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