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Improve code comments in EstimateLiveDataSize (#7072) 

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/7072

Reviewed By: ajkr

Differential Revision: D22391641

Pulled By: pdillinger

fbshipit-source-id: 0ef355576454514263ab684eb1a5c06787f3242a
This commit is contained in:
Peter Dillinger 2020-07-06 16:15:16 -07:00 committed by Facebook GitHub Bot
parent 899e59ecb7
commit 4b107ceb7e
1 changed files with 7 additions and 6 deletions
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13
db/version_set.cc
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@ -3407,22 +3407,23 @@ void VersionStorageInfo::CalculateBaseBytes(const ImmutableCFOptions& ioptions,
}
uint64_t VersionStorageInfo::EstimateLiveDataSize() const {
// Estimate the live data size by adding up the size of the last level for all
// key ranges. Note: Estimate depends on the ordering of files in level 0
// because files in level 0 can be overlapping.
// Estimate the live data size by adding up the size of a maximal set of
// sst files with no range overlap in same or higher level. The less
// compacted, the more optimistic (smaller) this estimate is. Also,
// for multiple sorted runs within a level, file order will matter.
uint64_t size = 0;
auto ikey_lt = [this](InternalKey* x, InternalKey* y) {
return internal_comparator_->Compare(*x, *y) < 0;
};
// (Ordered) map of largest keys in non-overlapping files
// (Ordered) map of largest keys in files being included in size estimate
std::map<InternalKey*, FileMetaData*, decltype(ikey_lt)> ranges(ikey_lt);
for (int l = num_levels_ - 1; l >= 0; l--) {
bool found_end = false;
for (auto file : files_[l]) {
// Find the first file where the largest key is larger than the smallest
// key of the current file. If this file does not overlap with the
// Find the first file already included with largest key is larger than
// the smallest key of `file`. If that file does not overlap with the
// current file, none of the files in the map does. If there is
// no potential overlap, we can safely insert the rest of this level
// (if the level is not 0) into the map without checking again because