MyRocks Column Families
MyRocks stores data in column families. These are similar to tablespaces.
By default, the data is stored in the default column family.
One can specify which column family the data goes to by using index comments:
INDEX index_name(col1, col2, ...) COMMENT 'column_family_name'
Contents
If the column name starts with rev:, the column family is reverse-ordered.
Reasons for Column Families
Storage parameters like
- Bloom filter settings
- Compression settings
- Whether the data is stored in reverse order
are specified on a per-column family basis.
Creating a Column Family
When creating a table or index, you can specify the name of the column family for it. If the column family doesn't exist, it will be automatically created.
Dropping a Column Family
There is currently no way to drop a column family. RocksDB supports this internally but MyRocks doesn't provide any way to do it.
Setting Column Family Parameters
Use these variables:
- rocksdb_default_cf_options - a my.cnf parameter specifying default options for all column families.
- rocksdb_override_cf_options - a my.cnf parameter specifying per-column family option overrides.
- rocksdb_update_cf_options - a dynamically-settable variable which allows to change parameters online. Not all parameters can be changed.
rocksdb_override_cf_options
This parameter allows one to override column family options for specific column families. Here is an example of how to set option1=value1 and option2=value for column family cf1, and option3=value3 for column family cf3:
rocksdb_override_cf_options='cf1={option1=value1;option2=value2};cf2={option3=value3}'
One can check the contents of INFORMATION_SCHEMA.ROCKSDB_CF_OPTIONS to see what options are available.
Options that are frequently configured are:
- Data compression. See myrocks-and-data-compression.
- Bloom Filters. See myrocks-and-bloom-filters.
Examining Column Family Parameters
See the INFORMATION_SCHEMA.ROCKSDB_CF_OPTIONS table.
