MySQL 8.0 OCP 1Z0-908 1-20题

Q1.Examine this command, which executes successfully:
mysqlbackup --user=dba --password --port=3306 --with-timestamp --backup-dir=/export/backups backup-and-apply-log
Which statement is true?

//每次备份都会新建一个链接

A)The backup accesses the MySQL server files by using a pre-existing connection

备份不会改变数据库的状态

B)The database server is put into a read-only state for the duration of the backup.

该备份为热备，不会将innodb offline

C)An offline backup of InnoDB tables is taken.

备份期间会获取备份锁，所以如果又DDL操作，那么备份将会受到影响，所以该答案为正确
D)The backup can be impacted when DDL operations run during the backup.
Answer:D

mysqlbackup大致的备份过程，可以参考https://teacherwhat.blog.csdn.net/article/details/131866642

Q2.You reconfigure and start a slave that was not replicating for several days.
The configuration file and CHANGE MASTER command are correct. Examine the GTID information from both
master and slave:
Master:
Gtids_executed: aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa:1-321,
 bbbbbbbb-bbbb-bbbb-bbbbbbbbbbbb:1-50,
 Cccccccc-cccc-cccc-cccc-cccccccccccc:1234-1237
Gtids_purged: aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa:1-100,
bbbbbbbb-bbbb-bbbb-bbbbbbbbbbbb:1-10,
 cccccccc-cccc-cccc-cccc-cccccccccccc:1234-1237
Slave:
Gtids_executed: aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa:1-160,
 cccccccc-cccc-cccc-cccc-cccccccccccc:1234-1237
Gtids_executed: aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa:1-70,
 cccccccc-cccc-cccc-cccc-cccccccccccc:1234-1237

可以看到主节点当前异质性的GTID为
aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa:1-321,
bbbbbbbb-bbbb-bbbb-bbbbbbbbbbbb:1-50,
Cccccccc-cccc-cccc-cccc-cccccccccccc:1234-1237
已经由于binlog被删除或者手动purge或者其他原因丢弃的gtid为：
aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa:1-100,
bbbbbbbb-bbbb-bbbb-bbbbbbbbbbbb:1-10,
cccccccc-cccc-cccc-cccc-cccccccccccc:1234-1237
可以看到从节点当前已执行的GTID中，关于aaa-xxx-xxxaaaa的gtid在1-160，所以主节点还保存着160之后的gtid，所以这个事务中的复制不会失败，也不会丢失数据
ccc中的和主节点的一致，也不会有什么问题

但是bbb中的在主节点已执行，在从节点没有执行，而且bbbb已经purge了1-10的事务，所以bbb上的事务会在从节点上丢失，导致主从复制失败
所以选A

Which statement is true?
A)Replication will fail because the master does not have the required transaction with bbbbbbbb-bbbb-bbbb-bbbbbbbbbbbbbbbb GTIDs in its binary logs.
B)Replication will fail because the master has already purged transactions with cccccccc-cccc-cccc-cccc-cccccccccc
GTIDs.
C)Replication will fail because of inconsistent numbers in cccccccc-cccc-cccc-cccc-cccccccccccc GTIDs.
D)Replication will fail because the slave has purged more aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa transactions than the
master.
F)Replication will work.
Answer:A

Q3.Which two authentication plugins require the plain text client plugin for authentication to work?
A)Windows Native authentication
B)PAM authentication
C)LDAP SASL authentication
D)LDAP authentication
E)SHA256 authentication
F)MySQL Native Password
Answer:BD

MySQL 8.0 中，以下两个认证插件需要明文客户端插件（如 mysql_clear_password）才能进行认证：

• B) PAM authentication：PAM（Pluggable Authentication Modules）认证插件需要客户端以明文形式发送密码，因此需要使用明文客户端插件。

