一、問題來源

有一個朋友@水米田 問我，基于POSITION的主從。他做了如下的操作

將備份的一些binlog文件加入到了目錄中修改index文件，加入了這些binlog文件flush binary logs然后整個主從環(huán)境大量延遲。

二、朋友的測試

下面是另外一個朋友@徐晨亮的測試：

master上：(root:db1@xucl:10:30:22)[(none)]> show binary logs;+---------------------+-----------+| Log_name | File_size |+---------------------+-----------+| mysql-binlog.000031 | 1019 || mysql-binlog.000032 | 424 || mysql-binlog.000033 | 244 || mysql-binlog.000034 | 2332 || mysql-binlog.000035 | 2134 || mysql-binlog.000036 | 845915 || mysql-binlog.000037 | 11735 || mysql-binlog.000038 | 284 || mysql-binlog.000039 | 284 || mysql-binlog.000040 | 284 || mysql-binlog.000041 | 284 || mysql-binlog.000042 | 234 |+---------------------+-----------+12 rows in set (0.00 sec)(root:db1@xucl:10:30:34)[(none)]> purge binary logs to ’mysql-binlog.000039’;Query OK, 0 rows affected (0.00 sec)(root:db1@xucl:10:30:49)[(none)]> show binary logs;+---------------------+-----------+| Log_name | File_size |+---------------------+-----------+| mysql-binlog.000039 | 284 || mysql-binlog.000040 | 284 || mysql-binlog.000041 | 284 || mysql-binlog.000042 | 234 |+---------------------+-----------+4 rows in set (0.00 sec)執(zhí)行插入數(shù)據(jù)(root:db1@xucl:10:31:23)[xucl]> insert into t values(9,9);將備份的binlog拷貝回原先的目錄并修改index文件進行注冊[root@izbp12nspj47ypto9t6vyez logs]# ll總用量 884-rw-r----- 1 mysql mysql 1019 5月 20 22:03 mysql-binlog.000031-rw-r----- 1 mysql mysql 424 5月 20 22:03 mysql-binlog.000032-rw-r----- 1 mysql mysql 244 5月 20 22:03 mysql-binlog.000033-rw-r----- 1 mysql mysql 2332 5月 20 22:03 mysql-binlog.000034-rw-r----- 1 mysql mysql 2134 5月 20 22:03 mysql-binlog.000035-rw-r----- 1 mysql mysql 845915 5月 20 22:03 mysql-binlog.000036-rw-r----- 1 mysql mysql 11735 5月 20 22:05 mysql-binlog.000037-rw-r----- 1 mysql mysql 284 5月 20 22:06 mysql-binlog.000038-rw-r----- 1 mysql mysql 284 5月 21 10:28 mysql-binlog.000039-rw-r----- 1 mysql mysql 284 5月 21 10:28 mysql-binlog.000040-rw-r----- 1 mysql mysql 284 5月 21 10:28 mysql-binlog.000041-rw-r----- 1 mysql mysql 491 5月 21 10:31 mysql-binlog.000042-rw-r----- 1 mysql mysql 204 5月 21 10:30 mysql-binlog.index主庫flush binary logs(root:db1@xucl:10:32:51)[(none)]> flush binary logs;Query OK, 0 rows affected (0.01 sec)(root:db1@xucl:10:32:57)[(none)]> show binary logs;+---------------------+-----------+| Log_name | File_size |+---------------------+-----------+| mysql-binlog.000031 | 1019 || mysql-binlog.000032 | 424 || mysql-binlog.000033 | 244 || mysql-binlog.000034 | 2332 || mysql-binlog.000035 | 2134 || mysql-binlog.000036 | 845915 || mysql-binlog.000037 | 11735 || mysql-binlog.000038 | 284 || mysql-binlog.000039 | 284 || mysql-binlog.000040 | 284 || mysql-binlog.000041 | 284 || mysql-binlog.000042 | 541 || mysql-binlog.000043 | 234 |+---------------------+-----------+13 rows in set (0.00 sec)此時，slave報錯如下：(root:db1@xucl:10:31:05)[(none)]> show slave statusG*************************** 1. row ***************************Slave_IO_State: Master_Host: 127.0.0.1 Master_User: repl Master_Port: 3306Connect_Retry: 60 Master_Log_File: mysql-binlog.000035 Read_Master_Log_Pos: 194Relay_Log_File: izbp12nspj47ypto9t6vyez-relay-bin.000011Relay_Log_Pos: 373 Relay_Master_Log_File: mysql-binlog.000035 Slave_IO_Running: No Slave_SQL_Running: Yes Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0 Last_Error: Skip_Counter: 0 Exec_Master_Log_Pos: 194 Relay_Log_Space: 648 Until_Condition: NoneUntil_Log_File:Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher:Master_SSL_Key: Seconds_Behind_Master: NULLMaster_SSL_Verify_Server_Cert: NoLast_IO_Errno: 1236Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: ’Cannot replicate GTID-transaction when @@GLOBAL.GTID_MODE = OFF, at file /storage/single/mysql3306/logs/mysql-binlog.000035, position 194.; the first event ’mysql-binlog.000039’ at 234, the last event read from ’/storage/single/mysql3306/logs/mysql-binlog.000035’ at 259, the last byte read from ’/storage/single/mysql33’Last_SQL_Errno: 0Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 3306 Master_UUID: e8bdf01a-c79b-11e8-82b3-00163e088352 Master_Info_File: mysql.slave_master_info SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: 190521 10:32:57 Last_SQL_Error_Timestamp:Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: 4c423515-6661-11e9-b767-00163e088352:1-7,e8bdf01a-c79b-11e8-82b3-00163e088352:1-57192Auto_Position: 0 Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version:1 row in set (0.00 sec)從slave上的報錯來看，在主庫flush binary logs后，從庫又讀取注冊的binlog并且又apply了

