Redis ndc2013
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Redis Tips discusses various tips for using Redis including dangerous commands to avoid such as KEYS and FLUSHALL. It describes how FLUSHALL works differently in Redis compared to Memcache and can be slow. It also covers Redis memory policies, replication, RDB snapshots, and approaches to sharding or clustering Redis including using a client library or server proxy. Sentinel is introduced as a failover solution for Redis masters and slaves.
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Redis ndc2013
- 2. • OpenSource Contributor • REDIS • TWEMPROXY
- 6. Dangerous Commands •Why? –Single Thread. –Each command should spend small time.
- 7. Keys *• Don’t use keys command in production. –“Warning: consider KEYS as a command that should only be used in production environments with extreme care” is written in redis.io keys commands manual.
- 8. Keys * di = dictGetSafeIterator(c->db->dict); allkeys = (pattern[0] == '*' && pattern[1] == '0'); while((de = dictNext(di)) != NULL) { …… stringmatchlen(pattern,plen,key,sdslen(key),0) }
- 9. FlushAll Cache Item Count Time Memcache 1,000,000 1~2ms Redis 1,000,000 1000ms(1 second)
- 10. FlushAll • Redis’s FlushAll is slow and paused. • But memcache’s flush is really fast. –memcache doesn’t depend on Item count. –Redis depends on Item count.
- 11. FlushAll • What is different from memcache’s flush. • Memcache just sets time to flush. • Redis deletes all items. –It spends 1 second in 1M or 2M items
- 12. FlushAll-Redis long long emptyDb() { for (int j = 0; j < server.dbnum; j++) { dictEmpty(server.db[j].dict); dictEmpty(server.db[j].expires); } return removed; }
- 13. FlushAll-Redis
- 14. FlushAll-Memcachestatic void process_command(conn *c, char *command) { if (exptime > 0) settings.oldest_live = realtime(exptime) - 1; else /* exptime == 0 */ settings.oldest_live = current_time - 1; }
- 15. FlushAll-Memcacheif (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; }
- 16. Redis Memory Policy• Volatile-lru • Allkeys-lru • Volatile-random • Allkeys-random • Volatile-ttl • noeviction
- 17. Redis Memory Policy • In 64bit, Memory Policy doesn’t work, if you don’t set maxmemory parameter. • In 32bit, maxmemory is set 4GB as default
- 18. Default Setting in 64 • There is no memory limitation. • So If you insert bigger data than memory. It will be slow. • But But But. Make sure Vm.overcommit_memory property.
- 19. Memory Policy • If you use Memory-Policy and replication. – It can cause some consistency problem. Master SlaveDelete propagation Delete items because of its own memory policy
- 20. Replication •Support Chained Replication •Common mistake
- 21. Replication •Support Chained Replication Master Slave Slave Slave Slave
- 22. Replication •Common mistake. –Don’t forget “slaveof no one” •Slave’s replicationCron keeps track of master’s health.
- 25. Replication Master Slave replicationCron When master reruns, Resync with Master
- 26. Replication Master Slave replicationCron Slave will has no data after resyncing If master has no data.
- 28. RDB • Good and Bad. • It causes all of problems.
- 29. RDB - GOOD • Can store data into persistent layer.
- 30. 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
- 31. RDB – Large Memory • Performance is relevant to Memory Size. 17.1 GB 34.2 GB 68.4 GB 117 GB
- 32. RDB - BAD • Using bgsave in slave. • Turning off RDB. • Using save in master or slave.
- 33. RDB – Twice Memory • fork() and COW(copy on write) Issue –In Write Heavy System:
- 34. RDB – Twice Memory
- 35. RDB – Twice Memory
- 36. RDB – Twice Memory
- 37. Real Case Study • Background –Can’t write to Redis Server –Sentinel doesn’t find Server’s failure.
- 38. 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.”
- 39. Real Case Studyif (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; }
- 40. 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.
- 41. SELECT Command • Don’t use “SELECT” Command. –You will not be able to use “SELECT” in Redis Cluster. • Redis Proxy can make some troubles.
- 42. Response Time • Why memcache’s response time is uniformed? –Difference of Memory Allocator Memcache Redis - Slab Allocator - Just malloc()
- 43. Redis VS Memcache • The popular question –Redis and Memcache: What is better? Memcache Redis - Uniformed Response Time - More stable - Data Structure - Persistent
- 44. Sentinel
- 45. Sentinel • Sentinel is Failover Solution for Redis. Master Slave Sentinel Sentinel periodically checks Redis Master
- 46. Sentinel Master Slave Sentinel Send “slaveof no one” to slave node
- 47. Sentinel Master Slave Sentinel Notify to client about changing master Client
- 48. 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"
- 50. Two Approches.
- 52. Client Library NHN Case Study: http://helloworld.naver.com/helloworld/294797 Craiglist Case Study: http://blog.zawodny.com/2011/02/26/redis- sharding-at-craigslist/
- 53. Client Library ZooKeeper or health Checker Redis Library
- 54. Craigslist
- 55. NHN Application Servers ZooKeeper Redis Cluster Manager Redis Shard-1 Redis Shard-2 Redis Shard-3
- 56. NHN
- 57. Client Library • Benefits –No hob(faster than server proxy) • Liabilities –Consistency Problem(Timing Issue)
- 58. Server Proxy Redis Cloud Services Twemproxy https://github.com/twitter/twemproxy
- 59. Twemproxy • Simple and fast memcache/redis proxy Client Client Client Client Twemproxy Redis Redis Redis Redis
- 60. Twemproxy If you use redis as a store, Twemproxy might not be good for your purpose
- 61. Server Proxy • Benefits –Client doesn’t need any other libraries • Liabilities –Hob.(less speed and proxy is also SPOF)
- 62. Q & A
- 63. Thank you!