DB does not support merge operator.");
}
valid_ = false;
return true;
} else {
assert(last_not_merge_type == kTypeValue);
s = MergeHelper::TimedFullMerge(
merge_operator_, saved_key_.GetUserKey(), &pinned_value_,
merge_context_.GetOperands(), &saved_value_, logger_, statistics_,
env_, &pinned_value_, true);
}
break;
case kTypeValue:
// do nothing - we've already has value in saved_value_
break;
case kTypeBlobIndex:
if (!allow_blob_) {
ROCKS_LOG_ERROR(logger_, "Encounter unexpected blob index.");
status_ = Status::NotSupported(
"Encounter unexpected blob index. Please open DB with "
"rocksdb::blob_db::BlobDB instead.");
valid_ = false;
return true;
}
is_blob_ = true;
break;
default:
assert(false);
break;
}
valid_ = true;
if (!s.ok()) {
status_ = s;
}
return true;
}
// This function is used in FindValueForCurrentKey.
// We use Seek() function instead of Prev() to find necessary value
bool DBIter::FindValueForCurrentKeyUsingSeek() {
// FindValueForCurrentKey will enable pinning before calling
// FindValueForCurrentKeyUsingSeek()
assert(pinned_iters_mgr_.PinningEnabled());
std::string last_key;
AppendInternalKey(&last_key, ParsedInternalKey(saved_key_.GetUserKey(),
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 == kTypeDeletion || ikey.type == kTypeSingleDeletion ||
range_del_agg_.ShouldDelete(
ikey, RangeDelAggregator::RangePositioningMode::kBackwardTraversal)) {
valid_ = false;
return false;
}
if (ikey.type == kTypeBlobIndex && !allow_blob_) {
ROCKS_LOG_ERROR(logger_, "Encounter unexpected blob index.");
status_ = Status::NotSupported(
"Encounter unexpected blob index. Please open DB with "
"rocksdb::blob_db::BlobDB instead.");
valid_ = false;
return true;
}
if (ikey.type == kTypeValue || ikey.type == kTypeBlobIndex) {
assert(iter_->IsValuePinned());
pinned_value_ = iter_->value();
valid_ = true;
return true;
}
// kTypeMerge. We need to collect all kTypeMerge values and save them
// in operands
current_entry_is_merged_ = true;
merge_context_.Clear();
while (
iter_->Valid() &&
user_comparator_->Equal(ikey.user_key, saved_key_.GetUserKey()) &&
ikey.type == kTypeMerge &&
!range_del_agg_.ShouldDelete(
ikey, RangeDelAggregator::RangePositioningMode::kBackwardTraversal)) {
merge_context_.PushOperand(iter_->value(),
iter_->IsValuePinned() /* operand_pinned */);
PERF_COUNTER_ADD(internal_merge_count, 1);
iter_->Next();
FindParseableKey(&ikey, kForward);
}
Status s;
if (!iter_->Valid() ||
!user_comparator_->Equal(ikey.user_key, saved_key_.GetUserKey()) ||
ikey.type == kTypeDeletion || ikey.type == kTypeSingleDeletion ||
range_del_agg_.ShouldDelete(
ikey, RangeDelAggregator::RangePositioningMode::kBackwardTraversal)) {
s = MergeHelper::TimedFullMerge(merge_operator_, saved_key_.GetUserKey(),
nullptr, merge_context_.GetOperands(),
&saved_value_, logger_, statistics_, env_,
&pinned_value_, true);
// Make iter_ valid and point to saved_key_
if (!iter_->Valid() ||
!user_comparator_->Equal(ikey.user_key, saved_key_.GetUserKey())) {
iter_->Seek(last_key);
RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION);
