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Merge pull request #3348 from pkutaj/fix_table_formatting_in_compression_doc
docs: fix table formatting
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‎docs/data-compression/compression-in-clickhouse.md

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@@ -36,30 +36,30 @@ FROM system.columns
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WHERE table = 'posts'
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GROUP BY name
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┌─name──────────────────┬─compressed_size─┬─uncompressed_size─┬───ratio─┐
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│ Body │ 46.14 GiB │ 127.31 GiB │ 2.76 │
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│ Title │ 1.20 GiB │ 2.63 GiB │ 2.19 │
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│ Score │ 84.77 MiB │ 736.45 MiB │ 8.69 │
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│ Tags │ 475.56 MiB │ 1.40 GiB │ 3.02 │
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│ ParentId │ 210.91 MiB │ 696.20 MiB │ 3.3 │
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│ Id │ 111.17 MiB │ 736.45 MiB │ 6.62 │
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│ AcceptedAnswerId │ 81.55 MiB │ 736.45 MiB │ 9.03 │
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│ ClosedDate │ 13.99 MiB │ 517.82 MiB │ 37.02 │
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│ LastActivityDate │ 489.84 MiB │ 964.64 MiB │ 1.97 │
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│ CommentCount │ 37.62 MiB │ 565.30 MiB │ 15.03 │
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│ OwnerUserId │ 368.98 MiB │ 736.45 MiB │ 2 │
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│ AnswerCount │ 21.82 MiB │ 622.35 MiB │ 28.53 │
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│ FavoriteCount │ 280.95 KiB │ 508.40 MiB │ 1853.02 │
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│ ViewCount │ 95.77 MiB │ 736.45 MiB │ 7.69 │
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│ LastEditorUserId │ 179.47 MiB │ 736.45 MiB │ 4.1 │
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│ ContentLicense │ 5.45 MiB │ 847.92 MiB │ 155.5 │
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│ OwnerDisplayName │ 14.30 MiB │ 142.58 MiB │ 9.97 │
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│ PostTypeId │ 20.93 MiB │ 565.30 MiB │ 27 │
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│ CreationDate │ 314.17 MiB │ 964.64 MiB │ 3.07 │
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│ LastEditDate │ 346.32 MiB │ 964.64 MiB │ 2.79 │
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│ LastEditorDisplayName │ 5.46 MiB │ 124.25 MiB │ 22.75 │
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│ CommunityOwnedDate │ 2.21 MiB │ 509.60 MiB │ 230.94 │
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└───────────────────────┴─────────────────┴───────────────────┴─────────┘
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┌─name──────────────────┬─compressed_size─┬─uncompressed_size─┬───ratio────┐
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│ Body │ 46.14 GiB │ 127.31 GiB │ 2.76 │
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│ Title │ 1.20 GiB │ 2.63 GiB │ 2.19 │
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│ Score │ 84.77 MiB │ 736.45 MiB │ 8.69 │
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│ Tags │ 475.56 MiB │ 1.40 GiB │ 3.02 │
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│ ParentId │ 210.91 MiB │ 696.20 MiB │ 3.3 │
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│ Id │ 111.17 MiB │ 736.45 MiB │ 6.62 │
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│ AcceptedAnswerId │ 81.55 MiB │ 736.45 MiB │ 9.03 │
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│ ClosedDate │ 13.99 MiB │ 517.82 MiB │ 37.02 │
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│ LastActivityDate │ 489.84 MiB │ 964.64 MiB │ 1.97 │
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│ CommentCount │ 37.62 MiB │ 565.30 MiB │ 15.03 │
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│ OwnerUserId │ 368.98 MiB │ 736.45 MiB │ 2 │
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│ AnswerCount │ 21.82 MiB │ 622.35 MiB │ 28.53 │
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│ FavoriteCount │ 280.95 KiB │ 508.40 MiB │ 1853.02 │
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│ ViewCount │ 95.77 MiB │ 736.45 MiB │ 7.69 │
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│ LastEditorUserId │ 179.47 MiB │ 736.45 MiB │ 4.1 │
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│ ContentLicense │ 5.45 MiB │ 847.92 MiB │ 155.5 │
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│ OwnerDisplayName │ 14.30 MiB │ 142.58 MiB │ 9.97 │
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│ PostTypeId │ 20.93 MiB │ 565.30 MiB │ 27 │
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│ CreationDate │ 314.17 MiB │ 964.64 MiB │ 3.07 │
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│ LastEditDate │ 346.32 MiB │ 964.64 MiB │ 2.79 │
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│ LastEditorDisplayName │ 5.46 MiB │ 124.25 MiB │ 22.75 │
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│ CommunityOwnedDate │ 2.21 MiB │ 509.60 MiB │ 230.94 │
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└───────────────────────┴─────────────────┴───────────────────┴────────────┘
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```
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We show both a compressed and uncompressed size here. Both are important. The compressed size equates to what we will need to read off disk - something we want to minimize for query performance (and storage cost). This data will need to be decompressed prior to reading. The size of this uncompressed size will be dependent on the data type used in this case. Minimizing this size will reduce memory overhead of queries and the amount of data which has to be processed by the query, improving utilization of caches and ultimately query times.