三、現(xiàn)象說明

從整個測試來看，MySQL視乎將手動注冊的文件進行了傳輸和應用。報錯是因為這個庫以前是GITD_MODE=ON的，但是測試的時候已經(jīng)關閉了GTID_MODE，改為了POSITION的模式，這個報錯是因為DUMP線程會進行檢測：

這個圖來自我新寫的一個系列（暫時還沒發(fā)布，大概年底才能寫好）。不管怎么說，DUMP線程已經(jīng)在開始傳輸老的binlog文件了。那么原因是什么呢？下面我們將進行解釋。

四、flush binary logs對binlog的操作

flush binary logs 將包含如下操作：

獲取新的binlog文件名字 關閉舊的binlog 關閉index file 打開index file 打開新的binlog 將新的binlog加入到indexfile

具體可以參考函數(shù)MYSQL_BIN_LOG::new_file_impl。其中要說明一下獲取新的binlog文件名字是通過函數(shù)find_uniq_filename實現(xiàn)的，其中包含如下代碼：

file_info= dir_info->dir_entry; for (i= dir_info->number_off_files ; i-- ; file_info++) { if (strncmp(file_info->name, start, length) == 0 && is_number(file_info->name+length, &number,0)) { set_if_bigger(max_found, number); } }... *next= (need_next || max_found == 0) ? max_found + 1 : max_found;

大概意思就是掃描index file文件里面的binlog文件，獲取其序號最高的一個，然后加1。棧幀如下：

#0 find_uniq_filename (name=0x7fffec5ec6d0 '/mysqldata/mysql3340/log/binlog', next=0x7fffec5ec678, need_next=true) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:3679#1 0x000000000187d208 in generate_new_log_name (new_name=0x7fffec5ec6d0 '/mysqldata/mysql3340/log/binlog', new_ext=0x0, log_name=0x7ffedc011520 '/mysqldata/mysql3340/log/binlog', is_binlog=true) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:3767#2 0x0000000001884fdb in MYSQL_BIN_LOG::new_file_impl (this=0x2e83640, need_lock_log=false, extra_description_event=0x0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:7175#3 0x0000000001884cbb in MYSQL_BIN_LOG::new_file_without_locking (this=0x2e83640, extra_description_event=0x0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:7099#4 0x0000000001886b6b in MYSQL_BIN_LOG::rotate (this=0x2e83640, force_rotate=true, check_purge=0x7fffec5ecbfb) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:7775#5 0x0000000001886d53 in MYSQL_BIN_LOG::rotate_and_purge (this=0x2e83640, thd=0x7ffedc000b90, force_rotate=true) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:7846

