mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-16 12:44:42 +00:00
120 lines
3.0 KiB
Markdown
120 lines
3.0 KiB
Markdown
---
|
|
slug: /en/engines/table-engines/integrations/redis
|
|
sidebar_position: 43
|
|
sidebar_label: Redis
|
|
---
|
|
|
|
# Redis
|
|
|
|
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)`.
|
|
|
|
## Creating a Table {#creating-a-table}
|
|
|
|
``` sql
|
|
CREATE TABLE [IF NOT EXISTS] [db.]table_name
|
|
(
|
|
name1 [type1],
|
|
name2 [type2],
|
|
...
|
|
) ENGINE = Redis(host:port[, db_index[, password[, pool_size]]]) PRIMARY KEY(primary_key_name);
|
|
```
|
|
|
|
**Engine Parameters**
|
|
|
|
- `host:port` — Redis server address, you can ignore port and default Redis port 6379 will be used.
|
|
|
|
- `db_index` — Redis db index range from 0 to 15, default is 0.
|
|
|
|
- `password` — User password, default is blank string.
|
|
|
|
- `pool_size` — Redis max connection pool size, default is 16.
|
|
|
|
- `primary_key_name` - any column name in the column list.
|
|
|
|
- `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.
|
|
|
|
- columns other than the primary key will be serialized in binary as Redis value in corresponding order.
|
|
|
|
- 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.
|
|
|
|
## Usage Example {#usage-example}
|
|
|
|
Create a table in ClickHouse which allows to read data from Redis:
|
|
|
|
``` sql
|
|
CREATE TABLE redis_table
|
|
(
|
|
`k` String,
|
|
`m` String,
|
|
`n` UInt32
|
|
)
|
|
ENGINE = Redis('redis1:6379') PRIMARY KEY(k);
|
|
```
|
|
|
|
Insert:
|
|
|
|
```sql
|
|
INSERT INTO redis_table Values('1', 1, '1', 1.0), ('2', 2, '2', 2.0);
|
|
```
|
|
|
|
Query:
|
|
|
|
``` sql
|
|
SELECT COUNT(*) FROM redis_table;
|
|
```
|
|
|
|
``` text
|
|
┌─count()─┐
|
|
│ 2 │
|
|
└─────────┘
|
|
```
|
|
|
|
``` sql
|
|
SELECT * FROM redis_table WHERE key='1';
|
|
```
|
|
|
|
```text
|
|
┌─key─┬─v1─┬─v2─┬─v3─┐
|
|
│ 1 │ 1 │ 1 │ 1 │
|
|
└─────┴────┴────┴────┘
|
|
```
|
|
|
|
``` sql
|
|
SELECT * FROM redis_table WHERE v1=2;
|
|
```
|
|
|
|
```text
|
|
┌─key─┬─v1─┬─v2─┬─v3─┐
|
|
│ 2 │ 2 │ 2 │ 2 │
|
|
└─────┴────┴────┴────┘
|
|
```
|
|
|
|
Update:
|
|
|
|
Note that the primary key cannot be updated.
|
|
|
|
```sql
|
|
ALTER TABLE redis_table UPDATE v1=2 WHERE key='1';
|
|
```
|
|
|
|
Delete:
|
|
|
|
```sql
|
|
ALTER TABLE redis_table DELETE WHERE key='1';
|
|
```
|
|
|
|
Truncate:
|
|
|
|
Flush Redis db asynchronously. Also `Truncate` support SYNC mode.
|
|
|
|
```sql
|
|
TRUNCATE TABLE redis_table SYNC;
|
|
```
|
|
|
|
|
|
## Limitations {#limitations}
|
|
|
|
Redis engine also supports scanning queries, such as `where k > xx`, but it has some limitations:
|
|
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)
|
|
2. During the scanning, keys could be created and deleted, so the resulting dataset can not represent a valid point in time.
|