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123 lines
3.4 KiB
Markdown
123 lines
3.4 KiB
Markdown
---
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slug: /en/engines/table-engines/integrations/embedded-rocksdb
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sidebar_position: 9
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sidebar_label: EmbeddedRocksDB
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---
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# 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([ttl, rocksdb_dir, read_only]) PRIMARY KEY(primary_key_name)
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```
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Engine parameters:
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- `ttl` - time to live for values. TTL is accepted in seconds. If TTL is 0, regular RocksDB instance is used (without TTL).
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- `rocksdb_dir` - path to the directory of an existed RocksDB or the destination path of the created RocksDB. Open the table with the specified `rocksdb_dir`.
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- `read_only` - when `read_only` is set to true, read-only mode is used. For storage with TTL, compaction will not be triggered (neither manual nor automatic), so no expired entries are removed.
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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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## Supported operations {#table_engine-EmbeddedRocksDB-supported-operations}
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### Inserts
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When new rows are inserted into `EmbeddedRocksDB`, if the key already exists, the value will be updated, otherwise a new key is created.
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Example:
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```sql
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INSERT INTO test VALUES ('some key', 1, 'value', 3.2);
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```
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### Deletes
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Rows can be deleted using `DELETE` query or `TRUNCATE`.
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```sql
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DELETE FROM test WHERE key LIKE 'some%' AND v1 > 1;
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```
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```sql
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ALTER TABLE test DELETE WHERE key LIKE 'some%' AND v1 > 1;
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```
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```sql
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TRUNCATE TABLE test;
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```
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### Updates
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Values can be updated using the `ALTER TABLE` query. The primary key cannot be updated.
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```sql
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ALTER TABLE test UPDATE v1 = v1 * 10 + 2 WHERE key LIKE 'some%' AND v3 > 3.1;
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```
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