page cache
Relay log: hard disk
redo log buffer
binlog: fsync
Dump thread
redo log prepare: fsync
Client
Commit OK
写入Relay log
Commit
redo log prepare: write
binlog cache
Sending binlog
binlog: write
hard disk
redo log commit: write
Master
SQL thread: 执行 relay log
读取 binlog
Slave
ACK: Relay log已写完
ACK from Slave
IO thread
