MySQL slave 延迟一列外键检查和自增加锁

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MySQL slave 延迟一列外键检查和自增加锁

一、现象

延迟大，大事物。

表结构

无IO

SQL THREAD占用CPU 100%

二、pscak 采样

采样30个点

外键检查占70%

自增锁获取占30%

三、自增锁获取逻辑

逻辑如下其实也是innodb_autoinc_lock_mode参数的作用

			
									switch (lock_mode) {

									    case AUTOINC_NO_LOCKING://innodb_autoinc_lock_mode=2

									        /* Acquire only the AUTOINC mutex. */

									        dict_table_autoinc_lock(m_prebuilt->table);

									        break;

									    case AUTOINC_NEW_STYLE_LOCKING: // innodb_autoinc_lock_mode=1 注意这里没有break 巧妙的完成了逻辑

									        /* For simple (single/multi) row INSERTs, we fallback to the

									        old style only if another transaction has already acquired

									        the AUTOINC lock on behalf of a LOAD FILE or INSERT ... SELECT

									        etc. type of statement. */

									        if (thd_sql_command(m_user_thd) == SQLCOM_INSERT

									            || thd_sql_command(m_user_thd) == SQLCOM_REPLACE) {

									            dict_table_t*   ib_table = m_prebuilt->table;

									            /* Acquire the AUTOINC mutex. */

									            dict_table_autoinc_lock(ib_table);

									            /* We need to check that another transaction isn't

									            already holding the AUTOINC lock on the table. */

									            if (ib_table->n_waiting_or_granted_auto_inc_locks) {

									                /* Release the mutex to avoid deadlocks. */

									                dict_table_autoinc_unlock(ib_table);

									            } else {

									                break;

									            }

									        }

									        /* Fall through to old style locking. */

									    case AUTOINC_OLD_STYLE_LOCKING://innodb_autoinc_lock_mode=0 触发

									        DBUG_EXECUTE_IF("die_if_autoinc_old_lock_style_used",

									                ut_ad(0););

									        error = row_lock_table_autoinc_for_mysql(m_prebuilt); //这个函数上表上的自增锁

									        if (error == DB_SUCCESS) {

									            /* Acquire the AUTOINC mutex. */

									            dict_table_autoinc_lock(m_prebuilt->table);

									        }

									        break;

									    default:

									        ut_error;

									    }