@@ -76,7 +76,7 @@ FROM system.columns
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WHERE table = 'posts'
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┌─compressed_size─┬─uncompressed_size─┬─ratio─┐
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│ 50.16 GiB │ 143.47 GiB │ 2.86 │
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│ 50.16 GiB │ 143.47 GiB │ 2.86 │
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└─────────────────┴───────────────────┴───────┘
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```
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@@ -91,7 +91,7 @@ FROM system.columns
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WHERE `table` = 'posts_v3'
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┌─compressed_size─┬─uncompressed_size─┬─ratio─┐
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│ 25.15 GiB │ 68.87 GiB │ 2.74 │
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│ 25.15 GiB │ 68.87 GiB │ 2.74 │
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└─────────────────┴───────────────────┴───────┘
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```
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@@ -206,17 +206,17 @@ ORDER BY
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`table` ASC
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┌─table────┬─name────────┬─compressed_size─┬─uncompressed_size─┬─ratio─┐
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│ posts_v3 │ AnswerCount │ 9.67 MiB │ 113.69 MiB │ 11.76 │
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│ posts_v4 │ AnswerCount │ 10.39 MiB │ 111.31 MiB │ 10.71 │
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│ posts_v3 │ Id │ 159.70 MiB │ 227.38 MiB │ 1.42 │
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│ posts_v4 │ Id │ 64.91 MiB │ 222.63 MiB │ 3.43 │
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│ posts_v3 │ ViewCount │ 45.04 MiB │ 227.38 MiB │ 5.05 │
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│ posts_v4 │ ViewCount │ 52.72 MiB │ 222.63 MiB │ 4.22 │
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│ posts_v3 │ AnswerCount │ 9.67 MiB │ 113.69 MiB │ 11.76 │
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│ posts_v4 │ AnswerCount │ 10.39 MiB │ 111.31 MiB │ 10.71 │
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│ posts_v3 │ Id │ 159.70 MiB │ 227.38 MiB │ 1.42 │
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│ posts_v4 │ Id │ 64.91 MiB │ 222.63 MiB │ 3.43 │
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│ posts_v3 │ ViewCount │ 45.04 MiB │ 227.38 MiB │ 5.05 │
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│ posts_v4 │ ViewCount │ 52.72 MiB │ 222.63 MiB │ 4.22 │
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└──────────┴─────────────┴─────────────────┴───────────────────┴───────┘
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6 rows in set. Elapsed: 0.008 sec
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```
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### Compression in ClickHouse Cloud {#compression-in-clickhouse-cloud}
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In ClickHouse Cloud, we utilize the `ZSTD` compression algorithm (with a default value of 1) by default. While compression speeds can vary for this algorithm, depending on the compression level (higher = slower), it has the advantage of being consistently fast on decompression (around 20% variance) and also benefiting from the ability to be parallelized. Our historical tests also suggest that this algorithm is often sufficiently effective and can even outperform `LZ4` combined with a codec. It is effective on most data types and information distributions, and is thus a sensible general-purpose default and why our initial earlier compression is already excellent even without optimization.
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In ClickHouse Cloud, we utilize the `ZSTD` compression algorithm (with a default value of 1) by default. While compression speeds can vary for this algorithm, depending on the compression level (higher = slower), it has the advantage of being consistently fast on decompression (around 20% variance) and also benefiting from the ability to be parallelized. Our historical tests also suggest that this algorithm is often sufficiently effective and can even outperform `LZ4` combined with a codec. It is effective on most data types and information distributions, and is thus a sensible general-purpose default and why our initial earlier compression is already excellent even without optimization.

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