From 0418e66e2a7cb96924455b12032cdb954576f4ec Mon Sep 17 00:00:00 2001 From: Radheshyam Balasundaram Date: Wed, 16 Jul 2014 13:33:02 -0700 Subject: [PATCH] Refactoring Version::Get() Summary: Refactoring Version::Get() method to move file picker logic to a separate class. Test Plan: make check all Reviewers: igor, sdong, ljin Reviewed By: ljin Subscribers: leveldb Differential Revision: https://reviews.facebook.net/D19713 --- db/version_set.cc | 478 +++++++++++++++++++++++++++------------------- 1 file changed, 278 insertions(+), 200 deletions(-) diff --git a/db/version_set.cc b/db/version_set.cc index e2e08fdb3..62a52dcd7 100644 --- a/db/version_set.cc +++ b/db/version_set.cc @@ -40,6 +40,263 @@ namespace rocksdb { +namespace { + +// Find File in FileLevel data structure +// Within an index range defined by left and right +int FindFileInRange(const InternalKeyComparator& icmp, + const FileLevel& file_level, + const Slice& key, + uint32_t left, + uint32_t right) { + while (left < right) { + uint32_t mid = (left + right) / 2; + const FdWithKeyRange& f = file_level.files[mid]; + if (icmp.InternalKeyComparator::Compare(f.largest_key, 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; +} + +bool NewestFirstBySeqNo(FileMetaData* a, FileMetaData* b) { + if (a->smallest_seqno != b->smallest_seqno) { + return a->smallest_seqno > b->smallest_seqno; + } + if (a->largest_seqno != b->largest_seqno) { + return a->largest_seqno > b->largest_seqno; + } + // Break ties by file number + return a->fd.GetNumber() > b->fd.GetNumber(); +} + +bool BySmallestKey(FileMetaData* a, FileMetaData* b, + const InternalKeyComparator* cmp) { + int r = cmp->Compare(a->smallest, b->smallest); + if (r != 0) { + return (r < 0); + } + // Break ties by file number + return (a->fd.GetNumber() < b->fd.GetNumber()); +} + +// Class to help choose the next file to search for the particular key. +// Searches and returns files level by level. +// We can search level-by-level since entries never hop across +// levels. Therefore we are guaranteed that if we find data +// in a smaller level, later levels are irrelevant (unless we +// are MergeInProgress). +class FilePicker { + public: + FilePicker( + std::vector* files, + const Slice& user_key, + const Slice& ikey, + autovector* file_levels, + unsigned int num_levels, + FileIndexer* file_indexer, + const Comparator* user_comparator, + const InternalKeyComparator* internal_comparator) + : num_levels_(num_levels), + curr_level_(-1), + search_left_bound_(0), + search_right_bound_(FileIndexer::kLevelMaxIndex), + files_(files), + file_levels_(file_levels), + user_key_(user_key), + ikey_(ikey), + file_indexer_(file_indexer), + user_comparator_(user_comparator), + internal_comparator_(internal_comparator) { + // Setup member variables to search first level. + search_ended_ = !PrepareNextLevel(); + if (!search_ended_) { + // Prefetch Level 0 table data to avoid cache miss if possible. + for (unsigned int i = 0; i < (*file_levels_)[0].num_files; ++i) { + auto* r = (*file_levels_)[0].files[i].fd.table_reader; + if (r) { + r->Prepare(ikey); + } + } + } + } + + FdWithKeyRange* GetNextFile() { + while (!search_ended_) { // Loops over different levels. + while (curr_index_in_curr_level_ < curr_file_level_->num_files) { + // Loops over all files in current level. + FdWithKeyRange* f = &curr_file_level_->files[curr_index_in_curr_level_]; + int cmp_largest = -1; + + // Do key range filtering of files or/and fractional cascading if: + // (1) not all the files are in level 0, or + // (2) there are more than 3 Level 0 files + // If there are only 3 or less level 0 files in the system, we skip + // the key range filtering. In this case, more likely, the system is + // highly tuned to minimize number of tables queried by each query, + // so it is unlikely that key range filtering is more efficient than + // querying the files. + if (num_levels_ > 1 || curr_file_level_->num_files > 3) { + // Check if key is within a file's range. If search left bound and + // right bound point to the same find, we are sure key falls in + // range. + assert( + curr_level_ == 0 || + curr_index_in_curr_level_ == start_index_in_curr_level_ || + user_comparator_->Compare(user_key_, + ExtractUserKey(f->smallest_key)) <= 0); + + int cmp_smallest = user_comparator_->Compare(user_key_, + ExtractUserKey(f->smallest_key)); + if (cmp_smallest >= 0) { + cmp_largest = user_comparator_->Compare(user_key_, + ExtractUserKey(f->largest_key)); + } + + // Setup file search bound for the next level based on the + // comparison results + if (curr_level_ > 0) { + file_indexer_->GetNextLevelIndex(curr_level_, + curr_index_in_curr_level_, + cmp_smallest, cmp_largest, + &search_left_bound_, + &search_right_bound_); + } + // Key falls out of current file's range + if (cmp_smallest < 0 || cmp_largest > 0) { + if (curr_level_ == 0) { + ++curr_index_in_curr_level_; + continue; + } else { + // Search next level. + break; + } + } + } +#ifndef NDEBUG + // Sanity check to make sure that the files are correctly sorted + if (prev_file_) { + if (curr_level_ != 0) { + int comp_sign = internal_comparator_->Compare( + prev_file_->largest_key, f->smallest_key); + assert(comp_sign < 0); + } else { + // level == 0, the current file cannot be newer than the previous + // one. Use compressed data structure, has no attribute seqNo + assert(curr_index_in_curr_level_ > 0); + assert(!NewestFirstBySeqNo(files_[0][curr_index_in_curr_level_], + files_[0][curr_index_in_curr_level_-1])); + } + } + prev_file_ = f; +#endif + if (curr_level_ > 0 && cmp_largest < 0) { + // No more files to search in this level. + search_ended_ = !PrepareNextLevel(); + } else { + ++curr_index_in_curr_level_; + } + return f; + } + // Start searching next level. + search_ended_ = !PrepareNextLevel(); + } + // Search ended. + return nullptr; + } + + private: + unsigned int num_levels_; + unsigned int curr_level_; + int search_left_bound_; + int search_right_bound_; + std::vector* files_; + autovector* file_levels_; + bool search_ended_; + FileLevel* curr_file_level_; + unsigned int curr_index_in_curr_level_; + unsigned int start_index_in_curr_level_; + Slice user_key_; + Slice ikey_; + FileIndexer* file_indexer_; + const Comparator* user_comparator_; + const InternalKeyComparator* internal_comparator_; +#ifndef NDEBUG + FdWithKeyRange* prev_file_; +#endif + + // Setup local variables to search next level. + // Returns false if there are no more levels to search. + bool PrepareNextLevel() { + curr_level_++; + while (curr_level_ < num_levels_) { + curr_file_level_ = &(*file_levels_)[curr_level_]; + if (curr_file_level_->num_files == 0) { + // When current level is empty, the search bound generated from upper + // level must be [0, -1] or [0, FileIndexer::kLevelMaxIndex] if it is + // also empty. + assert(search_left_bound_ == 0); + assert(search_right_bound_ == -1 || + search_right_bound_ == FileIndexer::kLevelMaxIndex); + // Since current level is empty, it will need to search all files in + // the next level + search_left_bound_ = 0; + search_right_bound_ = FileIndexer::kLevelMaxIndex; + curr_level_++; + continue; + } + + // Some files may overlap each other. We find + // all files that overlap user_key and process them in order from + // newest to oldest. In the context of merge-operator, this can occur at + // any level. Otherwise, it only occurs at Level-0 (since Put/Deletes + // are always compacted into a single entry). + int32_t start_index; + if (curr_level_ == 0) { + // On Level-0, we read through all files to check for overlap. + start_index = 0; + } else { + // On Level-n (n>=1), files are sorted. Binary search to find the + // earliest file whose largest key >= ikey. Search left bound and + // right bound are used to narrow the range. + if (search_left_bound_ == search_right_bound_) { + start_index = search_left_bound_; + } else if (search_left_bound_ < search_right_bound_) { + if (search_right_bound_ == FileIndexer::kLevelMaxIndex) { + search_right_bound_ = curr_file_level_->num_files - 1; + } + start_index = FindFileInRange(*internal_comparator_, + *curr_file_level_, ikey_, + search_left_bound_, search_right_bound_); + } else { + // search_left_bound > search_right_bound, key does not exist in + // this level. Since