This document summarizes the features, architecture, administration, capacity forecasting, replication, persistence, and table design concepts of Redis. Key points include Redis' data structures of strings, lists, hashes and sets; its single-threaded model with auxiliary threads; persistence via snapshots to disk and AOF logging; master-slave replication topology without resume of broken transfers; and example user login data modeled as keys and indexes in Redis.

1. redis 深入浅出

2. Agenda

Feature&Architecture

Admin&capcity forecast

Replication

Presistence

Table design

3. Feature
redis memcached
data structure string|list|hash|set|zset string
thread model third(main thread, two many
auxiliary thread)
demultiplexer ae.c libevent(3rd library)
persistence yes no
replication yes no
design weak no

4. String

Set hello world

Set hello 1234567

Set hello 1234

5. List

Lpush list aaaa bbb ccc

Double link list, so can lpush,rpush,lpop,rpop

6. Zipmap
Hset test hello world
Hset test aliyun dba
Zipmap defect:Zmlen one bytes, only 253 subkey

7. Architecture

8. Rehash

9. Cache forecast
string 类型的内存大小 = 键值个数 * (dictEntry 大
小 + redisObject 大小 + 包含 key 的 sds 大小 +
包含 value 的 sds 大小 ) + bucket 个数 * 4
zipmap 类型的内存大小 = hashkey 个数 *
(dictEntry 大小 + redisObject 大小 + 包含 key
的 sds 大小 + subkey 的总大小 ) + bucket 个数 *
4
Jemalloc size class

10. Admin

Redis.conf(static), config set(dynamic)
– maxmemory <bytes>
– Appendfsync everysec(fsync pagecache to disk)
– hash-max-zipmap-entries 512
– hash-max-zipmap-value 64

11. Replication

procedure

map

Master slave – slave – slave - slave

defects

Without resume broken transfer

Without lag(slave position)

12. replication

13. Persistence

Snapshot

Fork process, loop hash table, save file dump.rdb

Yes!!! sequential write

Write dump.rdb need O_DIRECT

Aof

Like binlog, for recover after crash

Auto bgrewrteaof

Auxiliary threads

Postpone fsync

14. Auxiliary thread

15. Table desgin login user

Design a login user system

Heap table

userid login_times last_login_time

1 5 2011-1-1

2 1 2011-1-2

3 2 2011-1-3

Last login man? Create index on last_login_time

Max login man? Create index on login_times

Index, explan plan, compute statistics is suck!!!

16. Login user

data

Set userid:1:login_times 5

Set userid:2:login_times 1

Set userid:3:login_times 2

Set userid:1:last_login 2011-1-1

Set userid:2:last_login 2011-1-2

Set userid:3:last_login 2011-1-3

Last login

lpush user_last_login 1

lpush user_last_login 2

lpush user_last_login 3

ltrim user_last_login 0 1

17. Login user

Max login man

zadd user:login_times 5 1

zadd user:login_times 1 2

zadd user:login_times 2 3

zcard user:login_times

zrangebyscore user:login_times 3 +inf withscores

Column store data?

18. Suitable Scene

轻量级的高性能消息队列服务 , 生产者消费者

跨机器的共享内存

Redis 的主要缺点是数据库容量受到物理内存
的限制，不能用作海量数据的高性能读写，并
且它没有原生的可扩展机制，不具有
scale （可扩展）能力，要依赖客户端来实现
分布式读写，因此 Redis 适合的场景主要局限
在较小数据量的高性能操作和运算上。

19. QA
@hoterran
www.hoterran.info