• D) LDAP authentication：LDAP 认证插件在某些情况下也需要客户端以明文形式发送密码，因此需要明文客户端插件支持

MySQL :: MySQL 8.0 Reference Manual :: 8.4.1.4 Client-Side Cleartext Pluggable Authentication

Q4.You want to log only the changes made to the database objects and data on the MySQL system. Which log will do this by defaul？

只记录数据对象和数据的更改，所以是binlog

A)error log
B)slow query log
C)general query log
D)binary log
E)audit log
Answer:D

Q5.You have an installation of MySQL 8 on Oracle Linux. Consider the outputs:
Mysql>SHOW GLOBAL VARIABLES
 WHERE Varisble_name=’tmpdir ‘
 OR Variable_name =’ tmp_table_size;
+------------------+-----------+
| Variable_name |Value |
+------------------------+-----+
|tmp_tabe_size | 16777216|
|tmpdir | /tmp |
+-------------------+----------+
Shell>cd/var/lib/mysql
Shell>ls -1|grep temp
Drwxr-x---.2 mysql mysql 4096 Dec 11 14:05 #innodb_temp
Which statement is true about disk temporary tables for this installation?
A)Temporary tables are created in tmpdir only if configured to use MyISAM。
B)Temporary tables are created in tmpdir only after they reach tmp_table_size.
C)Temporary tables will use the InnoDB temporary tablespace located in datadir.
D)Only internal temporary tables from the optimizer will be created in tmpdir.
E)Temporary tables will use the InnoDB temporary tablespace located in /tmp.
Answer:C

超过tmp_table_size 和 max_heap_table_size 最小值的临时表创建到磁盘上。 Tmpdir目录下创建的是临时文件，默认是/tmp
InnoDB用户创建的临时表和磁盘上的内部临时表是在MySQL数据目录中名为ibtmp1的临 时表空间文件中创建的，是全局临时表空间。#innodb_temp 目录下是会话临时表空间 参见官方文档: 15.6.3.5 Temporary Tablespaces 在另外一个题库里选两个，就加上A。

此处引用如下链接：MySQL 8.0 OCP（1Z0-908）中文题库解析-CSDN博客

Q6.Which two actions will secure a MySQL server from network-based attacks?
A)Use MySQL Router to proxy connections to the MySQL server.
B)Place the MySQL instance behind a firewall.防火墙做网络防护
C)Use network file system (NFS) for storing data.
D)Change the listening port to 3307.
E)Allow connections from the application server only.从权限上限制连接的IP
Answer:BE

Q7.Examine the command, which execute successfully:
shell> mysqld --initialize-insecure
Which statement is true?
A)The installation creates a temporary test environment with data in the /tmp directory.
B)The installation is created without enforcing or generating SSL certificates.
C)The root password is created in the error log in plain text.
D)The root password is not created allowing easy access from the same host.
E)The root password is not created allowing easy access from the same host.
Answer:D

//--initialize-insecure初始化完成后默认root密码为空
//mysqld --initialize 命令用于在首次安装后初始化数据目录，包括创建系统表和设置root用户密码

Q8.Examine this command:
shell> mysqldump --no-create-info --all-databases --result-file=dump.sql
Which statement is true?
A)It will not write CREATE TABLESPACE statements.
B)It will not write CREATE LOGFILE GROUP statements.
C)It will not write CREATE TABLE statements.
D)It will not write CREATE DATABASE statements.
Answer:C

//不导出创建表sql(默认存在)，即不导出表结构，只导出数据

Q9.The mysqld instance has the connection control plugin enabled with these settings:
Connection_control_min_connection_delay=1000
Connection_control_max_connection_delay=2000
The minimum and maximum delays need to be increased to 3000 and 5000, respectively.
A command is executed:

Mysql> SET GLOBAL connection_control_min_connection_delay=3000; //min的不能比max大，所以这个命令会直接报错，除非先修改max，在修改min

