ClickHouse/docs/en/engines/table-engines/integrations/embedded-rocksdb.md
2021-12-01 20:12:10 +00:00

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---
toc_priority: 9
toc_title: EmbeddedRocksDB
---
# EmbeddedRocksDB Engine {#EmbeddedRocksDB-engine}
This engine allows integrating ClickHouse with [rocksdb](http://rocksdb.org/).
## Creating a Table {#table_engine-EmbeddedRocksDB-creating-a-table}
``` sql
CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
(
name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1],
name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2],
...
) ENGINE = EmbeddedRocksDB PRIMARY KEY(primary_key_name)
```
Required parameters:
- `primary_key_name` any column name in the column list.
- `primary key` must be specified, it supports only one column in the primary key. The primary key will be serialized in binary as a `rocksdb key`.
- columns other than the primary key will be serialized in binary as `rocksdb` value in corresponding order.
- queries with key `equals` or `in` filtering will be optimized to multi keys lookup from `rocksdb`.
Example:
``` sql
CREATE TABLE test
(
`key` String,
`v1` UInt32,
`v2` String,
`v3` Float32
)
ENGINE = EmbeddedRocksDB
PRIMARY KEY key
```
## Metrics
There is also `system.rocksdb` table, that expose rocksdb statistics:
```sql
SELECT
name,
value
FROM system.rocksdb
┌─name──────────────────────┬─value─┐
no.file.opens 1
number.block.decompressed 1
└───────────────────────────┴───────┘
```
## Configuration
You can also change any [rocksdb options](https://github.com/facebook/rocksdb/wiki/Option-String-and-Option-Map) using config:
```xml
<rocksdb>
<options>
<max_background_jobs>8</max_background_jobs>
</options>
<column_family_options>
<num_levels>2</num_levels>
</column_family_options>
<tables>
<table>
<name>TABLE</name>
<options>
<max_background_jobs>8</max_background_jobs>
</options>
<column_family_options>
<num_levels>2</num_levels>
</column_family_options>
</table>
</tables>
</rocksdb>
```
[Original article](https://clickhouse.com/docs/en/engines/table-engines/integrations/embedded-rocksdb/) <!--hide-->