# Redis

Remote Dictionary Server，可做為資料庫、快取、訊息代理程式和佇列使用。所有 Redis 資料都位於記憶體內，而資料庫的資料則存放在磁碟或 SSD 上，所以相較起來 Redis 可避免搜尋時間延遲，還能在幾微秒的時間內存取資料，平均讀取和寫入操作時間低於一毫秒，並支援每秒百萬個操作。

## Install

$ brew install redis

## Start

$ redis-server
29316:C 12 Jun 2020 14:29:34.897 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
29316:C 12 Jun 2020 14:29:34.897 # Redis version=6.0.5, bits=64, commit=00000000, modified=0, pid=29316, just started
29316:C 12 Jun 2020 14:29:34.897 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
29316:M 12 Jun 2020 14:29:34.899 * Increased maximum number of open files to 10032 (it was originally set to 256).
                _._
           _.-``__ ''-._
      _.-``    `.  `_.  ''-._           Redis 6.0.5 (00000000/0) 64 bit
  .-`` .-```.  ```\/    _.,_ ''-._
 (    '      ,       .-`  | `,    )     Running in standalone mode
 |`-._`-...-` __...-.``-._|'` _.-'|     Port: 6379
 |    `-._   `._    /     _.-'    |     PID: 29316
  `-._    `-._  `-./  _.-'    _.-'
 |`-._`-._    `-.__.-'    _.-'_.-'|
 |    `-._`-._        _.-'_.-'    |           http://redis.io
  `-._    `-._`-.__.-'_.-'    _.-'
 |`-._`-._    `-.__.-'    _.-'_.-'|
 |    `-._`-._        _.-'_.-'    |
  `-._    `-._`-.__.-'_.-'    _.-'
      `-._    `-.__.-'    _.-'
          `-._        _.-'
              `-.__.-'

29316:M 12 Jun 2020 14:29:34.909 # Server initialized
29316:M 12 Jun 2020 14:29:34.911 * Ready to accept connections

## Usage

### Value

>>> import redis

>>> r = redis.Redis(host='localhost', port=6379)
>>> r.set('foo', 'bar')
True
>>> r.get('foo')
'bar'

### Password

暫時性的方式，重啟後會失效：

$ redis-cli
127.0.0.1:6379> config get requirepass
1) "requirepass"
2) ""

127.0.0.1:6379> config set requirepass password
OK

127.0.0.1:6379> config get requirepass
1) "requirepass"
2) "password"

永久的方式是修改設定檔，重啟 Redis 即生效：

$ vim /usr/local/etc/redis.conf

# requirepass foobared
           ↓
requirepass $(PASSWORD)

## 參考資料

- [Python Redis](https://redislabs.com/lp/python-redis/)
- [Redis quickstart](https://redis.io/topics/quickstart)
- [Try Redis](http://try.redis.io/)
- [Redis Document](https://redis-py.readthedocs.io/en/latest)