xtrabackup原理

通信方式：innobackupex和xtrabackup，这2个工具之间的交互和协调是通过控制文件的创建和删除来实现的，主要文件有：

xtrabackup_suspended_1
xtrabackup_suspended_2
xtrabackup_log_copied

备份过程：

innobackupex 在启动后，会先 fork 一个进程，启动 xtrabackup进程，然后就等待 xtrabackup 备份完 ibd 数据文件；
xtrabackup 在备份 InnoDB 相关数据时，是有2种线程的，一种是 redo 拷贝线程，负责拷贝 redo 文件，一种是 ibd 拷贝线程，负责拷贝 ibd 文件；redo 拷贝线程只有一个，在 ibd 拷贝线程之前启动，在 ibd 线程结束后结束。xtrabackup 进程开始执行后，先启动 redo 拷贝线程，从最新的 checkpoint 点开始顺序拷贝 redo 日志；然后再启动 ibd 数据拷贝线程，在 xtrabackup 拷贝 ibd 过程中，innobackupex 进程一直处于等待状态（等待文件被创建）。
xtrabackup 拷贝完成idb后，通知 innobackupex（通过创建文件），同时自己进入等待（redo 线程仍然继续拷贝）;
innobackupex 收到 xtrabackup 通知后，执行FLUSH TABLES WITH READ LOCK (FTWRL)，取得一致性位点，然后开始备份非 InnoDB 文件（包括 frm、MYD、MYI、CSV、opt、par等）。拷贝非 InnoDB 文件过程中，因为数据库处于全局只读状态，如果在业务的主库备份的话，要特别小心，非 InnoDB 表（主要是MyISAM）比较多的话整库只读时间就会比较长，这个影响一定要评估到。
当 innobackupex 拷贝完所有非 InnoDB 表文件后，通知 xtrabackup（通过删文件），同时自己进入等待（等待另一个文件被创建）；
xtrabackup 收到 innobackupex 备份完非 InnoDB 通知后，就停止 redo 拷贝线程，然后通知 innobackupexredo log 拷贝完成（通过创建文件）；
innobackupex 收到 redo 备份完成通知后，就开始解锁，执行 UNLOCK TABLES；
最后 innobackupex 和 xtrabackup 进程各自完成收尾工作，如资源的释放、写备份元数据信息等，innobackupex 等待 xtrabackup 子进程结束后退出。

在上面描述的文件拷贝，都是备份进程直接通过操作系统读取数据文件的，只在执行 SQL 命令时和数据库有交互，基本不影响数据库的运行，在备份非 InnoDB 时会有一段时间只读（如果没有MyISAM表的话，只读时间在几秒左右），在备份 InnoDB 数据文件时，对数据库完全没有影响，是真正的热备。

InnoDB 和非 InnoDB 文件的备份都是通过拷贝文件来做的，但是实现的方式不同，前者是以page为粒度做的(xtrabackup)，后者是 cp 或者 tar 命令(innobackupex)，xtrabackup 在读取每个page时会校验 checksum 值，保证数据块是一致的，而 innobackupex 在 cp MyISAM 文件时已经做了flush（FTWRL），磁盘上的文件也是完整的，所以最终备份集里的数据文件都是写入完整的。

附：备份过程

This software is published under
the GNU GENERAL PUBLIC LICENSE Version 2, June 1991.

171115 15:29:57 innobackupex_56: Executing a version check against the server...
171115 15:29:57 innobackupex_56: Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_file=/home/mysql/mysql/etc/my.cnf;mysql_read_default_group=xtrabackup;mysql_socket=/home/mysql/mysql/tmp/mysql.sock' as 'root' (using password: YES).
171115 15:29:57 innobackupex_56: Connected to MySQL server
171115 15:29:57 innobackupex_56: Done.
171115 15:29:57 innobackupex_56: Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_file=/home/mysql/mysql/etc/my.cnf;mysql_read_default_group=xtrabackup;mysql_socket=/home/mysql/mysql/tmp/mysql.sock' as 'root' (using password: YES).
171115 15:29:57 innobackupex_56: Connected to MySQL server
171115 15:29:57 innobackupex_56: Starting the backup operation

IMPORTANT: Please check that the backup run completes successfully.
At the end of a successful backup run innobackupex_56
prints "completed OK!".

innobackupex_56: Using server version 5.6.23-baidu-trunk-2.2.2.1-log

innobackupex_56: Created backup directory /home/mysql/opbin/xtrabackup/2017-11-15_15-29-57

171115 15:29:57 innobackupex_56: Starting ibbackup with command: /home/mysql/opbin/xtrabackup/xtrabackup_56 --defaults-file="/home/mysql/mysql/etc/my.cnf" --defaults-group="mysqld" --backup --suspend-at-end --target-dir=/home/mysql/opbin/xtrabackup/2017-11-15_15-29-57 --tmpdir=/home/mysql/mysql --extra-lsndir='/home/mysql/mysql'
innobackupex_56: Waiting for ibbackup (pid=29999) to suspend
innobackupex_56: Suspend file '/home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/xtrabackup_suspended_2'

