[MySQL Bug] 在RBR复制模式下使用Merge引擎导致备库Crash的bug-Mysql Tutorial-php.cn

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[MySQL Bug] 在RBR复制模式下使用Merge引擎导致备库Crash的bug

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Jun 07, 2016 pm 05:15 PM

[MySQL Bug] 在RBR复制模式下使用Merge引擎导致备库Crash的bug,而在table_def::compatible_with中：can_convert_field_to(field,

最近碰到一个很蛋疼的BUG，使用merge引擎，row模式下复制，极大的概率crash备库。

我的测试环境是5.1的主库，5.5的备库

test case：

crash的原因非常简单，实际上在很早之前这个bug就fix了(MySQL Bug#47103)，可能是官方疏忽，又或者是Merge存储引擎用的人少，没有将这个patch backport到5.5中。

以下是个简单的介绍。

我们知道每个Binlog的行事件都有一个table_map_event。

在函数Table_map_log_event::do_apply_event中，会根据table map event的内容初始化table_list结构体，并构建table_list->m_tabledef。

这里的table_list->m_tabledef.m_field_metadata是被分配内存的。然后将该table_list挂到rli->tables_to_lock上

而在函数Rows_log_event::do_apply_event中，当调用open_and_lock_tables实际打开表时，还会打开相依赖的子表，并将这些table_list挂到rli->tables_to_lock之后(链接指针为next_global)，但要注意，这里打开的依赖字表时，其table_list->m_tabledef.m_field_metadata实0x0，并没有分配空间

随后，在打开表后，要检查table map里的定义和实际打开表的定义是否相容。

而在table_def::compatible_with中：

can_convert_field_to(field, type(col), field_metadata(col), rli, m_flags, &order)

其中type和field_metadata都会涉及到对m_field_metadata的引用，，因此直接产生段错误，导致crash。

官方的fix见

linux

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