标签：concat http blocking back idle psu saving 同步 ica
Redis支持RDB和AOF两种持久化方式，持久化功能有效避免了因进程退出造成数据丢失的问题。RDB持久化是把当前进程数据生成快照保存到磁盘的过程，触发RDB持久化的过程分为手动和自动触发。
手动触发RDB持久化的操作
1. 手动执行SAVE命令
执行命令：
127.0.0.1:6379> SAVE
OK
日志：
35650:M 18 Jul 18:10:42.795 * DB saved on disk
2. 手动执行BGSAVE命令
执行命令：
127.0.0.1:6379> BGSAVE
Background saving started
日志：
35650:M 18 Jul 18:12:48.613 * Background saving started by pid 39301
39301:C 18 Jul 18:12:48.803 * DB saved on disk
39301:C 18 Jul 18:12:48.805 * RDB: 8 MB of memory used by copy-on-write
35650:M 18 Jul 18:12:48.881 * Background saving terminated with success
BGSAVE是针对SAVE阻塞做的优化，Redis涉及RDB持久化的操作优先使用BGSAVE。
自动触发RDB持久化的机制
1. save相关配置，如save m<seconds> n<changes>，m秒内数据集有n次修改，触发BGSAVE。
配置：
save 900 1
save 300 10
save 60 10000
日志：
89428:M 18 Jul 18:46:49.809 * 10000 changes in 60 seconds. Saving...
89428:M 18 Jul 18:46:49.810 * Background saving started by pid 99472
99472:C 18 Jul 18:46:50.030 * DB saved on disk
99472:C 18 Jul 18:46:50.032 * RDB: 8 MB of memory used by copy-on-write
89428:M 18 Jul 18:46:50.113 * Background saving terminated with success
2. 新建主节点的一个从节点，主节点自动BGSAVE生成RDB文件，发送给从节点。
从节点执行命令：
127.0.0.1:6389> SLAVEOF 127.0.0.1 6379
OK
从节点日志：
99498:S 18 Jul 18:56:27.721 * SLAVE OF 127.0.0.1:6379 enabled (user request from 'id=2 addr=127.0.0.1:55238 fd=6 name= age=210 idle=0 flags=N db=0 sub=0 psub=0 multi=-1 qbuf=0 qbuf-free=32768 obl=0 oll=0 omem=0 events=r cmd=slaveof')
99498:S 18 Jul 18:56:27.829 * Connecting to MASTER 127.0.0.1:6379
99498:S 18 Jul 18:56:27.829 * MASTER <-> SLAVE sync started
99498:S 18 Jul 18:56:27.830 * Non blocking connect for SYNC fired the event.
99498:S 18 Jul 18:56:27.830 * Master replied to PING, replication can continue...
99498:S 18 Jul 18:56:27.830 * Partial resynchronization not possible (no cached master)
99498:S 18 Jul 18:56:27.911 * Full resync from master: 2f949fed88eb2df127e45a4870dce9fe1b37f2b2:1
99498:S 18 Jul 18:56:28.184 * MASTER <-> SLAVE sync: receiving 5241839 bytes from master
99498:S 18 Jul 18:56:28.330 * MASTER <-> SLAVE sync: Flushing old data
99498:S 18 Jul 18:56:28.330 * MASTER <-> SLAVE sync: Loading DB in memory
99498:S 18 Jul 18:56:28.388 * MASTER <-> SLAVE sync: Finished with success
主节点日志：
89428:M 18 Jul 18:56:27.831 * Slave 127.0.0.1:6389 asks for synchronization
89428:M 18 Jul 18:56:27.831 * Full resync requested by slave 127.0.0.1:6389
89428:M 18 Jul 18:56:27.831 * Starting BGSAVE for SYNC with target: disk
89428:M 18 Jul 18:56:27.907 * Background saving started by pid 99508
99508:C 18 Jul 18:56:28.105 * DB saved on disk
99508:C 18 Jul 18:56:28.106 * RDB: 8 MB of memory used by copy-on-write
89428:M 18 Jul 18:56:28.182 * Background saving terminated with success
89428:M 18 Jul 18:56:28.270 * Synchronization with slave 127.0.0.1:6389 succeeded
3. 执行DEBUG RELOAD重新加载Redis时，会触发SAVE操作。
执行命令：
127.0.0.1:6379> DEBUG RELOAD
OK
日志：
35650:M 18 Jul 18:40:22.379 * DB saved on disk
35650:M 18 Jul 18:40:22.433 # DB reloaded by DEBUG RELOAD
4. 执行SHUTDOWN时，会触发SAVE操作。
执行命令：
127.0.0.1:6379> SHUTDOWN
日志：
89428:M 18 Jul 19:08:17.003 # User requested shutdown...
