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Refactoring Version::Get()

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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
This commit is contained in:
Radheshyam Balasundaram 2014-07-16 13:33:02 -07:00
parent c11d604ab3
commit 0418e66e2a
1 changed files with 278 additions and 200 deletions
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446
db/version_set.cc
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@ -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<FileMetaData*>* files,
const Slice& user_key,
const Slice& ikey,
autovector<FileLevel>* 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<FileMetaData*>* files_;
autovector<FileLevel>* 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<FileMetaData*>& 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),
@ -591,139 +803,10 @@ 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;
}
}
// 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
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
@ -745,12 +828,7 @@ void Version::Get(const ReadOptions& options,
case kMerge:
break;
}
if (level > 0 && cmp_largest < 0) {
break;
} else {
++i;
}
}
f = fp.GetNextFile();
}
if (kMerge == saver.state) {