no comparision is done in this level, it will + // need to search all files in the next level. + search_left_bound_ = 0; + search_right_bound_ = FileIndexer::kLevelMaxIndex; + curr_level_++; + continue; + } + } + start_index_in_curr_level_ = start_index; + curr_index_in_curr_level_ = start_index; +#ifndef NDEBUG + prev_file_ = nullptr; +#endif + return true; + } + // curr_level_ = num_levels_. So, no more levels to search. + return false; + } +}; +} // anonymous namespace + static uint64_t TotalFileSize(const std::vector& files) { uint64_t sum = 0; for (size_t i = 0; i < files.size() && files[i]; i++) { @@ -82,29 +339,6 @@ Version::~Version() { delete[] files_; } -// Find File in FileLevel data structure -// Within an index range defined by left and right -int FindFileInRange(const InternalKeyComparator& icmp, - const FileLevel& file_level, - const Slice& key, - uint32_t left, - uint32_t right) { - while (left < right) { - uint32_t mid = (left + right) / 2; - const FdWithKeyRange& f = file_level.files[mid]; - if (icmp.InternalKeyComparator::Compare(f.largest_key, 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; -} - int FindFile(const InternalKeyComparator& icmp, const FileLevel& file_level, const Slice& key) { @@ -507,28 +741,6 @@ static bool SaveValue(void* arg, const ParsedInternalKey& parsed_key, return false; } -namespace { -bool NewestFirstBySeqNo(FileMetaData* a, FileMetaData* b) { - if (a->smallest_seqno != b->smallest_seqno) { - return a->smallest_seqno > b->smallest_seqno; - } - if (a->largest_seqno != b->largest_seqno) { - return a->largest_seqno > b->largest_seqno; - } - // Break ties by file number - return a->fd.GetNumber() > b->fd.GetNumber(); -} -bool BySmallestKey(FileMetaData* a, FileMetaData* b, - const InternalKeyComparator* cmp) { - int r = cmp->Compare(a->smallest, b->smallest); - if (r != 0) { - return (r < 0); - } - // Break ties by file number - return (a->fd.GetNumber() < b->fd.GetNumber()); -} -} // anonymous namespace - Version::Version(ColumnFamilyData* cfd, VersionSet* vset, uint64_t version_number) : cfd_(cfd), @@ -591,166 +803,32 @@ void Version::Get(const ReadOptions& options, saver.logger = info_log_; saver.statistics = db_statistics_; - // We can search level-by-level since entries never hop across - // levels. Therefore we are guaranteed that if we find data - // in an smaller level, later levels are irrelevant (unless we - // are MergeInProgress). - - int32_t search_left_bound = 0; - int32_t search_right_bound = FileIndexer::kLevelMaxIndex; - for (int level = 0; level < num_non_empty_levels_; ++level) { - int num_files = file_levels_[level].num_files; - if (num_files == 0) { - // When current level is empty, the search bound generated from upper - // level must be [0, -1] or [0, FileIndexer::kLevelMaxIndex] if it is - // also empty. - assert(search_left_bound == 0); - assert(search_right_bound == -1 || - search_right_bound == FileIndexer::kLevelMaxIndex); - // Since current level is empty, it will need to search all files in the - // next level - search_left_bound = 0; - search_right_bound = FileIndexer::kLevelMaxIndex; - continue; - } - - // Prefetch table data to avoid cache miss if possible - if (level == 0) { - for (int i = 0; i < num_files; ++i) { - auto* r = file_levels_[0].files[i].fd.table_reader; - if (r) { - r->Prepare(ikey); - } - } - } - - // Get the list of files to search in this level - FdWithKeyRange* files = file_levels_[level].files; - - // Some files may overlap each other. We find - // all files that overlap user_key and process them in order from - // newest to oldest. In the context of merge-operator, - // this can occur at any level. Otherwise, it only occurs - // at Level-0 (since Put/Deletes are always compacted into a single entry). - int32_t start_index; - if (level == 0) { - // On Level-0, we read through all files to check for overlap. - start_index = 0; - } else { - // On Level-n (n>=1), files are sorted. Binary search to find the earliest - // file whose largest key >= ikey. Search left bound and right bound are - // used to narrow the range. - if (search_left_bound == search_right_bound) { - start_index = search_left_bound; - } else if (search_left_bound < search_right_bound) { - if (search_right_bound == FileIndexer::kLevelMaxIndex) { - search_right_bound = num_files - 1; - } - start_index = FindFileInRange(cfd_->internal_comparator(), - file_levels_[level], ikey, - search_left_bound, search_right_bound); - } else { - // search_left_bound > search_right_bound, key does not exist in this - // level. Since no comparision is done in this level, it will need to - // search all files in the next level. - search_left_bound = 0; - search_right_bound = FileIndexer::kLevelMaxIndex; - continue; - } + FilePicker fp(files_, user_key, ikey, &file_levels_, num_non_empty_levels_, + &file_indexer_, user_comparator_, internal_comparator_); + FdWithKeyRange* f = fp.GetNextFile(); + while (f != nullptr) { + *status = table_cache_->Get(options, *internal_comparator_, f->fd, ikey, + &saver, SaveValue, MarkKeyMayExist); + // TODO: examine the behavior for corrupted key + if (!status->ok()) { + return; } - // Traverse each relevant file to find the desired key -#ifndef NDEBUG - FdWithKeyRange* prev_file = nullptr; -#endif - - for (int32_t i = start_index; i < num_files;) { - FdWithKeyRange* f = &files[i]; - assert(f->fd.GetNumber() == files_[level][i]->fd.GetNumber()); - int cmp_largest = -1; - - // Do key range filtering of files or/and fractional cascading if: - // (1) not all the files are in level 0, or - // (2) there are more than 3 Level 0 files - // If there are only 3 or less level 0 files in the system, we skip the - // key range filtering. In this case, more likely, the system is highly - // tuned to minimize number of tables queried by each query, so it is - // unlikely that key range filtering is more efficient than querying the - // files. - if (num_non_empty_levels_ > 1 || num_files > 3) { - // Check if key is within a file's range. If search left bound and right - // bound point to the same find, we are sure key falls in range. - assert( - level == 0 || i == start_index || user_comparator_->Compare( - user_key, ExtractUserKey(f->smallest_key)) <= 0); - - int cmp_smallest = user_comparator_->Compare(user_key, - ExtractUserKey(f->smallest_key)); - if (cmp_smallest >= 0) { - cmp_largest = user_comparator_->Compare(user_key, - ExtractUserKey(f->largest_key)); - } - // Setup file search bound for the next level based on the comparison - // results - if (level > 0) { - file_indexer_.GetNextLevelIndex(level, i, cmp_smallest, cmp_largest, - &search_left_bound, - &search_right_bound); - } - // Key falls out of current file's range - if (cmp_smallest < 0 || cmp_largest > 0) { - if (level == 0) { - ++i; - continue; - } else { - break; - } - } - } - -#ifndef NDEBUG - // Sanity check to make sure that the files are correctly sorted - if (prev_file) { - if (level != 0) { - int comp_sign = internal_comparator_->Compare(prev_file->largest_key, - f->smallest_key); - assert(comp_sign < 0); - } else { - // level == 0, the current file cannot be newer than the previous one. - // Use compressed data structure, has no attribute seqNo - assert(i > 0); - assert(!NewestFirstBySeqNo(files_[0][i], files_[0][i-1])); - } - } - prev_file = f; -#endif - *status = table_cache_->Get(options, *internal_comparator_, f->fd, ikey, - &saver, SaveValue, MarkKeyMayExist); - // TODO: examine the behavior for corrupted key - if (!status->ok()) { + switch (saver.state) { + case kNotFound: + break; // Keep searching in other files + case kFound: return; - } - - switch (saver.state) { - case kNotFound: - break; // Keep searching in other files - case kFound: - return; - case kDeleted: - *status = Status::NotFound(); // Use empty error message for speed - return; - case kCorrupt: - *status = Status::Corruption("corrupted key for ", user_key); - return; - case kMerge: - break; - } - if (level > 0 && cmp_largest < 0) { + case kDeleted: + *status = Status::NotFound(); // Use empty error message for speed + return; + case kCorrupt: + *status = Status::Corruption("corrupted key for ", user_key); + return; + case kMerge: break; - } else { - ++i; - } } + f = fp.GetNextFile(); } if (kMerge == saver.state) {