3.4 KiB
| title | description |
|---|---|
| Configurable Column Compression | Configurable column storage compression method |
Since TDengine 3.3.0.0, more advanced compression feature is introduced, you can specify compression or not, the compression method and compression level for each column.
Compression Terminology Definition
Compression Level Definition
- Level 1 Compression: Encoding the data, which is essentially a form of compression
- Level 2 Compression: Compressing data blocks.
Compression Algorithm Level
In this article, it specifically refers to the level within the secondary compression algorithm, such as zstd, at least 8 levels can be selected, each level has different performance, essentially it is a tradeoff between compression ratio, compression speed, and decompression speed. To avoid the difficulty of choice, it is simplified and defined as the following three levels:
- high: The highest compression ratio, the worst compression speed and decompression speed.
- low: The best compression speed and decompression speed, the lowest compression ratio.
- medium: Balancing compression ratio, compression speed, and decompression speed.
Compression Algorithm List
-
Encoding algorithm list (Level 1 compression): simple8b, bit-packing, delta-i, delta-d, disabled
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Compression algorithm list (Level 2 compression): lz4, zlib, zstd, tsz, xz, disabled
-
Default compression algorithm list and applicable range for each data type
| Data Type | Optional Encoding Algorithm | Default Encoding Algorithm | Optional Compression Algorithm | Default Compression Algorithm | Default Compression Level |
|---|---|---|---|---|---|
| tinyint/untinyint/smallint/usmallint/int/uint | simple8b | simple8b | lz4/zlib/zstd/xz | lz4 | medium |
| bigint/ubigint/timestamp | simple8b/delta-i | delta-i | lz4/zlib/zstd/xz | lz4 | medium |
| float/double | delta-d | delta-d | lz4/zlib/zstd/xz/tsz | lz4 | medium |
| binary/nchar | disabled | disabled | lz4/zlib/zstd/xz | lz4 | medium |
| bool | bit-packing | bit-packing | lz4/zlib/zstd/xz | lz4 | medium |
SQL
Create Table with Compression
CREATE [dbname.]tabname (colName colType [ENCODE 'encode_type'] [COMPRESS 'compress_type' [LEVEL 'level'], [, other cerate_definition]...])
Parameter Description
- tabname: Super table or ordinary table name
- encode_type: Level 1 compression, specific parameters see the above list
- compress_type: Level 2 compression, specific parameters see the above list
- level: Specifically refers to the level of secondary compression, the default value is medium, supports abbreviation as 'h'/'l'/'m'
Function Description
- Specify the compression method for the column when creating a table
Change Compression Method
ALTER TABLE [db_name.]tabName MODIFY COLUMN colName [ENCODE 'ecode_type'] [COMPRESS 'compress_type'] [LEVEL "high"]
Parameter Description
- tabName: Table name, can be a super table or an ordinary table
- colName: The column to change the compression algorithm, can only be a normal column
Function Description
- Change the compression method of the column
View Compression Method
DESCRIBE [dbname.]tabName
Function Description
- Display basic information of the column, including type and compression method
Compatibility
- Fully compatible with existing data
- Can't be rolled back once you upgrade to 3.3.0.0