89428:M 18 Jul 19:08:17.003 * Saving the final RDB snapshot before exiting.
89428:M 18 Jul 19:08:17.098 * DB saved on disk
89428:M 18 Jul 19:08:17.098 * Removing the pid file.
89428:M 18 Jul 19:08:17.098 * Removing the unix socket file.
89428:M 18 Jul 19:08:17.098 # Redis is now ready to exit, bye bye...
RDB配置参数总览：
save 900 1
save 300 10
save 60 10000
stop-writes-on-bgsave-error yes
rdbcompression yes
rdbchecksum yes
dbfilename dump.rdb
AOF持久化，以独立日志的方式记录每次写命令，解决了数据持久化的实时性问题。AOF的工作流程包括：append（命令写入），sync（数据同步），rewrite（文件重写）和load（重启加载）。
AOF的rewrite过程可以手动触发，和自动触发。
1. 手动触发
执行命令：
127.0.0.1:6379> BGREWRITEAOF
Background append only file rewriting started
日志：
99615:M 18 Jul 19:44:28.610 * Background append only file rewriting started by pid 99639
99615:M 18 Jul 19:44:28.900 * AOF rewrite child asks to stop sending diffs.
99639:C 18 Jul 19:44:28.900 * Parent agreed to stop sending diffs. Finalizing AOF...
99639:C 18 Jul 19:44:28.900 * Concatenating 0.00 MB of AOF diff received from parent.
99639:C 18 Jul 19:44:28.902 * SYNC append only file rewrite performed
99639:C 18 Jul 19:44:28.903 * AOF rewrite: 4 MB of memory used by copy-on-write
99615:M 18 Jul 19:44:28.923 * Background AOF rewrite terminated with success
99615:M 18 Jul 19:44:28.923 * Residual parent diff successfully flushed to the rewritten AOF (0.00 MB)
99615:M 18 Jul 19:44:28.923 * Background AOF rewrite finished successfully
2. 自动触发
根据下面2个参数自动触发。
auto-aof-rewrite-min-size 64mb，运行AOF重写时，文件最小空间。
auto-aof-rewrite-percentage 100，当前AOF文件空间，和上次重写后AOF文件空间的比值。
AOF配置参数总览：
appendonly yes
appendfilename "appendonly.aof"
appendfsync everysec
no-appendfsync-on-rewrite no
auto-aof-rewrite-percentage 100
auto-aof-rewrite-min-size 64mb
RDB和AOF两种持久化方式对比：
1. RDB生成的是二进制文件，占用空间小，恢复效率高。AOF生成的是遵守Redis序列化协议的文本文件，占用空间大，恢复效率低。
~/keepmoving/6379/data $ file dump.rdb appendonly.aof
dump.rdb: data
appendonly.aof: ASCII text, with CRLF line terminators
2. RDB过程对操作系统造成的负载，一般比AOF要大，RDB是对全量数据集做快照，AOF是将数据集增量追加进日志文件，其解决了数据持久化的实时性。
若感兴趣可关注订阅号”数据库最佳实践”(DBBestPractice).
标签：concat http blocking back idle psu saving 同步 ica
原文地址：http://blog.51cto.com/coveringindex/2147120
