rocksdb/db/forward_iterator.cc
Tomislav Novak 3b97ee96c4 ForwardIterator seek bugfix
Summary:
If `NeedToSeekImmutable()` returns false, `SeekInternal()` won't reset the
contents of `immutable_min_heap_`. However, since it calls `UpdateCurrent()`
unconditionally, if `current_` is one of immutable iterators (previously popped
from `immutable_min_heap_`), `UpdateCurrent()` will overwrite it. As a result,
if old `current_` in fact pointed to the smallest entry, forward iterator will
skip some records.

Fix implemented in this diff pushes `current_` back to `immutable_min_heap_`
before calling `UpdateCurrent()`.

Test Plan:
New unit test (courtesy of @lovro):
   $ ROCKSDB_TESTS=TailingIteratorSeekToSame ./db_test

Reviewers: igor, dhruba, haobo, ljin

Reviewed By: ljin

Subscribers: lovro, leveldb

Differential Revision: https://reviews.facebook.net/D19653
2014-07-10 16:46:13 -07:00

464 lines
13 KiB
C++

// 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.
#ifndef ROCKSDB_LITE
#include "db/forward_iterator.h"
#include <string>
#include <utility>
#include <limits>
#include "db/db_impl.h"
#include "db/db_iter.h"
#include "db/column_family.h"
#include "rocksdb/env.h"
#include "rocksdb/slice.h"
#include "rocksdb/slice_transform.h"
#include "table/merger.h"
#include "db/dbformat.h"
namespace rocksdb {
// Usage:
// LevelIterator iter;
// iter.SetFileIndex(file_index);
// iter.Seek(target);
// iter.Next()
class LevelIterator : public Iterator {
public:
LevelIterator(const ColumnFamilyData* const cfd,
const ReadOptions& read_options,
const std::vector<FileMetaData*>& files)
: cfd_(cfd), read_options_(read_options), files_(files), valid_(false),
file_index_(std::numeric_limits<uint32_t>::max()) {}
void SetFileIndex(uint32_t file_index) {
assert(file_index < files_.size());
if (file_index != file_index_) {
file_index_ = file_index;
file_iter_.reset(cfd_->table_cache()->NewIterator(
read_options_, *(cfd_->soptions()), cfd_->internal_comparator(),
files_[file_index_]->fd, nullptr /* table_reader_ptr */, false));
}
valid_ = false;
}
void SeekToLast() override {
status_ = Status::NotSupported("LevelIterator::SeekToLast()");
valid_ = false;
}
void Prev() {
status_ = Status::NotSupported("LevelIterator::Prev()");
valid_ = false;
}
bool Valid() const override {
return valid_;
}
void SeekToFirst() override {
SetFileIndex(0);
file_iter_->SeekToFirst();
valid_ = file_iter_->Valid();
}
void Seek(const Slice& internal_key) override {
assert(file_iter_ != nullptr);
file_iter_->Seek(internal_key);
valid_ = file_iter_->Valid();
assert(valid_);
}
void Next() override {
assert(valid_);
file_iter_->Next();
while (!file_iter_->Valid()) {
if (file_index_ + 1 >= files_.size()) {
valid_ = false;
return;
}
SetFileIndex(file_index_ + 1);
file_iter_->SeekToFirst();
}
valid_ = file_iter_->Valid();
}
Slice key() const override {
assert(valid_);
return file_iter_->key();
}
Slice value() const override {
assert(valid_);
return file_iter_->value();
}
Status status() const override {
if (!status_.ok()) {
return status_;
} else if (file_iter_ && !file_iter_->status().ok()) {
return file_iter_->status();
}
return Status::OK();
}
private:
const ColumnFamilyData* const cfd_;
const ReadOptions& read_options_;
const std::vector<FileMetaData*>& files_;
bool valid_;
uint32_t file_index_;
Status status_;
std::unique_ptr<Iterator> file_iter_;
};
ForwardIterator::ForwardIterator(DBImpl* db, const ReadOptions& read_options,
ColumnFamilyData* cfd)
: db_(db),
read_options_(read_options),
cfd_(cfd),
prefix_extractor_(cfd->options()->prefix_extractor.get()),
user_comparator_(cfd->user_comparator()),
immutable_min_heap_(MinIterComparator(&cfd_->internal_comparator())),
sv_(nullptr),
mutable_iter_(nullptr),
current_(nullptr),
valid_(false),
is_prev_set_(false) {}
ForwardIterator::~ForwardIterator() {
Cleanup();
}
void ForwardIterator::Cleanup() {
delete mutable_iter_;
for (auto* m : imm_iters_) {
delete m;
}
imm_iters_.clear();
for (auto* f : l0_iters_) {
delete f;
}
l0_iters_.clear();
for (auto* l : level_iters_) {
delete l;
}
level_iters_.clear();
if (sv_ != nullptr && sv_->Unref()) {
DBImpl::DeletionState deletion_state;
