xtrabackup binary最重要的两个过程是backup和prepare，对应的函数分别是xtrabackup_backup_func()和xtrabackup_prepare_func()，这里做一些阅读代码时的笔记。
xtrabackup backup的线程模型：
1. 一个log拷贝线程；
2. n个ibd文件拷贝线程；
3. 一个io监控线程；
4. 通过suspend_start/suspend_end文件来标注是否启动终止线程；
typedef struct {
datafiles_iter_t *it;
uint num;
uint *count;
os_ib_mutex_t count_mutex;
os_thread_id_t id;
}data_thread_ctxt_t;
数据线程上下文
切换工作目录；
116 /** Set if InnoDB must operate in read-only mode. We don't do any
117 recovery and open all tables in RO mode instead of RW mode. We don't
118 sync the max trx id to disk either. */
xb_set_innodb_read_only() 将innodb设成只读模式
srv_backup_mode=TRUE; 将innodb设成backup模式；
设置innodb的一系列参数
innodb_init_param()
xb_normalize_init_values(void)
修改srv_unix_file_flush_method
根据bp大小，调整srv_max_n_threads参数
1017 /*********************************************************************//**
1018 Initializes the synchronization primitives, memory system, and the thread
1019 local storage. */
srv_general_init()
ut_crc32_init()
xb_filters_init()
2567 /************************************************************************
2568 Initializes the I/O and tablespace cache subsystems. */
xb_fil_io_init(void)
838 /******************************************************//**
839 Initializes the log. */
log_init(void)
585 /*********************************************************************//**
586 Creates the lock system at database start. */
lock_sys_create()
open_or_create_log_file
创建xtrabackup_extra_lsndir/extrabackup_traget_dir
表空间memory cache
fil_system_t* f_system = fil_system;
recv_find_max_checkpoint(&max_cp_group, &max_cp_field)
log_group_read_checkpoint_info(max_cp_group, max_cp_field)
checkpoint_lsn_start/checkpoint_no_start
确认一致的checkpoint状态；
创建XB_LOG_FILENAME文件，写入文件头信息；
创建io_watching_thread;
从checkpoint位置开始copy log文件；
xtrabackup_copy_logfile(checkpoint_lsn_start, FALSE)
log_copying/log_copying_stop
创建日志copy线程
os_thread_create(log_copying_thread, NULL, &log_copying_thread_id);
2591 /****************************************************************************
2592 Populates the tablespace memory cache by scanning for and opening data files.
2593 @returns DB_SUCCESS or error code.*/
xb_load_tablespaces()
挂起，等待XB_FN_SUSPENDED_AT_START文件被删除
xtrabackup_suspend
xb_page_bitmap_init()
根据xtrabackup_parallel设置，创建data_copy_thread_func线程
等待所有data_copy_thread_func线程退出
挂起，等待XB_FN_SUSPENDED_AT_END文件被删除
xtrabackup_suspend
读取最新的checkpoint， 记录在metadata的to_lsn字段；
通过设置log_copying=FALSE && set log_copying_stop，停止log_copying_thread；
创建一个文件XB_FN_LOG_COPIED，通知外部脚本，log_copying_thread已经结束；
写metadata；
prepare_func
1. 切换到xtrabackup_real_target_dir
2. 读取XTRABACKUP_METADATA_FILENAME，获取原信息；
metadata_type
3. xtrabackup_init_temp_log()
4. innodb_init_param()
2670 /************************************************************************
2671 Initialize the tablespace memory cache and populate it by scanning for and
2672 opening data files.
2673 @returns DB_SUCCESS or error code.*/
xb_data_files_init()
应用增量到全量
xtrabackup_apply_deltas()
重设innodb初始化参数
innodb_init_param()
innodb_init()
遍历文件
mtr_start -> mtr_commit
trx_sys_print_mysql_binlog_offset()
将binlog位置信息输出到 xtrabackup_binlog_pos_innodb文件中
xtrabackup_close_temp_log(TRUE)
输出记录metadata_log
backup
$./xtrabackup_56 --defaults-file=/u01/my3928/my.cnf --backup --target_dir=/u01/xianlin.lh/backup_dir/
./xtrabackup_56 version 2.1.8 for MySQL server 5.6.15 Linux (x86_64) (revision id: undefined)
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /u01/my3928/data
xtrabackup: using the following InnoDB configuration:
xtrabackup: innodb_data_home_dir = /u01/my3928/data
xtrabackup: innodb_data_file_path = ibdata1:4G;ibdata2:16M:autoextend
xtrabackup: innodb_log_group_home_dir = /u01/my3928/data
xtrabackup: innodb_log_files_in_group = 4
xtrabackup: innodb_log_file_size = 1073741824
2014-05-05 17:29:35 2ac06bc4a2c0 InnoDB: Using Linux native AIO
xtrabackup: using O_DIRECT
>> log scanned up to (1451746590)
[01] Copying /u01/my3928/data/ibdata1 to /u01/xianlin.lh/backup_dir/ibdata1
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
[01] ...done
[01] Copying /u01/my3928/data/ibdata2 to /u01/xianlin.lh/backup_dir/ibdata2