What is the result?
A)The minimum connection value is changed to 2000.
B)Only the minimum connection value is increased to 3000.
C)The minimum value increases to 3000 and the maximum value increases to 4000.
D)An error is returned.
Answer:D

该参数为MySQL的连接控制插件安装后才会有的参数
INSTALL PLUGIN CONNECTION_CONTROL_FAILED_LOGIN_ATTEMPTS SONAME 'connection_control.so';
SELECT PLUGIN_NAME,PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME LIKE 'connection%';

mysql> show variables like 'Connection_control_min_connection_delay';
Empty set (0.00 sec)

mysql> show global variables like 'Connection_control_min_connection_delay';
Empty set (0.00 sec)

mysql> INSTALL PLUGIN CONNECTION_CONTROL SONAME 'connection_control.so';
Query OK, 0 rows affected (0.01 sec)

mysql> INSTALL PLUGIN CONNECTION_CONTROL_FAILED_LOGIN_ATTEMPTS SONAME 'connection_control.so';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT PLUGIN_NAME,PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME LIKE 'connection%';
+------------------------------------------+---------------+
| PLUGIN_NAME                              | PLUGIN_STATUS |
+------------------------------------------+---------------+
| CONNECTION_CONTROL                       | ACTIVE        |
| CONNECTION_CONTROL_FAILED_LOGIN_ATTEMPTS | ACTIVE        |
+------------------------------------------+---------------+
2 rows in set (0.00 sec)

mysql> show variables like 'Connection_control_%';
+-------------------------------------------------+------------+
| Variable_name                                   | Value      |
+-------------------------------------------------+------------+
| connection_control_failed_connections_threshold | 3          |
| connection_control_max_connection_delay         | 2147483647 |
| connection_control_min_connection_delay         | 1000       |
+-------------------------------------------------+------------+
3 rows in set (0.01 sec)
connection_control_failed_connections_threshold：允许帐户进行的连续失败尝试的次数。默认为 3 ，表示当连接失败 3 次后启用连接控制，0 表示不开启。
connection_control_max_connection_delay：超出阈值的连接失败的最大延迟(以毫秒为单位)，默认 2147483647 毫秒，约 25 天。
connection_control_min_connection_delay：超过阈值的连接失败的最小延迟(以毫秒为单位)，默认 1000 毫秒，即 1 秒。

参考：https://zhuanlan.zhihu.com/p/410245165

Q10.You must export data from a set of tables in the world_x database. Examine this set of tables:
Tables ( country, countryinfo, location)
Which two option will export data into one or more files?
A)mysql> CLONE LOCAL DATA DIRECTORY = '/var/lib/mysql/world_x/country';
mysql> CLONE LOCAL DATA DIRECTORY = '/var/lib/mysql/world_x/countryinfo';
mysql> CLONE LOCAL DATA DIRECTORY = '/var/lib/mysql/world_x/location';
CLONE是复制其他数据库到本地的，不满足到处数据到一个或者多个文件的条件

B)mysql>SELECT * INTO OUTFILE '/output/contry.txt' FROM world_x.country;
mysql>SELECT * INTO OUTFILE '/output/contryinfo.txt' FROM world_x.countryinfo;
mysql>SELECT * INTO OUTFILE '/output/location.txt' FROM world_x.location;
select * INTO OUTFILE就是将数据导出到数据库外部文件的

C)shell> mysqlexport world_x country countryinfo location > mydump.sql  没有mysqlexport的这个工具
D)shell> mysql --batch world_x.country world_x.countryinfo world_x.location > mydump.sql 
E)shell> mysqldump world_x country countryinfo location > mydump.sql mysqldump就是可以将数据库数据导出到文件中，符合条件
Answer:BE
Q11.Examine this command and output:
Mysql>SELECT *
 FROM performance_schema.table_10_waits_summary_by_table
 WHERE COUNT_STAAR >0\G

performance_schema.table_10_waits_summary_by_table表中可以查询某个表读写的总次数，以及读，写的次数，最小/最大/平均等待时间，FETCH可以简单理解为读取的次数，等待时间等

