Sparse serialization and ColumnSparse#22535
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alesapin merged 102 commits intoClickHouse:masterfrom Dec 17, 2021
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| /// Convert to full column, because sparse column has | ||
| /// access to element in O(log(K)), where K is number of non-default rows, | ||
| /// which can be inefficient. | ||
| convertToFullIfSparse(chunk); |
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I think it's better to add such comments for each place where we use convertToFullIfSparse. Because it looks like code here works with some column internals, but just not ready for sparse format.
alesapin
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Dec 8, 2021
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Tests Ok, let's merge! |
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Internal documentation ticket: DOCSUP-20369 |
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Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Implemented sparse serialization. It can reduce usage of disk space and improve performance of some queries for columns, which contain a lot of default (zero) values. It can be enabled by setting
ratio_of_defaults_for_sparse_serialization. Sparse serialization will be chosen dynamically for column, if it has ratio of number of default values to number of all values above that threshold. Serialization (default or sparse) will be fixed for every column in part, but may varies between parts.Detailed description / Documentation draft:
Second part of #19953.
TODO:
ColumnSparse.