Aggregate hot Iterator counters in LocalStatistics (DBIter::Next perf regression)
Summary:
This patch bump the counters in the frequent code path DBIter::Next() / DBIter::Prev() in a local data members and send them to Statistics when the iterator is destroyed
A better solution will be to have thread_local implementation for Statistics
New performance
```
readseq : 0.035 micros/op 28597881 ops/sec; 3163.7 MB/s
1,851,568,819 stalled-cycles-frontend # 31.29% frontend cycles idle [49.86%]
884,929,823 stalled-cycles-backend # 14.95% backend cycles idle [50.21%]
readreverse : 0.071 micros/op 14077393 ops/sec; 1557.3 MB/s
3,239,575,993 stalled-cycles-frontend # 27.36% frontend cycles idle [49.96%]
1,558,253,983 stalled-cycles-backend # 13.16% backend cycles idle [50.14%]
```
Existing performance
```
readreverse : 0.174 micros/op 5732342 ops/sec; 634.1 MB/s
20,570,209,389 stalled-cycles-frontend # 70.71% frontend cycles idle [50.01%]
18,422,816,837 stalled-cycles-backend # 63.33% backend cycles idle [50.04%]
readseq : 0.119 micros/op 8400537 ops/sec; 929.3 MB/s
15,634,225,844 stalled-cycles-frontend # 79.07% frontend cycles idle [49.96%]
14,227,427,453 stalled-cycles-backend # 71.95% backend cycles idle [50.09%]
```
Test Plan: unit tests
Reviewers: yhchiang, sdong, igor
Reviewed By: sdong
Subscribers: andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D55107
This commit is contained in:
Islam AbdelRahman
parent
790252805d
commit
580fede347
@ -3,6 +3,7 @@
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### Public API Changes
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* Change default of BlockBasedTableOptions.format_version to 2. It means default DB created by 4.6 or up cannot be opened by RocksDB version 3.9 or earlier.
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* Added strict_capacity_limit option to NewLRUCache. If the flag is set to true, insert to cache will fail if no enough capacity can be free. Signiture of Cache::Insert() is updated accordingly.
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* Tickers [NUMBER_DB_NEXT, NUMBER_DB_PREV, NUMBER_DB_NEXT_FOUND, NUMBER_DB_PREV_FOUND, ITER_BYTES_READ] are not updated immediately. The are updated when the Iterator is deleted.
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### New Features
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* Add CompactionPri::kMinOverlappingRatio, a compaction picking mode friendly to write amplification.
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* Deprecate Iterator::IsKeyPinned() and replace it with Iterator::GetProperty() with prop_name="rocksdb.iterator.is.key.pinned"
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@ -60,6 +60,44 @@ class DBIter: public Iterator {
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kReverse
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};
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// LocalStatistics contain Statistics counters that will be aggregated per
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// each iterator instance and then will be sent to the global statistics when
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// the iterator is destroyed.
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//
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// The purpose of this approach is to avoid perf regression happening
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// when multiple threads bump the atomic counters from a DBIter::Next().
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struct LocalStatistics {
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explicit LocalStatistics() { ResetCounters(); }
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void ResetCounters() {
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next_count_ = 0;
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next_found_count_ = 0;
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prev_count_ = 0;
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prev_found_count_ = 0;
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bytes_read_ = 0;
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}
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void BumpGlobalStatistics(Statistics* global_statistics) {
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RecordTick(global_statistics, NUMBER_DB_NEXT, next_count_);
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RecordTick(global_statistics, NUMBER_DB_NEXT_FOUND, next_found_count_);
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RecordTick(global_statistics, NUMBER_DB_PREV, prev_count_);
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RecordTick(global_statistics, NUMBER_DB_PREV_FOUND, prev_found_count_);
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RecordTick(global_statistics, ITER_BYTES_READ, bytes_read_);
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ResetCounters();
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}
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// Map to Tickers::NUMBER_DB_NEXT
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uint64_t next_count_;
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// Map to Tickers::NUMBER_DB_NEXT_FOUND
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uint64_t next_found_count_;
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// Map to Tickers::NUMBER_DB_PREV
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uint64_t prev_count_;
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// Map to Tickers::NUMBER_DB_PREV_FOUND
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uint64_t prev_found_count_;
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// Map to Tickers::ITER_BYTES_READ
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uint64_t bytes_read_;
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};
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DBIter(Env* env, const ImmutableCFOptions& ioptions, const Comparator* cmp,
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InternalIterator* iter, SequenceNumber s, bool arena_mode,
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uint64_t max_sequential_skip_in_iterations, uint64_t version_number,
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@ -86,6 +124,7 @@ class DBIter: public Iterator {
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}
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virtual ~DBIter() {
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RecordTick(statistics_, NO_ITERATORS, -1);
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local_stats_.BumpGlobalStatistics(statistics_);
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if (!arena_mode_) {
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delete iter_;
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} else {
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@ -213,6 +252,7 @@ class DBIter: public Iterator {
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bool iter_pinned_;
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// List of operands for merge operator.
