dump开始处理 t2 表时，mysqldump 立马报错呢？
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其原因就是 一致性读的胳膊拗不过DDL的大腿：
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Consistent read does not work over certain DDL statements:(一致性读的胳膊拗不过DDL的大腿)
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Consistent read does not work over DROP TABLE, because MySQL cannot use a table that has been dropped and InnoDB destroys the table.
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Consistent read does not work over ALTER TABLE, because that statement makes a temporary copy of the original table and deletes the original table when the temporary copy is built. When you reissue a consistent read within a transaction, rows in the new table are not visible because those rows did not exist when the transaction's snapshot was taken. In this case, the transaction returns an error as of MySQL 5.6.6: ER_TABLE_DEF_CHANGED, “Table definition has changed, please retry transaction”.
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原因：ALTER TABLE, DROP TABLE, RENAME TABLE, TRUNCATE TABLE 这些DDL语句的执行，会导致无法使用undo构造出正确的一致性读，一致性读和它们是无法隔离的。