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[RocksDB Performance Branch] Avoid sorting in Version::Get() by presorting them in VersionSet::Builder::SaveTo()

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Summary: Pre-sort files in VersionSet::Builder::SaveTo() so that when getting the value, no need to sort them. It can avoid the costs of vector operations and sorting in Version::Get().

Test Plan: make all check

Reviewers: haobo, kailiu, dhruba

Reviewed By: dhruba

CC: nkg-, igor, leveldb

Differential Revision: https://reviews.facebook.net/D14409
This commit is contained in:
Siying Dong 2013-12-09 14:28:26 -08:00
parent 0304e3d2ff
commit bc5dd19b14
1 changed files with 42 additions and 42 deletions
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66
db/version_set.cc
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@ -450,17 +450,12 @@ void Version::Get(const ReadOptions& options,
// levels. Therefore we are guaranteed that if we find data
// in an smaller level, later levels are irrelevant (unless we
// are MergeInProgress).
std::vector<FileMetaData*> important_files;
for (int level = 0; level < vset_->NumberLevels(); level++) {
size_t num_files = files_[level].size();
if (num_files == 0) continue;
// Get the list of files to search in this level
FileMetaData* const* files = &files_[level][0];
important_files.clear();
if (level == 0) {
important_files.reserve(num_files);
}
// Some files may overlap each other. We find
// all files that overlap user_key and process them in order from
@ -478,44 +473,42 @@ void Version::Get(const ReadOptions& options,
start_index = FindFile(vset_->icmp_, files_[level], ikey);
}
// Traverse the list, finding all overlapping files.
for (uint32_t i = start_index; i < num_files; i++) {
// Traverse each relevant file to find the desired key
#ifndef NDEBUG
FileMetaData* prev_file = nullptr;
#endif
for (uint32_t i = start_index; i < num_files; ++i) {
FileMetaData* f = files[i];
if (ucmp->Compare(user_key, f->smallest.user_key()) >= 0 &&
ucmp->Compare(user_key, f->largest.user_key()) <= 0) {
important_files.push_back(f);
} else if (level > 0) {
if (ucmp->Compare(user_key, f->smallest.user_key()) < 0 ||
ucmp->Compare(user_key, f->largest.user_key()) > 0) {
// Only process overlapping files.
if (level > 0) {
// If on Level-n (n>=1) then the files are sorted.
// So we can stop looking when we are past the ikey.
break;
}
// TODO: do we want to check file ranges for level0 files at all?
// For new SST format where Get() is fast, we might want to consider
// to avoid those two comparisons, if it can filter out too few files.
continue;
}
if (important_files.empty()) continue;
if (level == 0) {
if (vset_->options_->compaction_style == kCompactionStyleUniversal) {
std::sort(important_files.begin(), important_files.end(), NewestFirstBySeqNo);
} else {
std::sort(important_files.begin(), important_files.end(), NewestFirst);
}
} else {
// Sanity check to make sure that the files are correctly sorted
#ifndef NDEBUG
num_files = important_files.size();
for (uint32_t i = 1; i < num_files; ++i) {
FileMetaData* a = important_files[i-1];
FileMetaData* b = important_files[i];
int comp_sign = vset_->icmp_.Compare(a->largest, b->smallest);
// Sanity check to make sure that the files are correctly sorted
if (prev_file) {
if (level != 0) {
int comp_sign = vset_->icmp_.Compare(prev_file->largest, f->smallest);
assert(comp_sign < 0);
} else {
// level == 0, the current file cannot be newer than the previous one.
if (vset_->options_->compaction_style == kCompactionStyleUniversal) {
assert(!NewestFirstBySeqNo(f, prev_file));
} else {
assert(!NewestFirst(f, prev_file));
}
}
}
prev_file = f;
#endif
}
// Traverse each relevant file to find the desired key
num_files = important_files.size();
for (uint32_t i = 0; i < num_files; ++i) {
FileMetaData* f = important_files[i];
bool tableIO = false;
*status = vset_->table_cache_->Get(options, f->number, f->file_size,
ikey, &saver, SaveValue, &tableIO,
@ -1113,6 +1106,13 @@ class VersionSet::Builder {
MaybeAddFile(v, level, *base_iter);
}
}
// Pre-sort level0 for Get()
if (vset_->options_->compaction_style == kCompactionStyleUniversal) {
std::sort(v->files_[0].begin(), v->files_[0].end(), NewestFirstBySeqNo);
} else {
std::sort(v->files_[0].begin(), v->files_[0].end(), NewestFirst);
}
CheckConsistency(v);
}