}
valid_ = true;
if (!s.ok()) {
status_ = s;
}
return true;
}
const Slice& val = iter_->value();
s = MergeHelper::TimedFullMerge(merge_operator_, saved_key_.GetUserKey(),
&val, merge_context_.GetOperands(),
&saved_value_, logger_, statistics_, env_,
&pinned_value_, true);
valid_ = true;
if (!s.ok()) {
status_ = s;
}
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_->Equal(ikey.user_key, saved_key_.GetUserKey())) {
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);
int cmp;
while (iter_->Valid() &&
((cmp = user_comparator_->Compare(ikey.user_key,
saved_key_.GetUserKey())) == 0 ||
(cmp > 0 && !IsVisible(ikey.sequence)))) {
if (TooManyInternalKeysSkipped()) {
return;
}
if (cmp == 0) {
if (num_skipped >= max_skip_) {
num_skipped = 0;
IterKey last_key;
last_key.SetInternalKey(ParsedInternalKey(
saved_key_.GetUserKey(), kMaxSequenceNumber, kValueTypeForSeek));
iter_->Seek(last_key.GetInternalKey());
RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION);
} else {
++num_skipped;
}
}
assert(ikey.sequence != kMaxSequenceNumber);
if (!IsVisible(ikey.sequence)) {
PERF_COUNTER_ADD(internal_recent_skipped_count, 1);
} else {
PERF_COUNTER_ADD(internal_key_skipped_count, 1);
}
iter_->Prev();
FindParseableKey(&ikey, kReverse);
}
}
bool DBIter::TooManyInternalKeysSkipped(bool increment) {
if ((max_skippable_internal_keys_ > 0) &&
(num_internal_keys_skipped_ > max_skippable_internal_keys_)) {
valid_ = false;
status_ = Status::Incomplete("Too many internal keys skipped.");
return true;
} else if (increment) {
num_internal_keys_skipped_++;
}
return false;
}
bool DBIter::IsVisible(SequenceNumber sequence) {
return sequence <= sequence_ &&
(read_callback_ == nullptr || read_callback_->IsCommitted(sequence));
}
// 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);
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
saved_key_.Clear();
saved_key_.SetInternalKey(target, sequence_);
{
PERF_TIMER_GUARD(seek_internal_seek_time);
iter_->Seek(saved_key_.GetInternalKey());
range_del_agg_.InvalidateTombstoneMapPositions();
}
RecordTick(statistics_, NUMBER_DB_SEEK);
if (iter_->Valid()) {
if (prefix_extractor_ && prefix_same_as_start_) {
prefix_start_key_ = prefix_extractor_->Transform(target);
}
direction_ = kForward;
ClearSavedValue();
FindNextUserEntry(false /* not skipping */, prefix_same_as_start_);
if (!valid_) {
prefix_start_key_.clear();
}
if (statistics_ != nullptr) {
if (valid_) {
// Decrement since we don't want to count this key as skipped
RecordTick(statistics_, NUMBER_DB_SEEK_FOUND);
RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size());
}
}
} else {
valid_ = false;
}
if (valid_ && prefix_extractor_ && prefix_same_as_start_) {
prefix_start_buf_.SetUserKey(prefix_start_key_);
prefix_start_key_ = prefix_start_buf_.GetUserKey();
}
}
void DBIter::SeekForPrev(const Slice& target) {
StopWatch sw(env_, statistics_, DB_SEEK);
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
saved_key_.Clear();
// now saved_key is used to store internal key.
