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