因此即便我們手動修改了index file，flush binary logs卻不會有問題，因為它實際掃描了index file文件。同時我們也看到flush binary logs重新加載了index file，這個時候手動修改的index file就生效了，使用show binary logs就能查看到你加入的文件了。

五、主從問題的產(chǎn)生

binlog切換后，DUMP線程也需要讀取下一個binlog文件。我們來看看它是怎么確認讀取哪一個文件的。

在函數(shù)sender.run()中可以找到循環(huán)每個binlog文件的代碼。下面一句是尋找下一個binlog文件：

int error= mysql_bin_log.find_next_log(&m_linfo, 0);

mysql_bin_log.find_next_log 包含的代碼：

my_b_seek(&index_file, linfo->index_file_offset);//進行偏移量偏移 linfo->index_file_start_offset= linfo->index_file_offset; length=my_b_gets(&index_file, fname, FN_REFLEN));//讀取文件名字... if(normalize_binlog_name(full_fname, fname, is_relay_log))... linfo->index_file_offset= my_b_tell(&index_file);//偏移量從新記錄以備下一次使用

我們能夠看到DUMP線程并沒有實際掃描整個index文件，而是通過一個index文件的偏移量進行讀取。如果手動修改index文件那么偏移量就出現(xiàn)了錯亂。因此DUMP發(fā)送的下一個文件將是不確定的。因此出現(xiàn)了發(fā)送手動注冊的binlog文件給從庫的現(xiàn)象，這種情況下可能出現(xiàn)下面情況：

如果是GTID_MODE 關閉，使用POSITION那么這種情況一定報錯，比如重復的行。 如果是GTID_MODE 和AUTO_POSITION=1，那么DUMP線程會進行GTID的過濾不發(fā)送，因為Event不發(fā)送所以延遲會持續(xù)一段時間為0。 如果是GTID_MODE 和AUTO_POSITION=0，那么SQL線程應用GITD_EVENT的時候會進行過濾，延遲可能出現(xiàn)很大的情況。

盡管GTID可能可以屏蔽這種問題，但是DUMP線程已經(jīng)在考慮發(fā)送老的binlog文件了，這是不合適的。

六、purge binary logs能夠維護這個偏移量

為什么purge binary logs不會出現(xiàn)問題呢，因為在purge binary logs的語句下，會維護這個偏移量如下：

virtual void operator()(THD *thd) { LOG_INFO* linfo; mysql_mutex_lock(&thd->LOCK_thd_data); if ((linfo= thd->current_linfo))//b binlog.cc:2829 { /* Index file offset can be less that purge offset only if we just started reading the index file. In that case we have nothing to adjust. */ if (linfo->index_file_offset < m_purge_offset) linfo->fatal = (linfo->index_file_offset != 0); else linfo->index_file_offset -= m_purge_offset; } mysql_mutex_unlock(&thd->LOCK_thd_data);

我們可以看到linfo->index_file_offset -= m_purge_offset;這樣一個語句。下面是棧幀：

#0 Adjust_offset::operator() (this=0x7fffec5ec720, thd=0x7ffedc000be0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:2831#1 0x0000000000eef320 in Do_THD::operator() (this=0x7fffec5ec6a0, thd=0x7ffedc000be0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/mysqld_thd_manager.cc:46#2 0x0000000000eefa0f in std::for_each<THD**, Do_THD> (__first=0x3003358, __last=0x3003368, __f=...) at /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algo.h:4200#3 0x0000000000eeefc0 in Global_THD_manager::do_for_all_thd (this=0x3003340, func=0x7fffec5ec720) at /mysqldata/percona-server-locks-detail-5.7.22/sql/mysqld_thd_manager.cc:273#4 0x000000000187ae0a in adjust_linfo_offsets (purge_offset=0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:2873#5 0x0000000001883239 in MYSQL_BIN_LOG::remove_logs_from_index (this=0x2e83640, log_info=0x7fffec5ec7d0, need_update_threads=true) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:6352#6 0x0000000001883676 in MYSQL_BIN_LOG::purge_logs (this=0x2e83640, to_log=0x7fffec5eca80 '/mysqldata/mysql3340/log/binlog.000001', included=false, need_lock_index=true, need_update_threads=true, decrease_log_space=0x0, auto_purge=false) at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:6469#7 0x000000000187b4b5 in purge_master_logs (thd=0x7ffee0000c00, to_log=0x7ffee0006600 'binlog.000001') at /mysqldata/percona-server-locks-detail-5.7.22/sql/binlog.cc:3127

