Redis begins

transcript

Redis Begins

charsyam@naver.com

Redis?

Redis? Redis is an open source.

http://redis.io

Redis? Redis is an open source. BSD licensed.

http://redis.io

Redis? Redis is an open source. BSD licensed. advanced key-value store.

http://redis.io

Redis? Redis.io

http://redis.io

Why Redis?

Why Redis? Simple. Performance.

Build $ make

But You can meet some errors in Linux Solution: $> make distclean; make;

Why? Redis saves settings to .make-* files And they disturb normal building.

Argenda Single Thread. Collections. Persistent. Replication.

The one thing you should know.

Redis is Single Threaded!

Single Thread Means!

Don’t execute long task.

Example: Keys command Flushall/flushdb command

Keys *

di = dictGetSafeIterator(c->db->dict); allkeys = (pattern[0] == '*' && pattern[1] == '\0'); while((de = dictNext(di)) != NULL) { …… stringmatchlen(pattern,plen,key,sdslen(key),0) }

FlushAll

Cache Item Count Time

Memcache 1,000,000 1~2ms

Redis 1,000,000 1000ms(1 second)

Memcache’s flush is faster than Redis’s flush.

Memcache’s flush is faster than

Redis’s flush?

FlushAll-Redis for (i = 0; i < ht->size && ht->used > 0; i++) { dictEntry *he, *nextHe; if ((he = ht->table[i]) == NULL) continue; while(he) { nextHe = he->next; dictFreeKey(d, he); dictFreeVal(d, he); zfree(he); ht->used--; he = nextHe; } }

FlushAll-Memcache

if (exptime > 0) settings.oldest_live = realtime(exptime) - 1; else /* exptime == 0 */ settings.oldest_live = current_time - 1;

FlushAll-Memcache if (settings.oldest_live != 0 && settings.oldest_live <= current_time && it->time <= settings.oldest_live) { do_item_unlink(it, hv); do_item_remove(it); it = NULL; }

Collections Memcached supports just K-V List Set Sorted Set Hash

Key:Value $> set key value $> get key

Key:Value sql> insert into userinfo (name, email) values(‘charsyam’, ‘test@abc.com’);

Key:Value $> set id:name “charsyam” $> set id:email test@abc.com $> mget id:name id:email 1) “charsyam” 2) test@abc.com”

List $> rpush listname a --- (a) $> rpush listname b --- (a, b) $> lpush listname c --- (c, a, b) $> rpop listname(or lpop listname)

List - when When you need job queue or stack.

Set $> sadd setname id1 $> sadd setname id2 $> smember setname 1) “id2” 2) “id1”

set - when When you need follwers ids or group members id

Sorted Set $> zadd zsetname 1 “one” $> zadd zsetname 2 “two” $> zadd zsetname 3 “three”

Sorted Set $> zrange zsetname 0 -1 1) “one” 2) “two” 3) “three”

zset - when When you need ranking

Sorted Set $> zrange zsetname 1 3 1) “two” 2) “three”

Hash sql> insert into userinfo (name, email) values(‘charsyam’, ‘test@abc.com’);

Hash $> hmset id name “charsyam” email test@abc.com

Hash $> hgetall 1) “name” 2) “charsyam” 3) “email” 4) “test@abc.com”

Hash $> hset id email abc@abc.com $> hgetall 1) “name” 2) “charsyam” 3) “email” 4) “abc@abc.com”

Remember!!!!!

The one thing you should know.

Don’t insert too many items into collections.

Delete collections

Item Count Time

list 1,000,000 1000ms(1 second)

Sorted set

Redis can store its memory snapshot.

RDB is not Relation DBMS.

RDB is redis snapshot name.

Fork()

RDB - BAD • Bad Performance in Large memory.

• Twice memory problem.

• Denying write problem when storing RDB fails.

• If you just want Cache. Turn off RDB

RDB – Large Memory • Performance is relevant to Memory

17.1 GB 34.2 GB

68.4 GB

117 GB

RDB – Twice Memory • fork() and COW(copy on write) Issue

–In Write Heavy System:

RDB – Twice Memory

Real Case Study • Background

–Can’t write to Redis Server

–Sentinel doesn’t find Server’s failure.

Real Case Study • Reason –If redis fails to save RDB, Redis basically

denies write operations from client.

–“MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk. Commands that may modify the data set are disabled. Please check Redis logs for details about the error.”

Real Case Study • Reason if (server.stop_writes_on_bgsave_err &&

server.saveparamslen > 0 && server.lastbgsave_status == REDIS_ERR && c->cmd->flags & REDIS_CMD_WRITE) { flagTransaction(c); addReply(c, shared.bgsaveerr); return REDIS_OK; }

Real Case Study • Solution #1

• Solution #2

config set stop-writes-on-bgsave-error no

Turn off RDB Setting

2.6.12 부터 conf 에서 stop-writes-on-bgsave-error 설정이 가능해짐.

AOF is append only file.

AOF memorizes all requests.

AOF *3\r\n$3\r\nset\r\n$1\r\nA\r\n$3\r\n123\r\n*3\r\n$3\r\nset\r\n$1\r\nB\r\n$3\r\n123\r\n*3\r\n$3\r\nset\r\n$1\r\nC\r\n$3\r\n123\r\n

AOF *3 $3 Set $1 A ……

AOF Rewrite When size of AOF grows than redis rewrite memory state to AOF.

Redis support master/slave replication

Replication •Support Chained Replication

Master 1st Slave 2nd Slave

1st slave is master of 2nd slave

Replication

Master Slave replicationCron

Health check

Replication

Health check

Replication

When master reruns, Resync with Master

Mistake: Replication

Slave will has no data after resyncing

If master has no data.

Initial Replication Step

Replication Don’t forget “slave of no one”

Sentinel

Sentinel • Sentinel is Failover Solution for Redis.

Master Slave

Sentinel Sentinel periodically checks Redis Master

Sentinel

Master Slave

Sentinel Send “slaveof no one” to slave node

Sentinel

Master Slave

Sentinel Notify to client about changing master

Client

Sentinel redis 127.0.0.1:2003> psubscribe * Reading messages... (press Ctrl-C to quit) 1) "pmessage" 2) "*" 3) "+switch-master" 4) "resque 127.0.0.1 1999 127.0.0.1 2002"

Sentinel • Sentinel will connect correct master

even if you set slave’s ip in conf

Master Slave

Sentinel Slave’s ip in sentinel.conf

Sentinel • INFO

# Replication

role:slave

master_host:127.0.0.1

master_port:6379

……

Sentinel • Reconnect to correct master using

master_host and master_port.

Master Slave

Sentinel Reconnect to master of slave.

Sentinel.conf port 26379

sentinel monitor mymaster 127.0.0.1 6379 1 sentinel down-after-milliseconds mymaster 30000

sentinel can-failover mymaster yes

sentinel parallel-syncs mymaster 1

sentinel failover-timeout mymaster 900000

Wrap Up

Thank you!

Redis begins

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