[01] ...done
[01] Copying ./test/t2.ibd to /u01/xianlin.lh/backup_dir/test/t2.ibd
[01] ...done
[01] Copying ./test/t4.ibd to /u01/xianlin.lh/backup_dir/test/t4.ibd
[01] ...done
[01] Copying ./test/t3.ibd to /u01/xianlin.lh/backup_dir/test/t3.ibd
[01] ...done
[01] Copying ./test/sbtest1.ibd to /u01/xianlin.lh/backup_dir/test/sbtest1.ibd
>> log scanned up to (1451746590)
>> log scanned up to (1451746590)
[01] ...done
[01] Copying ./test/t1.ibd to /u01/xianlin.lh/backup_dir/test/t1.ibd
[01] ...done
[01] Copying ./mysql/innodb_index_stats.ibd to /u01/xianlin.lh/backup_dir/mysql/innodb_index_stats.ibd
[01] ...done
[01] Copying ./mysql/slave_worker_info.ibd to /u01/xianlin.lh/backup_dir/mysql/slave_worker_info.ibd
[01] ...done
[01] Copying ./mysql/innodb_table_stats.ibd to /u01/xianlin.lh/backup_dir/mysql/innodb_table_stats.ibd
[01] ...done
[01] Copying ./mysql/slave_relay_log_info.ibd to /u01/xianlin.lh/backup_dir/mysql/slave_relay_log_info.ibd
[01] ...done
[01] Copying ./mysql/slave_master_info.ibd to /u01/xianlin.lh/backup_dir/mysql/slave_master_info.ibd
[01] ...done
>> log scanned up to (1451746590)
xtrabackup: The latest check point (for incremental): '1451746590'
xtrabackup: Stopping log copying thread.
.>> log scanned up to (1451746590)
xtrabackup: Transaction log of lsn (1451746590) to (1451746590) was copied.
创建备份的流程
1 backup_type = full-backuped
2 from_lsn = 0
3 to_lsn = 1451746590
4 last_lsn = 1451746590
5 compact = 0
prepare
$./xtrabackup_56 --defaults-file=/u01/my3928/my.cnf --prepare --target-dir=/u01/xianlin.lh/backup_dir/
./xtrabackup_56 version 2.1.8 for MySQL server 5.6.15 Linux (x86_64) (revision id: undefined)
xtrabackup: cd to /u01/xianlin.lh/backup_dir/
xtrabackup: This target seems to be not prepared yet.
xtrabackup: xtrabackup_logfile detected: size=2097152, start_lsn=(1451746590)
xtrabackup: using the following InnoDB configuration for recovery:
xtrabackup: innodb_data_home_dir = ./
xtrabackup: innodb_data_file_path = ibdata1:4G;ibdata2:16M:autoextend
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 1
xtrabackup: innodb_log_file_size = 2097152
2014-05-05 18:38:32 2b7f2f5202c0 InnoDB: Using Linux native AIO
xtrabackup: using the following InnoDB configuration for recovery:
xtrabackup: innodb_data_home_dir = ./
xtrabackup: innodb_data_file_path = ibdata1:4G;ibdata2:16M:autoextend
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 1
xtrabackup: innodb_log_file_size = 2097152
2014-05-05 18:38:32 2b7f2f5202c0 InnoDB: Using Linux native AIO
xtrabackup: Starting InnoDB instance for recovery.
xtrabackup: Using 104857600 bytes for buffer pool (set by --use-memory parameter)
InnoDB: The InnoDB memory heap is disabled
InnoDB: Mutexes and rw_locks use GCC atomic builtins
InnoDB: Compressed tables use zlib 1.2.3
InnoDB: Using Linux native AIO
InnoDB: Using CPU crc32 instructions
InnoDB: Initializing buffer pool, size = 100.0M
InnoDB: Completed initialization of buffer pool
InnoDB: Highest supported file format is Barracuda.
InnoDB: The log sequence numbers 552524932 and 552524932 in ibdata files do not match the log sequence number 1451746590 in the ib_logfiles!
InnoDB: Database was not shutdown normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages
InnoDB: from the doublewrite buffer...
InnoDB: Last MySQL binlog file position 0 26767310, file name mysql-bin.000023
InnoDB: 128 rollback segment(s) are active.
InnoDB: Waiting for purge to start
2014-05-05 18:38:33 2b7f49056700 InnoDB: Warning: table 'test/sbtest1'
InnoDB: in InnoDB data dictionary has unknown flags 50.
InnoDB: 5.6.15 started; log sequence number 1451746590
[notice (again)]
If you use binary log and don't use any hack of group commit,
the binary log position seems to be:
InnoDB: Last MySQL binlog file position 0 26767310, file name mysql-bin.000023
xtrabackup: starting shutdown with innodb_fast_shutdown = 1
InnoDB: FTS optimize thread exiting.
InnoDB: Starting shutdown...
InnoDB: Shutdown completed; log sequence number 1451747281
prepare的流程：
1 backup_type = full-prepared
2 from_lsn = 0
3 to_lsn = 1451746590
4 last_lsn = 1451746590
5 compact = 0