七、測試POSITION模式下的報錯

1、 環(huán)境

mysql> show binary logs;+---------------+-----------+| Log_name | File_size |+---------------+-----------+| binlog.000001 | 198 || binlog.000002 | 154 |+---------------+-----------+2 rows in set (0.00 sec)mysql> show create table testcp G;*************************** 1. row *************************** Table: testcpCreate Table: CREATE TABLE `testcp` ( `id` int(11) NOT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf81 row in set (0.00 sec)ERROR: No query specified

2、執(zhí)行一個語句

主庫：

mysql> insert into testcp values(20);Query OK, 1 row affected (0.43 sec)mysql> select * from testcp;+----+| id |+----+| 10 || 20 |+----+2 rows in set (0.01 sec)

從庫：

mysql> show slave status G;*************************** 1. row ***************************Slave_IO_State: Waiting for master to send event Master_Host: 192.168.99.41 Master_User: repl Master_Port: 3340Connect_Retry: 60 Master_Log_File: binlog.000002 Read_Master_Log_Pos: 417Relay_Log_File: relay.000004Relay_Log_Pos: 624 Relay_Master_Log_File: binlog.000002 Slave_IO_Running: Yes Slave_SQL_Running: Yes...mysql> select * from testcp;+----+| id |+----+| 10 || 20 |+----+

這個時候DUMP線程index file偏移指針如下：

3、主庫執(zhí)行purge binary logs

做之前拷貝原有binlog.000001為binlog.000001bak因為等會要拷貝回去

mysql> purge binary logs to ’binlog.000002’;Query OK, 0 rows affected (3.14 sec)mysql> show binary logs;+---------------+-----------+| Log_name | File_size |+---------------+-----------+| binlog.000002 | 417 |+---------------+-----------+1 row in set (0.00 sec)

因為purge binary logs命令會維護偏移指針，這個時候DUMP線程的index file偏移指針如下：

4、手動更改

將binlog.000001bak拷貝為binlog.000001，然后修改index file將binlog.000001加入回去，然后flush binary logs如下：

mysql> flush binary logs;Query OK, 0 rows affected (0.15 sec)mysql> show binary logs;+---------------+-----------+| Log_name | File_size |+---------------+-----------+| binlog.000001 | 198 || binlog.000002 | 461 |+---------------+-----------+2 rows in set (0.00 sec)

手動完成這個工作并不會維護DUMP線程的index file偏移指針，因此如下：

就這樣DUMP線程重新發(fā)送了一次binlog.000002的內容，POSITION的從庫只能報錯了如下：

mysql> select * from replication_applier_status_by_worker G*************************** 1. row *************************** CHANNEL_NAME: WORKER_ID: 1 THREAD_ID: NULL SERVICE_STATE: OFFLAST_SEEN_TRANSACTION: ANONYMOUS LAST_ERROR_NUMBER: 1062 LAST_ERROR_MESSAGE: Worker 1 failed executing transaction ’ANONYMOUS’ at master log binlog.000002, end_log_pos 386; Could not execute Write_rows event on table testmts.testcp; Duplicate entry ’20’ for key ’PRIMARY’, Error_code: 1062; handler error HA_ERR_FOUND_DUPP_KEY; the event’s master log binlog.000002, end_log_pos 386 LAST_ERROR_TIMESTAMP: 2019-05-21 14:46:26

八、總結

這種操作非常不規(guī)范，如果實在要這么做考慮如下步驟：

關閉全部的從庫 手動注冊binlog文件，修改index 文件 flush binary logs 啟動從庫

這種情況下將會重新初始化DUMP的偏移量指針，應該是沒有問題的。還是盡量不要考慮這么做。

以上就是MySQL手動注冊binlog文件造成主從異常的原因的詳細內容，更多關于MySQL 主從異常的資料請關注好吧啦網(wǎng)其它相關文章！