撤消日志分为6个表空间：
innodb_undo_tablespaces = 6
有人知道其中一种文件之后（例如undo004已损坏，现在是0字节的文件）后如何恢复吗？
还有一个名为undo_4_trunc.log的文件，但它也是0字节：
-rw-r----- 1 mysql mysql 1103101952 Jun 19 22:52 undo001
-rw-r----- 1 mysql mysql 964689920 Jun 19 22:52 undo002
-rw-r----- 1 mysql mysql 155004928 Jun 19 22:52 undo003
-rw-r----- 1 mysql mysql 0 Jun 19 22:52 undo004
-rw-r----- 1 mysql mysql 1006632960 Jun 19 22:52 undo005
-rw-r----- 1 mysql mysql 960495616 Jun 19 22:52 undo006
-rw-r----- 1 mysql mysql 0 Jun 19 22:52 undo_4_trunc.log
错误消息不是很有用，因为缺少文件名，但是在strace之后，我发现应该读取的文件为undo_4_trunc.log，如果移动了该文件，则为mysql尝试读取undo004。
error.log看起来像：
2019-06-21T06:08:10.014993Z 0 [Note] InnoDB: Recovering partial pages from the parallel doublewrite buffer at /mnt/data1/mysql-data/xb_doublewrite
2019-06-21T06:08:10.079377Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079428Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079433Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079437Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079462Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079466Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079470Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079473Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079477Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079480Z 0 [Warning] InnoDB: 16384 bytes should have been read. Only 0 bytes read. Retrying for the remaining bytes.
2019-06-21T06:08:10.079483Z 0 [Warning] InnoDB: Retry attempts for reading partial data failed.
2019-06-21T06:08:10.079487Z 0 [ERROR] InnoDB: Tried to read 16384 bytes at offset 0, but was only able to read 0
2019-06-21T06:08:10.079495Z 0 [ERROR] InnoDB: Operating system error number 2 in a file operation.
2019-06-21T06:08:10.079498Z 0 [ERROR] InnoDB: The error means the system cannot find the path specified.
2019-06-21T06:08:10.079513Z 0 [ERROR] InnoDB: If you are installing InnoDB, remember that you must create directories yourself, InnoDB does not create them.
2019-06-21T06:08:10.079518Z 0 [ERROR] InnoDB: File (unknown): 'read' returned OS error 71. Cannot continue operation
2019-06-21T06:08:10.079521Z 0 [ERROR] InnoDB: Cannot continue operation.