db_->mutex_.Lock();
sv_->Cleanup();
db_->FindObsoleteFiles(deletion_state, false, true);
db_->mutex_.Unlock();
delete sv_;
if (deletion_state.HaveSomethingToDelete()) {
db_->PurgeObsoleteFiles(deletion_state);
}
}
}
bool ForwardIterator::Valid() const {
return valid_;
}
void ForwardIterator::SeekToFirst() {
if (sv_ == nullptr ||
sv_ ->version_number != cfd_->GetSuperVersionNumber()) {
RebuildIterators();
}
SeekInternal(Slice(), true);
}
void ForwardIterator::Seek(const Slice& internal_key) {
if (sv_ == nullptr ||
sv_ ->version_number != cfd_->GetSuperVersionNumber()) {
RebuildIterators();
}
SeekInternal(internal_key, false);
}
void ForwardIterator::SeekInternal(const Slice& internal_key,
bool seek_to_first) {
// mutable
seek_to_first ? mutable_iter_->SeekToFirst() :
mutable_iter_->Seek(internal_key);
// immutable
// TODO(ljin): NeedToSeekImmutable has negative impact on performance
// if it turns to need to seek immutable often. We probably want to have
// an option to turn it off.
if (seek_to_first || NeedToSeekImmutable(internal_key)) {
{
auto tmp = MinIterHeap(MinIterComparator(&cfd_->internal_comparator()));
immutable_min_heap_.swap(tmp);
}
for (auto* m : imm_iters_) {
seek_to_first ? m->SeekToFirst() : m->Seek(internal_key);
if (m->Valid()) {
immutable_min_heap_.push(m);
}
}
Slice user_key;
if (!seek_to_first) {
user_key = ExtractUserKey(internal_key);
}
auto* files = sv_->current->files_;
for (uint32_t i = 0; i < files[0].size(); ++i) {
if (seek_to_first) {
l0_iters_[i]->SeekToFirst();
} else {
// If the target key passes over the larget key, we are sure Next()
// won't go over this file.
if (user_comparator_->Compare(user_key,
files[0][i]->largest.user_key()) > 0) {
continue;
}
l0_iters_[i]->Seek(internal_key);
}
if (l0_iters_[i]->Valid()) {
immutable_min_heap_.push(l0_iters_[i]);
}
}
int32_t search_left_bound = 0;
int32_t search_right_bound = FileIndexer::kLevelMaxIndex;
for (int32_t level = 1; level < sv_->current->NumberLevels(); ++level) {
if (files[level].empty()) {
search_left_bound = 0;
search_right_bound = FileIndexer::kLevelMaxIndex;
continue;
}
assert(level_iters_[level - 1] != nullptr);
uint32_t f_idx = 0;
if (!seek_to_first) {
// TODO(ljin): remove before committing
// f_idx = FindFileInRange(
// files[level], internal_key, 0, files[level].size());
if (search_left_bound == search_right_bound) {
f_idx = search_left_bound;
} else if (search_left_bound < search_right_bound) {
f_idx = FindFileInRange(
files[level], internal_key, search_left_bound,
search_right_bound == FileIndexer::kLevelMaxIndex ?
files[level].size() : search_right_bound);
} else {
// search_left_bound > search_right_bound
// There are only 2 cases this can happen:
// (1) target key is smaller than left most file
// (2) target key is larger than right most file
assert(search_left_bound == (int32_t)files[level].size() ||
search_right_bound == -1);
if (search_right_bound == -1) {
assert(search_left_bound == 0);
f_idx = 0;
} else {
sv_->current->file_indexer_.GetNextLevelIndex(
level, files[level].size() - 1,
1, 1, &search_left_bound, &search_right_bound);
continue;
}
}
// Prepare hints for the next level
if (f_idx < files[level].size()) {
int cmp_smallest = user_comparator_->Compare(
user_key, files[level][f_idx]->smallest.user_key());
int cmp_largest = -1;
if (cmp_smallest >= 0) {
cmp_smallest = user_comparator_->Compare(
user_key, files[level][f_idx]->smallest.user_key());
}
sv_->current->file_indexer_.GetNextLevelIndex(level, f_idx,
cmp_smallest, cmp_largest,
&search_left_bound, &search_right_bound);
} else {
sv_->current->file_indexer_.GetNextLevelIndex(
level, files[level].size() - 1,
1, 1, &search_left_bound, &search_right_bound);
}
}
// Seek
if (f_idx < files[level].size()) {
level_iters_[level - 1]->SetFileIndex(f_idx);
seek_to_first ? level_iters_[level - 1]->SeekToFirst() :
level_iters_[level - 1]->Seek(internal_key);
if (level_iters_[level - 1]->Valid()) {
immutable_min_heap_.push(level_iters_[level - 1]);
}
}
}
if (seek_to_first || immutable_min_heap_.empty()) {
is_prev_set_ = false;
} else {
prev_key_.SetKey(internal_key);
is_prev_set_ = true;
}
