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现象

mysqld突然崩溃，错误日志 Attempting backtrace. You can use the following information to find out where mysqld died. If you see no messages after this, something went terribly wrong... stack_bottom = 7fd06c41be28 thread_stack 0x40000 /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(my_print_stacktrace+0x35)[0x8e37d5] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(handle_fatal_signal+0x41b)[0x651d0b] /lib64/libpthread.so.0(+0xf500)[0x7fd1c9b2d500] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(_Z9get_fieldP11st_mem_rootP5Field+0x43)[0x769b43] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld[0x6768cc] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(_Z11mysql_grantP3THDPKcR4ListI11st_lex_userEmbb+0x4f1)[0x6785c1] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(_Z21mysql_execute_commandP3THD+0x4972)[0x6db4a2] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(_Z11mysql_parseP3THDPcjP12Parser_state+0x531)[0x6dbb71] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(_Z16dispatch_command19enum_server_commandP3THDPcj+0x1782)[0x6dd392] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(_Z24do_handle_one_connectionP3THD+0x10d)[0x6a572d] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(handle_one_connection+0x42)[0x6a5862] /opt/udb/program/mysql/mysql-5.6.20/bin/mysqld(pfs_spawn_thread+0x127)[0xaf8d87] /lib64/libpthread.so.0(+0x7851)[0x7fd1c9b25851] /lib64/libc.so.6(clone+0x6d)[0x7fd1c8b9590d]

原因分析

通过错误查看到(_Z11mysql_grantP3THDPKcR4ListI11st_lex_userEmbb+0x4f1)，mysql_grant函数调用导致崩溃，猜测是用户授权时出了问题，重新登录db发现user表结构确实有问题，下图中1是崩溃后的表结构，2是该mysqld版本对应的user表结构

故障模拟

1 新建一个正常的db，表结构应该是上图中的2 2 删除user表，新建表结构1 3 执行grant语法创建一个新账户，这时mysqld就崩溃了

改进措施

1 任何跨版本导入数据，一定要执行mysql_upgrade 2 有些情况下mysql_upgrade还不一定够用，需要额外再去检查系统表有无问题，故障案例参见 http://blog.csdn.net/cug_jiang126com/article/details/51602757