Redis in Practice• Why Redis• How to make Redis Faster• Replication and Sentinel

Chen Huangc.huang@*****.com

Content

• Why Redis Comparison of In-Memory Storages Scenarios Sharding (Parallel Scaling)

• How to make Redis Faster

• Replication and Sentinel

Comparison of In-Memory StoragesRedis Memcached MemSQL

Data Structure Key-Value, List, Hash, Set, Z-Set Key-Value Relational

Concurrency Poor Good Good

Sharding Not Generally Available Yes Yes

Transaction Optimistic Lock CAS No

Scripting Lua No No

Replication Yes Repcached Yes

Persistance Yes MemcacheDB Yes

High Availability Redis Sentinel ? ?

Scenarios

• CacheJava:

Map cache = new LinkedHashMap() { protected boolean removeEldestEntry(Map.Entry eldest)

{ return isTimeout(eldest); }}

Redis:SETEX key timeout value

Scenarios

• List / Queue

Java RedisLinkedList / ArrayDeque List

list.offerFirst(element) LPUSH list element

list.offerLast(element) RPUSH list element

list.pollFirst() LPOP list

list.pollLast() RPOP list

• Session[Servlet API]HttpSession session = req.getSession(); // got by session idObject oldValue = session.getAttribute(key);session.setAttribute(key, newValue);

[Implementation]

Scenarios

Java RedisHashMap<String, HashMap> Hash

map.get(id).get(key); HGET id key

map.get(id).put(key, value); HSET id key value

Scenarios• Session Timeout

[Servlet API]session.set(key, new HttpSessionBindingListener() { public void valueUnbound(HttpSessionBindingEvent event) { // Trigger Timeout Event }});

[Implementation]

Java RedisLinkedHashMap Hash + Sorted Set (ZSet)

Iterator i = map.values().iterator();while (i.hasNext() && isTimeout(i.next())) { // Trigger Timeout Event i.remove();}

ZRANGEBYSCORE zset 0 now// Trigger Timeout EventHDEL id, id, ...ZREMRANGEBYSCORE zset 0 now

Sharding (Parallel Scaling)

• Redis is Single-Threaded• Multiple Redis Instances in one Server• Partition by Hash of Keys

Content

• Why Redis

• How to make Redis Faster Time Complexity Communication Latency Serialization

• Replication and Sentinel

Time Complexity

See Redis Documentation for more Details

Structure Operation ComplexityHash HGET id key

Key-Value GET id

Key-Value KEYS prefix*

List LPUSH/LPOP

List LINDEX/LSET

Sorted Set ZADD

Sorted Set ZRANGEBYSCORE

O(1)

O(1)

O(n)

O(1)

O(n)

O(log(n))

O(log(n)+m)

Communication Latency

• Massive (Multi-Row) Insertion[SQL]

× INSERT INTO cache (key, value) VALUES ("key1", "value1");INSERT INTO cache (key, value) VALUES ("key2", "value2");...

√ INSERT INTO cache (key, value) VALUES ("key1", "value1"),("key2", "value2"), ("key3", "value3"), ...

[Redis]× HSET cache key1 value1

HSET cache key2 value2...

√ HMSET cache key1 value1 key2 value2 ...

Communication Latency

• Pipeline (Batch)

Communication Latency

• Pipeline (Batch)[SQL in Java]

try (Statement stmt = conn.createStatement()) {stmt.addBatch("INSERT INTO cache1 ...");stmt.addBatch("INSERT INTO cache2 ...");stmt.executeBatch();

}

[Redis in Java]Pipeline pl = jedis.pipelined();pl.hset("cache1", "key1", "value1");pl.hset("cache2", "key2", "value2");pl.sync();

Communication Latency

• Scripting[Java]int balance = Integer.parseInt(jedis.get("balance"));if (balance > 100) {

jedis.set("balance", Integer.toString(balance - 100));}

[Lua]local i = tonumber(redis.call('get', 'balance'))if i > 100 then

redis.call('set', 'balance', tostring(i - 100))end

Communication Latency

• SQL Efficiency

Multi-Row Insertion > Batch > Stored Procedure

• Redis Efficiency

Massive Insertion > Pipeline > Scripting

Serialization

Serialization

Serialization

• Kryo vs. Protobuf

Content

• Why Redis

• How to make Redis Faster

• Replication and Sentinel Replication Sentinel Practice with PHP

Replication

Master

Slave-1

Slave-2

Slave-3

Web Server

Write

Sync to

Sync to

Sync toWeb Server

Read

Read

Read

Sentinel

A

B

C

D

X

B

C

D

A

Sentinels Sentinels

Sync from

Sync from

Practice with PHP

Shard 1 Shard 2

Sentinels

Shard 3 Shard 4

Web Server

Config Center

Write

Read

Scheduled Config Sync

Web Server

Web Server

redis.config.php

redis.config.php

redis.config.php

redis.config.php

Scheduled Config Sync

Practice with PHP

References

• Redishttp://redis.io/

• phpredishttps://github.com/phpredis/phpredis