MySQL :: MySQL 5.7 Reference Manual :: 14.9.1.2 Creating Compressed Tables (original) (raw)

14.9.1.2 Creating Compressed Tables

Compressed tables can be created infile-per-table tablespaces or ingeneral tablespaces. Table compression is not available for the InnoDB system tablespace. The system tablespace (space 0, the.ibdata files) can contain user-created tables, but it also contains internal system data, which is never compressed. Thus, compression applies only to tables (and indexes) stored in file-per-table or general tablespaces.

Creating a Compressed Table in File-Per-Table Tablespace

To create a compressed table in a file-per-table tablespace,innodb_file_per_table must be enabled (the default in MySQL 5.6.6) andinnodb_file_format must be set to Barracuda. You can set these parameters in the MySQL configuration file (my.cnf ormy.ini) or dynamically, using aSET statement.

After the innodb_file_per_table and innodb_file_format options are configured, specify theROW_FORMAT=COMPRESSED clause orKEY_BLOCK_SIZE clause, or both, in aCREATE TABLE orALTER TABLE statement to create a compressed table in a file-per-table tablespace.

For example, you might use the following statements:

SET GLOBAL innodb_file_per_table=1;
SET GLOBAL innodb_file_format=Barracuda;
CREATE TABLE t1
 (c1 INT PRIMARY KEY)
 ROW_FORMAT=COMPRESSED
 KEY_BLOCK_SIZE=8;

Creating a Compressed Table in a General Tablespace

To create a compressed table in a general tablespace,FILE_BLOCK_SIZE must be defined for the general tablespace, which is specified when the tablespace is created. The FILE_BLOCK_SIZE value must be a valid compressed page size in relation to theinnodb_page_size value, and the page size of the compressed table, defined by theCREATE TABLE orALTER TABLE KEY_BLOCK_SIZE clause, must be equal toFILE_BLOCK_SIZE/1024. For example, ifinnodb_page_size=16384 andFILE_BLOCK_SIZE=8192, theKEY_BLOCK_SIZE of the table must be 8. For more information, see Section 14.6.3.3, “General Tablespaces”.

The following example demonstrates creating a general tablespace and adding a compressed table. The example assumes a defaultinnodb_page_size of 16K. TheFILE_BLOCK_SIZE of 8192 requires that the compressed table have a KEY_BLOCK_SIZE of 8.

mysql> CREATE TABLESPACE `ts2` ADD DATAFILE 'ts2.ibd' FILE_BLOCK_SIZE = 8192 Engine=InnoDB;

mysql> CREATE TABLE t4 (c1 INT PRIMARY KEY) TABLESPACE ts2 ROW_FORMAT=COMPRESSED KEY_BLOCK_SIZE=8;

Notes

• If you specify ROW_FORMAT=COMPRESSED, you can omit KEY_BLOCK_SIZE; theKEY_BLOCK_SIZE setting defaults to half the innodb_page_size value.
• If you specify a valid KEY_BLOCK_SIZE value, you can omitROW_FORMAT=COMPRESSED; compression is enabled automatically.
• To determine the best value forKEY_BLOCK_SIZE, typically you create several copies of the same table with different values for this clause, then measure the size of the resulting.ibd files and see how well each performs with a realisticworkload. For general tablespaces, keep in mind that dropping a table does not reduce the size of the general tablespace.ibd file, nor does it return disk space to the operating system. For more information, seeSection 14.6.3.3, “General Tablespaces”.
• The KEY_BLOCK_SIZE value is treated as a hint; a different size could be used byInnoDB if necessary. For file-per-table tablespaces, the KEY_BLOCK_SIZE can only be less than or equal to theinnodb_page_size value. If you specify a value greater than theinnodb_page_size value, the specified value is ignored, a warning is issued, andKEY_BLOCK_SIZE is set to half of theinnodb_page_size value. Ifinnodb_strict_mode=ON, specifying an invalid KEY_BLOCK_SIZE value returns an error. For general tablespaces, validKEY_BLOCK_SIZE values depend on theFILE_BLOCK_SIZE setting of the tablespace. For more information, seeSection 14.6.3.3, “General Tablespaces”.
• 32KB and 64KB page sizes do not support compression. For more information, refer to theinnodb_page_size documentation.
• The default uncompressed size of InnoDB data pages is 16KB. Depending on the combination of option values, MySQL uses a page size of 1KB, 2KB, 4KB, 8KB, or 16KB for the tablespace data file (.ibd file). The actual compression algorithm is not affected by theKEY_BLOCK_SIZE value; the value determines how large each compressed chunk is, which in turn affects how many rows can be packed into each compressed page.
• When creating a compressed table in a file-per-table tablespace, setting KEY_BLOCK_SIZE equal to the InnoDB page size does not typically result in much compression. For example, settingKEY_BLOCK_SIZE=16 typically would not result in much compression, since the normalInnoDB page size is 16KB. This setting may still be useful for tables with many longBLOB,VARCHAR orTEXT columns, because such values often do compress well, and might therefore require fewer overflow pages as described inSection 14.9.1.5, “How Compression Works for InnoDB Tables”. For general tablespaces, a KEY_BLOCK_SIZE value equal to the InnoDB page size is not permitted. For more information, seeSection 14.6.3.3, “General Tablespaces”.
• All indexes of a table (including theclustered index) are compressed using the same page size, as specified in theCREATE TABLE or ALTER TABLE statement. Table attributes such asROW_FORMAT andKEY_BLOCK_SIZE are not part of theCREATE INDEX syntax forInnoDB tables, and are ignored if they are specified (although, if specified, they appear in the output of the SHOW CREATE TABLE statement).
• For performance-related configuration options, seeSection 14.9.1.3, “Tuning Compression for InnoDB Tables”.

Restrictions on Compressed Tables

• MySQL versions prior to 5.1 cannot process compressed tables.
• Compressed tables cannot be stored in theInnoDB system tablespace.
• General tablespaces can contain multiple tables, but compressed and uncompressed tables cannot coexist within the same general tablespace.
• Compression applies to an entire table and all its associated indexes, not to individual rows, despite the clause name ROW_FORMAT.