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128 lines
3.1 KiB
Markdown
128 lines
3.1 KiB
Markdown
---
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slug: /en/engines/table-engines/integrations/redis
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sidebar_position: 175
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sidebar_label: Redis
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---
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# Redis
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This engine allows integrating ClickHouse with [Redis](https://redis.io/). For Redis takes kv model, we strongly recommend you only query it in a point way, such as `where k=xx` or `where k in (xx, xx)`.
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## Creating a Table {#creating-a-table}
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``` sql
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CREATE TABLE [IF NOT EXISTS] [db.]table_name
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(
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name1 [type1],
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name2 [type2],
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...
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) ENGINE = Redis(host:port[, db_index[, password[, pool_size]]]) PRIMARY KEY(primary_key_name);
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```
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**Engine Parameters**
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- `host:port` — Redis server address, you can ignore port and default Redis port 6379 will be used.
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- `db_index` — Redis db index range from 0 to 15, default is 0.
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- `password` — User password, default is blank string.
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- `pool_size` — Redis max connection pool size, default is 16.
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- `primary_key_name` - any column name in the column list.
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- `primary` must be specified, it supports only one column in the primary key. The primary key will be serialized in binary as a Redis key.
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- columns other than the primary key will be serialized in binary as Redis value in corresponding order.
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- queries with key equals or in filtering will be optimized to multi keys lookup from Redis. If queries without filtering key full table scan will happen which is a heavy operation.
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## Usage Example {#usage-example}
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Create a table in ClickHouse which allows to read data from Redis:
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``` sql
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CREATE TABLE redis_table
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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 = Redis('redis1:6379') PRIMARY KEY(key);
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```
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Insert:
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```sql
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INSERT INTO redis_table Values('1', 1, '1', 1.0), ('2', 2, '2', 2.0);
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```
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Query:
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``` sql
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SELECT COUNT(*) FROM redis_table;
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```
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``` text
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┌─count()─┐
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│ 2 │
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└─────────┘
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```
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``` sql
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SELECT * FROM redis_table WHERE key='1';
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```
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```text
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┌─key─┬─v1─┬─v2─┬─v3─┐
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│ 1 │ 1 │ 1 │ 1 │
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└─────┴────┴────┴────┘
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```
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``` sql
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SELECT * FROM redis_table WHERE v1=2;
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```
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```text
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┌─key─┬─v1─┬─v2─┬─v3─┐
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│ 2 │ 2 │ 2 │ 2 │
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└─────┴────┴────┴────┘
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```
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Update:
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Note that the primary key cannot be updated.
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```sql
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ALTER TABLE redis_table UPDATE v1=2 WHERE key='1';
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```
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Delete:
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```sql
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ALTER TABLE redis_table DELETE WHERE key='1';
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```
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Truncate:
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Flush Redis db asynchronously. Also `Truncate` support SYNC mode.
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```sql
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TRUNCATE TABLE redis_table SYNC;
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```
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Join:
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Join with other tables.
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```
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SELECT * FROM redis_table JOIN merge_tree_table ON merge_tree_table.key=redis_table.key;
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```
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## Limitations {#limitations}
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Redis engine also supports scanning queries, such as `where k > xx`, but it has some limitations:
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1. Scanning query may produce some duplicated keys in a very rare case when it is rehashing. See details in [Redis Scan](https://github.com/redis/redis/blob/e4d183afd33e0b2e6e8d1c79a832f678a04a7886/src/dict.c#L1186-L1269).
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2. During the scanning, keys could be created and deleted, so the resulting dataset can not represent a valid point in time.
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