saved_key_.SetInternalKey(target, 0 /* sequence_number */,
kValueTypeForSeekForPrev);
{
PERF_TIMER_GUARD(seek_internal_seek_time);
iter_->SeekForPrev(saved_key_.GetInternalKey());
range_del_agg_.InvalidateTombstoneMapPositions();
}
RecordTick(statistics_, NUMBER_DB_SEEK);
if (iter_->Valid()) {
if (prefix_extractor_ && prefix_same_as_start_) {
prefix_start_key_ = prefix_extractor_->Transform(target);
}
direction_ = kReverse;
ClearSavedValue();
PrevInternal();
if (!valid_) {
prefix_start_key_.clear();
}
if (statistics_ != nullptr) {
if (valid_) {
RecordTick(statistics_, NUMBER_DB_SEEK_FOUND);
RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size());
}
}
} else {
valid_ = false;
}
if (valid_ && prefix_extractor_ && prefix_same_as_start_) {
prefix_start_buf_.SetUserKey(prefix_start_key_);
prefix_start_key_ = prefix_start_buf_.GetUserKey();
}
}
void DBIter::SeekToFirst() {
// Don't use iter_::Seek() if we set a prefix extractor
// because prefix seek will be used.
if (prefix_extractor_ != nullptr) {
max_skip_ = std::numeric_limits<uint64_t>::max();
}
if (iterate_lower_bound_ != nullptr) {
Seek(*iterate_lower_bound_);
return;
}
direction_ = kForward;
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
ClearSavedValue();
{
PERF_TIMER_GUARD(seek_internal_seek_time);
iter_->SeekToFirst();
range_del_agg_.InvalidateTombstoneMapPositions();
}
RecordTick(statistics_, NUMBER_DB_SEEK);
if (iter_->Valid()) {
saved_key_.SetUserKey(
ExtractUserKey(iter_->key()),
!iter_->IsKeyPinned() || !pin_thru_lifetime_ /* copy */);
FindNextUserEntry(false /* not skipping */, false /* no prefix check */);
if (statistics_ != nullptr) {
if (valid_) {
RecordTick(statistics_, NUMBER_DB_SEEK_FOUND);
RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size());
}
}
} else {
valid_ = false;
}
if (valid_ && prefix_extractor_ && prefix_same_as_start_) {
prefix_start_buf_.SetUserKey(
prefix_extractor_->Transform(saved_key_.GetUserKey()));
prefix_start_key_ = prefix_start_buf_.GetUserKey();
}
}
void DBIter::SeekToLast() {
// Don't use iter_::Seek() if we set a prefix extractor
// because prefix seek will be used.
if (prefix_extractor_ != nullptr) {
max_skip_ = std::numeric_limits<uint64_t>::max();
}
direction_ = kReverse;
ReleaseTempPinnedData();
ResetInternalKeysSkippedCounter();
ClearSavedValue();
{
PERF_TIMER_GUARD(seek_internal_seek_time);
iter_->SeekToLast();
range_del_agg_.InvalidateTombstoneMapPositions();
}
// When the iterate_upper_bound is set to a value,
// it will seek to the last key before the
// ReadOptions.iterate_upper_bound
if (iter_->Valid() && iterate_upper_bound_ != nullptr) {
SeekForPrev(*iterate_upper_bound_);
range_del_agg_.InvalidateTombstoneMapPositions();
if (!Valid()) {
return;
} else if (user_comparator_->Equal(*iterate_upper_bound_, key())) {
ReleaseTempPinnedData();
PrevInternal();
}
} else {
PrevInternal();
}
if (statistics_ != nullptr) {
RecordTick(statistics_, NUMBER_DB_SEEK);
if (valid_) {
RecordTick(statistics_, NUMBER_DB_SEEK_FOUND);
RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size());
}
}
if (valid_ && prefix_extractor_ && prefix_same_as_start_) {
prefix_start_buf_.SetUserKey(
prefix_extractor_->Transform(saved_key_.GetUserKey()));
prefix_start_key_ = prefix_start_buf_.GetUserKey();
}
}
Iterator* NewDBIterator(Env* env, const ReadOptions& read_options,
const ImmutableCFOptions& cf_options,
const Comparator* user_key_comparator,
InternalIterator* internal_iter,
const SequenceNumber& sequence,
uint64_t max_sequential_skip_in_iterations,
ReadCallback* read_callback, bool allow_blob) {
DBIter* db_iter =
new DBIter(env, read_options, cf_options, user_key_comparator,
internal_iter, sequence, false,
max_sequential_skip_in_iterations, read_callback, allow_blob);
return db_iter;
}
ArenaWrappedDBIter::~ArenaWrappedDBIter() { db_iter_->~DBIter(); }
RangeDelAggregator* ArenaWrappedDBIter::GetRangeDelAggregator() {
return db_iter_->GetRangeDelAggregator();
}
void ArenaWrappedDBIter::SetIterUnderDBIter(InternalIterator* 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::SeekForPrev(const Slice& target) {
db_iter_->SeekForPrev(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(); }
bool ArenaWrappedDBIter::IsBlob() const { return db_iter_->IsBlob(); }
inline Status ArenaWrappedDBIter::GetProperty(std::string prop_name,
std::string* prop) {
if (prop_name == "rocksdb.iterator.super-version-number") {
// First try to pass the value returned from inner iterator.
