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VersionBuilder: optmize SaveTo() to linear time. (#4366)

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Summary:
Because `base_files` and `added_files` both are sorted, using a merge
operation to these two sorted arrays is more effective. The complexity
is reduced to linear time.

    - optmize the merge complexity.
    - move the `NDEBUG` of sorted `added_files` out of merge process.

Signed-off-by: JiYou <jiyou09@gmail.com>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4366

Differential Revision: D9833592

Pulled By: ajkr

fbshipit-source-id: dd32b67ebdca4c20e5e9546ab8082cecefe99fd0
This commit is contained in:
JiYou 2018-09-14 19:40:37 -07:00 committed by Facebook Github Bot
parent 8959063c9c
commit 82e8e9e26b
1 changed files with 15 additions and 20 deletions
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35
db/version_builder.cc
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@ -324,8 +324,6 @@ class VersionBuilder::Rep {
// Merge the set of added files with the set of pre-existing files.
// Drop any deleted files. Store the result in *v.
const auto& base_files = base_vstorage_->LevelFiles(level);
auto base_iter = base_files.begin();
auto base_end = base_files.end();
const auto& unordered_added_files = levels_[level].added_files;
vstorage->Reserve(level,
base_files.size() + unordered_added_files.size());
@ -339,30 +337,27 @@ class VersionBuilder::Rep {
std::sort(added_files.begin(), added_files.end(), cmp);
#ifndef NDEBUG
FileMetaData* prev_file = nullptr;
#endif
FileMetaData* prev_added_file = nullptr;
for (const auto& added : added_files) {
#ifndef NDEBUG
if (level > 0 && prev_file != nullptr) {
if (level > 0 && prev_added_file != nullptr) {
assert(base_vstorage_->InternalComparator()->Compare(
prev_file->smallest, added->smallest) <= 0);
prev_added_file->smallest, added->smallest) <= 0);
}
prev_file = added;
prev_added_file = added;
}
#endif
// Add all smaller files listed in base_
for (auto bpos = std::upper_bound(base_iter, base_end, added, cmp);
base_iter != bpos; ++base_iter) {
MaybeAddFile(vstorage, level, *base_iter);
auto base_iter = base_files.begin();
auto base_end = base_files.end();
auto added_iter = added_files.begin();
auto added_end = added_files.end();
while (added_iter != added_end || base_iter != base_end) {
if (base_iter == base_end ||
(added_iter != added_end && cmp(*added_iter, *base_iter))) {
MaybeAddFile(vstorage, level, *added_iter++);
} else {
MaybeAddFile(vstorage, level, *base_iter++);
}
MaybeAddFile(vstorage, level, added);
}
// Add remaining base files
for (; base_iter != base_end; ++base_iter) {
MaybeAddFile(vstorage, level, *base_iter);
}
}