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84 lines
2.2 KiB
Markdown
84 lines
2.2 KiB
Markdown
---
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sidebar_position: 9
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sidebar_label: EmbeddedRocksDB
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---
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# EmbeddedRocksDB 引擎 {#EmbeddedRocksDB-engine}
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这个引擎允许 ClickHouse 与 [rocksdb](http://rocksdb.org/) 进行集成。
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## 创建一张表 {#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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必要参数:
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- `primary_key_name` – any column name in the column list.
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- 必须指定 `primary key`, 仅支持主键中的一个列. 主键将被序列化为二进制的`rocksdb key`.
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- 主键以外的列将以相应的顺序在二进制中序列化为`rocksdb`值.
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- 带有键 `equals` 或 `in` 过滤的查询将被优化为从 `rocksdb` 进行多键查询.
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示例:
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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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## 指标
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还有一个`system.rocksdb` 表, 公开rocksdb的统计信息:
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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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## 配置
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你能修改任何[rocksdb options](https://github.com/facebook/rocksdb/wiki/Option-String-and-Option-Map) 配置，使用配置文件:
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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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[原始文章](https://clickhouse.com/docs/en/engines/table-engines/integrations/embedded-rocksdb/) <!--hide-->
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