} else if (current_ && current_ != mutable_iter_) {
// current_ is one of immutable iterators, push it back to the heap
immutable_min_heap_.push(current_);
}
UpdateCurrent();
}
void ForwardIterator::Next() {
assert(valid_);
if (sv_ == nullptr ||
sv_ ->version_number != cfd_->GetSuperVersionNumber()) {
std::string current_key = key().ToString();
Slice old_key(current_key.data(), current_key.size());
RebuildIterators();
SeekInternal(old_key, false);
if (!valid_ || key().compare(old_key) != 0) {
return;
}
} else if (current_ != mutable_iter_) {
// It is going to advance immutable iterator
prev_key_.SetKey(current_->key());
is_prev_set_ = true;
}
current_->Next();
if (current_->Valid() && current_ != mutable_iter_) {
immutable_min_heap_.push(current_);
}
UpdateCurrent();
}
Slice ForwardIterator::key() const {
assert(valid_);
return current_->key();
}
Slice ForwardIterator::value() const {
assert(valid_);
return current_->value();
}
Status ForwardIterator::status() const {
if (!status_.ok()) {
return status_;
} else if (!mutable_iter_->status().ok()) {
return mutable_iter_->status();
}
for (auto *it : imm_iters_) {
if (it && !it->status().ok()) {
return it->status();
}
}
for (auto *it : l0_iters_) {
if (it && !it->status().ok()) {
return it->status();
}
}
for (auto *it : level_iters_) {
if (it && !it->status().ok()) {
return it->status();
}
}
return Status::OK();
}
void ForwardIterator::RebuildIterators() {
// Clean up
Cleanup();
// New
sv_ = cfd_->GetReferencedSuperVersion(&(db_->mutex_));
mutable_iter_ = sv_->mem->NewIterator(read_options_);
sv_->imm->AddIterators(read_options_, &imm_iters_);
const auto& l0_files = sv_->current->files_[0];
l0_iters_.reserve(l0_files.size());
for (const auto* l0 : l0_files) {
l0_iters_.push_back(cfd_->table_cache()->NewIterator(
read_options_, *cfd_->soptions(), cfd_->internal_comparator(), l0->fd));
}
level_iters_.reserve(sv_->current->NumberLevels() - 1);
for (int32_t level = 1; level < sv_->current->NumberLevels(); ++level) {
if (sv_->current->files_[level].empty()) {
level_iters_.push_back(nullptr);
} else {
level_iters_.push_back(new LevelIterator(cfd_, read_options_,
sv_->current->files_[level]));
}
}
current_ = nullptr;
is_prev_set_ = false;
}
void ForwardIterator::UpdateCurrent() {
if (immutable_min_heap_.empty() && !mutable_iter_->Valid()) {
current_ = nullptr;
} else if (immutable_min_heap_.empty()) {
current_ = mutable_iter_;
} else if (!mutable_iter_->Valid()) {
current_ = immutable_min_heap_.top();
immutable_min_heap_.pop();
} else {
current_ = immutable_min_heap_.top();
assert(current_ != nullptr);
assert(current_->Valid());
int cmp = cfd_->internal_comparator().InternalKeyComparator::Compare(
mutable_iter_->key(), current_->key());
assert(cmp != 0);
if (cmp > 0) {
immutable_min_heap_.pop();
} else {
current_ = mutable_iter_;
}
}
valid_ = (current_ != nullptr);
if (!status_.ok()) {
status_ = Status::OK();
}
}
bool ForwardIterator::NeedToSeekImmutable(const Slice& target) {
if (!is_prev_set_) {
return true;
}
Slice prev_key = prev_key_.GetKey();
if (prefix_extractor_ && prefix_extractor_->Transform(target).compare(
prefix_extractor_->Transform(prev_key)) != 0) {
return true;
}
if (cfd_->internal_comparator().InternalKeyComparator::Compare(
prev_key, target) >= 0) {
return true;
}
if (immutable_min_heap_.empty() ||
cfd_->internal_comparator().InternalKeyComparator::Compare(
target, current_ == mutable_iter_ ? immutable_min_heap_.top()->key()
: current_->key()) > 0) {
return true;
}
return false;
}
uint32_t ForwardIterator::FindFileInRange(
const std::vector<FileMetaData*>& files, const Slice& internal_key,
uint32_t left, uint32_t right) {
while (left < right) {
uint32_t mid = (left + right) / 2;
const FileMetaData* f = files[mid];
if (cfd_->internal_comparator().InternalKeyComparator::Compare(
f->largest.Encode(), internal_key) < 0) {
// Key at "mid.largest" is < "target". Therefore all
// files at or before "mid" are uninteresting.
left = mid + 1;
} else {
// Key at "mid.largest" is >= "target". Therefore all files
// after "mid" are uninteresting.
right = mid;
}
}
return right;
}
} // namespace rocksdb
#endif // ROCKSDB_LITE