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std::deque<std::string> merge_operands_;
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LocalStatistics local_stats_;
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// No copying allowed
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DBIter(const DBIter&);
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@ -250,6 +290,9 @@ void DBIter::Next() {
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PERF_COUNTER_ADD(internal_key_skipped_count, 1);
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}
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if (statistics_ != nullptr) {
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local_stats_.next_count_++;
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}
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// Now we point to the next internal position, for both of merge and
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// not merge cases.
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if (!iter_->Valid()) {
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@ -257,18 +300,15 @@ void DBIter::Next() {
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return;
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}
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FindNextUserEntry(true /* skipping the current user key */);
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if (statistics_ != nullptr) {
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RecordTick(statistics_, NUMBER_DB_NEXT);
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if (valid_) {
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RecordTick(statistics_, NUMBER_DB_NEXT_FOUND);
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RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
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}
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}
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if (valid_ && prefix_extractor_ && prefix_same_as_start_ &&
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prefix_extractor_->Transform(saved_key_.GetKey())
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.compare(prefix_start_.GetKey()) != 0) {
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valid_ = false;
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}
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if (statistics_ != nullptr && valid_) {
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local_stats_.next_found_count_++;
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local_stats_.bytes_read_ += (key().size() + value().size());
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}
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}
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// PRE: saved_key_ has the current user key if skipping
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@ -436,10 +476,10 @@ void DBIter::Prev() {
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}
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PrevInternal();
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if (statistics_ != nullptr) {
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RecordTick(statistics_, NUMBER_DB_PREV);
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local_stats_.prev_count_++;
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if (valid_) {
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RecordTick(statistics_, NUMBER_DB_PREV_FOUND);
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RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
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local_stats_.prev_found_count_++;
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local_stats_.bytes_read_ += (key().size() + value().size());
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}
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}
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if (valid_ && prefix_extractor_ && prefix_same_as_start_ &&
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@ -10611,6 +10611,88 @@ TEST_F(DBTest, PrefixExtractorBlockFilter) {
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delete iter;
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}
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TEST_F(DBTest, IteratorWithLocalStatistics) {
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Options options = CurrentOptions();
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options.statistics = rocksdb::CreateDBStatistics();
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DestroyAndReopen(options);
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Random rnd(301);
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for (int i = 0; i < 1000; i++) {
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// Key 10 bytes / Value 10 bytes
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ASSERT_OK(Put(RandomString(&rnd, 10), RandomString(&rnd, 10)));
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}
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std::atomic<uint64_t> total_next(0);
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std::atomic<uint64_t> total_next_found(0);
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std::atomic<uint64_t> total_prev(0);
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std::atomic<uint64_t> total_prev_found(0);
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std::atomic<uint64_t> total_bytes(0);
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std::vector<std::thread> threads;
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std::function<void()> reader_func_next = [&]() {
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Iterator* iter = db_->NewIterator(ReadOptions());
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iter->SeekToFirst();
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// Seek will bump ITER_BYTES_READ
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total_bytes += iter->key().size();
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total_bytes += iter->value().size();
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while (true) {
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iter->Next();
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total_next++;
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if (!iter->Valid()) {
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break;
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}
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total_next_found++;
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total_bytes += iter->key().size();
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total_bytes += iter->value().size();
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}
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delete iter;
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};
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std::function<void()> reader_func_prev = [&]() {
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Iterator* iter = db_->NewIterator(ReadOptions());
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iter->SeekToLast();
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// Seek will bump ITER_BYTES_READ
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total_bytes += iter->key().size();
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total_bytes += iter->value().size();
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while (true) {
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iter->Prev();
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total_prev++;
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if (!iter->Valid()) {
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break;
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}
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total_prev_found++;
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total_bytes += iter->key().size();
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total_bytes += iter->value().size();
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}
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delete iter;
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};
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for (int i = 0; i < 10; i++) {
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threads.emplace_back(reader_func_next);
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}
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for (int i = 0; i < 15; i++) {
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threads.emplace_back(reader_func_prev);
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}
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for (auto& t : threads) {
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t.join();
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}
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ASSERT_EQ(TestGetTickerCount(options, NUMBER_DB_NEXT), total_next);
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ASSERT_EQ(TestGetTickerCount(options, NUMBER_DB_NEXT_FOUND),
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total_next_found);
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ASSERT_EQ(TestGetTickerCount(options, NUMBER_DB_PREV), total_prev);
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ASSERT_EQ(TestGetTickerCount(options, NUMBER_DB_PREV_FOUND),
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total_prev_found);
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ASSERT_EQ(TestGetTickerCount(options, ITER_BYTES_READ), total_bytes);
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}
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#ifndef ROCKSDB_LITE
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class BloomStatsTestWithParam
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: public DBTest,
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