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公眾號 MySQL學習

隨便記錄點 5.7.22程式碼

MySQL工具主要分為 互動式和非互動式

- 互動式
就是我們平時用的互動式命令方式
- 非互動式（batch mode）
主要用於解析binlog和批次匯入sql，每次都會讀取1行資料到buffer
如果是binlog，那麼每次大約讀取的原始資料為76位元組，及mysqlbinlog解析出來的一行
```
AAAAAAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4AAAAA
AAAAAP4AAAAAAAAAAP4KAAAAAAAAAP4UAAAAAAAAAP4eAAAAAAAAAP4oAAAAAAAAAP4yAAAAAAAA
AP48AAAAAAAAAP5GAAAAAAAAAP5QAAAAAAAAAP5aAAAAAAAAAP4KAAAAAAAAAP4AAAAAAAAAAP4A
AAAAAAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4AAAAA
AAAAAP4AAAAAAAAAAP4AAAAAAAAAAP4KAAAAAAAAAP4UAAAAAAAAAP4eAAAAAAAAAP4oAAAAAAAA
AP4yAAAAAAAAAP48AAAAAAAAAP5GAAAAAAAAAP5QAAAAAAAAAP5aAAAAAAAAAP4KAAAAAAAAAP4A
```
類似這裡就有6行。如果是大事務，每次解析76位元組，add_line 函式。然後等待大事務所有行解析完成後進行com_do函式進行執行命令。
如果是sql語句，那麼就是一條sql執行一次沒有什麼問題。

最近遇到mysqlbinlog|mysql大事務特別慢的情況，因此提交了如下問題：
https://bugs.mysql.com/bug.php?id=102278
8.0.13修復了，5.7.33最新版本依舊存在這個問題。

```
Hi:
  we use mysqlbinlog|mysql to parse binlog and recover binlog,when have large trasaction,mysql client tool
is very slow at add_line function.
  20M trasaction event mysql add line use 1 hour!! cpu is 100% use in sy% and pstack mysql client stack like:

__memmove_sse3
my_realloc
String::mem_realloc
add_line
read_and_execute
main

when batch mode,mysql every time add 76 bytes event line to buffer,buffer init 520 bytes,when 20M event load in 
buffer then call com_do funcation to execute command。

Breakpoint 9, add_line (buffer=..., line=0xa603e0 "/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=1*/;", line_length=45, in_string=0x7fffffffe287 "", ml_comment=0x7fffffffe286, truncated=false)
    at /opt/percona-server-locks-detail-5.7.22/client/mysql.cc:2533
2533      bool need_space= 0;
(gdb) p buffer.m_length
$20 = 0
(gdb) p buffer.m_alloced_length
$21 = 520

when buffer is smaller, every time allocate 4K mem:

if (buffer.length() + length >= buffer.alloced_length())
      buffer.mem_realloc(buffer.length()+length+IO_SIZE);

this step rise frequently mem allocate.and cpu sy% is very high!! 
when mysql use batch mode can we use large init buffer or give our a parameter to control this.
when i search bug i find Bug #85155 is like this,is this fix at mysql 8.0.13,what 5.7 version fix this?

thanks!!
```

我進行了一下修改，如下：
```
mysql.cc main函式下
MAX_BATCH_BUFFER_SIZE 已經定義好為1G

glob_buffer.mem_realloc(MAX_BATCH_BUFFER_SIZE);

[root@mgr3 client]# /opt/my_mysql/bin/mysqlbinlog /opt/bin/log_bin.000002 |/opt/my_mysql/bin/mysql
速度極快了
[root@mgr3 client]# /opt/my_mysql/bin/mysqlbinlog /opt/bin/log_bin.000002 |/opt/my_mysql/bin/mysqlbak
CPU 99%
位於192.168.1.63 上的/opt/my_mysql/bin/mysqlbak目錄下，如果再次遇到這種問題，可以使用修改過的進行執行。

```

MySQL:MySQL工具以及5.7mysqlbinlog|mysql速度極慢問題

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