if (!db_iter_->GetProperty(prop_name, prop).ok()) {
*prop = ToString(sv_number_);
}
return Status::OK();
}
return db_iter_->GetProperty(prop_name, prop);
}
void ArenaWrappedDBIter::Init(Env* env, const ReadOptions& read_options,
const ImmutableCFOptions& cf_options,
const SequenceNumber& sequence,
uint64_t max_sequential_skip_in_iteration,
uint64_t version_number,
ReadCallback* read_callback, bool allow_blob) {
auto mem = arena_.AllocateAligned(sizeof(DBIter));
db_iter_ = new (mem)
DBIter(env, read_options, cf_options, cf_options.user_comparator, nullptr,
sequence, true, max_sequential_skip_in_iteration, read_callback,
allow_blob);
sv_number_ = version_number;
}
Status ArenaWrappedDBIter::Refresh() {
if (cfd_ == nullptr || db_impl_ == nullptr) {
return Status::NotSupported("Creating renew iterator is not allowed.");
}
assert(db_iter_ != nullptr);
// TODO(yiwu): For allocate_seq_only_for_data_==false, this is not the correct
// behavior. Will be corrected automatically when we take a snapshot here for
// the case of WritePreparedTxnDB.
SequenceNumber latest_seq = db_impl_->GetLatestSequenceNumber();
uint64_t cur_sv_number = cfd_->GetSuperVersionNumber();
if (sv_number_ != cur_sv_number) {
Env* env = db_iter_->env();
db_iter_->~DBIter();
arena_.~Arena();
new (&arena_) Arena();
SuperVersion* sv = cfd_->GetReferencedSuperVersion(db_impl_->mutex());
Init(env, read_options_, *(cfd_->ioptions()), latest_seq,
sv->mutable_cf_options.max_sequential_skip_in_iterations,
cur_sv_number, read_callback_, allow_blob_);
InternalIterator* internal_iter = db_impl_->NewInternalIterator(
read_options_, cfd_, sv, &arena_, db_iter_->GetRangeDelAggregator());
SetIterUnderDBIter(internal_iter);
} else {
db_iter_->set_sequence(latest_seq);
db_iter_->set_valid(false);
}
return Status::OK();
}
ArenaWrappedDBIter* NewArenaWrappedDbIterator(
Env* env, const ReadOptions& read_options,
const ImmutableCFOptions& cf_options, const SequenceNumber& sequence,
uint64_t max_sequential_skip_in_iterations, uint64_t version_number,
ReadCallback* read_callback, DBImpl* db_impl, ColumnFamilyData* cfd,
bool allow_blob) {
ArenaWrappedDBIter* iter = new ArenaWrappedDBIter();
iter->Init(env, read_options, cf_options, sequence,
max_sequential_skip_in_iterations, version_number, read_callback,
allow_blob);
if (db_impl != nullptr && cfd != nullptr) {
iter->StoreRefreshInfo(read_options, db_impl, cfd, read_callback,
allow_blob);
}
return iter;
}
} // namespace rocksdb
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