/home/mysql/opbin/xtrabackup/xtrabackup_56 version 2.1.7 for MySQL server 5.6.15 Linux (x86_64) (revision id: undefined)
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /home/mysql/mysql/var
xtrabackup: using the following InnoDB configuration:
xtrabackup: innodb_data_home_dir = /home/mysql/mysql/var
xtrabackup: innodb_data_file_path = ibdata1:1G:autoextend
xtrabackup: innodb_log_group_home_dir = /home/mysql/mysql/var
xtrabackup: innodb_log_files_in_group = 2
xtrabackup: innodb_log_file_size = 1992294400
>> log scanned up to (20735405)
InnoDB: Allocated tablespace 16, old maximum was 0
[01] Copying /home/mysql/mysql/var/ibdata1 to /home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/ibdata1
>> log scanned up to (20735405)
>> log scanned up to (20735405)
>> log scanned up to (20735405)
>> log scanned up to (20735405)
>> log scanned up to (20735405)
>> log scanned up to (20735405)
>> log scanned up to (20735405)
>> log scanned up to (20735405)
>> log scanned up to (20739120)
>> log scanned up to (20739120)
>> log scanned up to (20742705)
>> log scanned up to (20742705)
>> log scanned up to (20746290)
>> log scanned up to (20746290)
>> log scanned up to (20746290)
>> log scanned up to (20749875)
>> log scanned up to (20749875)
>> log scanned up to (20749875)
>> log scanned up to (20749875)
>> log scanned up to (20749875)
>> log scanned up to (20749875)
>> log scanned up to (20749875)
>> log scanned up to (20749875)
>> log scanned up to (20753460)
>> log scanned up to (20753460)
>> log scanned up to (20753460)
>> log scanned up to (20757778)
[01] ...done
[01] Copying ./percona/checksums.ibd to /home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/percona/checksums.ibd
[01] ...done
[01] Copying ./mysql/innodb_table_stats.ibd to /home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/mysql/innodb_table_stats.ibd
[01] ...done
[01] Copying ./mysql/innodb_index_stats.ibd to /home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/mysql/innodb_index_stats.ibd
[01] ...done
[01] Copying ./mysql/slave_worker_info.ibd to /home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/mysql/slave_worker_info.ibd
[01] ...done
[01] Copying ./mysql/slave_relay_log_info.ibd to /home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/mysql/slave_relay_log_info.ibd
[01] ...done
[01] Copying ./mysql/slave_master_info.ibd to /home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/mysql/slave_master_info.ibd
[01] ...done
>> log scanned up to (20757778)
xtrabackup: Creating suspend file '/home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/xtrabackup_suspended_2' with pid '29999'

171115 15:30:26 innobackupex_56: Continuing after ibbackup has suspended
171115 15:30:26 innobackupex_56: Executing FLUSH TABLES...
171115 15:30:26 innobackupex_56: Executing FLUSH TABLES WITH READ LOCK...
171115 15:30:26 innobackupex_56: All tables locked and flushed to disk

171115 15:30:26 innobackupex_56: Starting to backup non-InnoDB tables and files
innobackupex_56: in subdirectories of '/home/mysql/mysql/var/'
innobackupex_56: Backing up files '/home/mysql/mysql/var//performance_schema/*.{frm,isl,MYD,MYI,MAD,MAI,MRG,TRG,TRN,ARM,ARZ,CSM,CSV,opt,par}' (53 files)
innobackupex_56: Backing up file '/home/mysql/mysql/var//percona/db.opt'
>> log scanned up to (20762096)
innobackupex_56: Backing up file '/home/mysql/mysql/var//percona/checksums.frm'
innobackupex_56: Backing up file '/home/mysql/mysql/var//baidu_dba/db.opt'
innobackupex_56: Backing up file '/home/mysql/mysql/var//baidu_dba/heartbeat.frm'
innobackupex_56: Backing up file '/home/mysql/mysql/var//baidu_dba/heartbeat.MYI'
innobackupex_56: Backing up file '/home/mysql/mysql/var//baidu_dba/heartbeat.MYD'
innobackupex_56: Backing up file '/home/mysql/mysql/var//DB/db.opt'
innobackupex_56: Backing up file '/home/mysql/mysql/var//DB/t6.frm'
innobackupex_56: Backing up file '/home/mysql/mysql/var//DB/t4.frm'
innobackupex_56: Backing up file '/home/mysql/mysql/var//DB/t2.frm'
innobackupex_56: Backing up file '/home/mysql/mysql/var//DB/t7.frm'
innobackupex_56: Backing up file '/home/mysql/mysql/var//DB/t3.frm'
innobackupex_56: Backing up file '/home/mysql/mysql/var//DB/t1.frm'
innobackupex_56: Backing up file '/home/mysql/mysql/var//DB/t5.frm'
innobackupex_56: Backing up files '/home/mysql/mysql/var//mysql/*.{frm,isl,MYD,MYI,MAD,MAI,MRG,TRG,TRN,ARM,ARZ,CSM,CSV,opt,par}' (74 files)
171115 15:30:26 innobackupex_56: Finished backing up non-InnoDB tables and files

171115 15:30:26 innobackupex_56: Executing FLUSH NO_WRITE_TO_BINLOG ENGINE LOGS...
171115 15:30:26 innobackupex_56: Waiting for log copying to finish

xtrabackup: The latest check point (for incremental): '20757778'
xtrabackup: Stopping log copying thread.
.>> log scanned up to (20762096)

xtrabackup: Creating suspend file '/home/mysql/opbin/xtrabackup/2017-11-15_15-29-57/xtrabackup_log_copied' with pid '29999'
xtrabackup: Transaction log of lsn (20735405) to (20762096) was copied.
171115 15:30:27 innobackupex_56: All tables unlocked

innobackupex_56: Backup created in directory '/home/mysql/opbin/xtrabackup/2017-11-15_15-29-57'
innobackupex_56: MySQL binlog position: filename 'mysql-bin.000005', position 9359350
171115 15:30:27 innobackupex_56: Connection to database server closed
171115 15:30:27 innobackupex_56: completed OK!

posted on 2017-11-15 15:34 lovemysql 阅读(178) 评论(0) 编辑收藏举报

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