# MyRocks Column Families

[MyRocks](https://mariadb.com/docs/server/server-usage/storage-engines/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:

```sql
INDEX index_name(col1, col2, ...) COMMENT 'column_family_name'
```

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 are 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](https://mariadb.com/docs/server/server-usage/storage-engines/myrocks-system-variables#rocksdb_default_cf_options) - a my.cnf parameter specifying default options for all column families.
* [rocksdb\_override\_cf\_options](https://mariadb.com/docs/server/server-usage/storage-engines/myrocks-system-variables#rocksdb_override_cf_options) - a my.cnf parameter specifying per-column family option overrides.
* [rocksdb\_update\_cf\_options](https://mariadb.com/docs/server/server-usage/storage-engines/myrocks-system-variables#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](https://mariadb.com/docs/server/server-usage/storage-engines/myrocks/myrocks-and-data-compression).
* Bloom Filters. See [myrocks-and-bloom-filters](https://mariadb.com/docs/server/server-usage/storage-engines/myrocks/myrocks-and-bloom-filters).

## Examining Column Family Parameters

See the [INFORMATION\_SCHEMA.ROCKSDB\_CF\_OPTIONS](https://mariadb.com/docs/server/reference/system-tables/information-schema/information-schema-tables/information-schema-myrocks-tables/information-schema-rocksdb_cf_options-table) table.

<sub>*This page is licensed: CC BY-SA / Gnu FDL*</sub>

{% @marketo/form formId="4316" %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mariadb.com/docs/server/server-usage/storage-engines/myrocks/myrocks-column-families.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.