Redis Inside(1)

Basic

Redis supports lots of data types:

1. string
2. list
3. set
4. hash (k-v map)
   etc.
   Examples:

   redis 127.0.0.1:6379> SET tutorialspoint redis 
   OK 
   redis 127.0.0.1:6379> GET tutorialspoint 
   "redis"

Single Machine Redis

1. Redis keeps a key-value db structure internally. Normally, it is stored in memory. But it also has persistence strategy:
   • RDB: store the compress the k-v db into disk
   • AOF: store change log of cmd
2. a single machine redis can operate multiple dbs. (in a distributed mode, a redis can only operate one db)
3. server logic:
   • handle IO event (client request) and time event. It is event driven.
   • Reactor pattern
   • Single thread

Distributed Redis

1. Support Master-Slave mode. (Master will sync up its data with slave)
2. Use Sentinel will monitor Master health
3. Each node in the cluster will maitain the current cluster state: including some health tag, shard-to-slot mapping
4. Node(shard): responsible for a number of slots. Each node has only one db
   • key send to node A
   • node A check if the key is in its slots
   • if no, return the target node
   • if yes, execute the cmd (find the key’s value or insert the k-v into its db)

Other features

1. Lua
   • reduce network cost. We can do multiple cmds in the lua scripts so one request is only needed to do the same
   • atomic in a lua. No other cmds will be executed in the middle of lua
   • we can reuse the lua script in the client any time.
2. Pub-Sub
   • support simple regex pattern match to topics
   • If subscribers are not online, the message will lost

Use cases

1. find top K hot XXXX in a website
2. find recent visited records
3. sanity check of a request (i.e., if the user id is marched with some fields)
4. statistic: i.e., count how many users are registered, how many visited, etc.