********************************2.row **************************************
 OBJECT_TYPE:TABLE
OBJECT_SCHEMA:test
OBJECT_NAME:demo_test
CONUNT_STAR:61567093
SUM_TIMER_WAIT:59009007572922
MIN_TIMER_WAIT:395922
AVG_TIMER_WAIT:958095
MAX_TIMER_WAIT:558852005358
COUNT_READ:38665056
SUM_TIMER_READ:20598719962188
MIN_TIMER_READ:395922
AVG_TIMER_READ:532728
MAX_TIMER_READ:558852005358
COUNT_WRITE:22902028
SUM_TIMER_WRITE:38410287610743
MIN_TIMER_WRITE:1130688
AVG_TIMER_WRITE:1677006
MAX_TIMER_WRITE:17205682920
 COUNT_FETCH:38665056
SUM_TIMER_FETCH:20598719962188
MIN_TIMER_FETCH:395922
AVG_TIMER_FETCH:532728
MAX_TIMER_FETCH:558852005358
.....
COUNT_DELETE:22902028
SUM_TIMER_DELETE:38410287610743
MIN_TIMER_DELETE:1130688
AVG_TIMER_DELETE:1677006
MAX_TIMER_DELETE:17205682920
Which two are true?
A)The longest I/O wait was for writes.
B)I/O distribution is approximately 50/50 read/write.
C)22902028 rows were deleted.
D)Average read times are approximately three times faster than writes.
E)The I/O average time is 532728.
Answer:CD

Q12.A developer accidentally dropped the InnoDB table Customers from the Company database. There is a datadir
copy from two days ago in the dbbackup directory.
Which set of steps would restore only the missing table?
A)Stop the MySQL Server process, and execute:
mysqlbackup --datadir=/var/lib/mysql --backup-dir=/dbbackup
--include-tables='Company\.Customers' copy-back
Start the mysqld process.
B)Stop the MySQL Server process and restart it with the command: mysqld --basedir=/usr/local/mysql --
datadir=/var/lib/mysql
Run mysqldump on this table and restore the dump file.
C)Stop the MySQL Server process and restart it with the command: mysqld --basedir=/usr/local/mysql --
datadir=/dbbackup
停止MySQL服务，并使用/dbbackup路径下的备份文件进行恢复
Run mysqldump on this table and restore the dump file.
D)Stop the MySQL Server process, copy the Customers.ibd file from the dbbackup directory, and start the mysqld
process.
Answer:C

Q13.There has been an accidental deletion of data in one of your MySQL databases.
You determine that all entries in the binary log file after position 1797 must be replayed. Examine this partial
command:
mysqlbinlog binlog.000008 --start-position=1798
Which operation will complete the command?
A)--write-to-remote-server must be added to the command line to update the database tables.
B)It can be piped into the MySQL Server via the command-line client.使用该命令通过命令行客户端发送到MySQL服务中
C)You must use --stop-position=1797 to avoid the DELETE statement that caused the initial problem.
D)No changes required. It automatically updates the MySQL Server with the data.
Answer:B

Q14.Table t is an InnoDB table.
Examine these statements and output:
Selet count(1) from t;
+------------+
| count(1) |
+------------+
| 72 |
+------------+
Mysql show indexes from t\G
***************************1.row***************************
 Table: t
 Non_unique:0
Key_name:PRIMARY
Seq_in_index: 1
Column_name: a
Collation:A
Cardinality: 72
Sub_part:NULL
Packed:NULL
Null:
Index_type:STREE
Comment:
Index_comment:
Visible:YES
Expression:NULL
***************************2.row***************************
 Table: t
 Non_unique:1
Key_name:b_idx
Seq_in_index: 1
Column_name: b
Collation:A
Cardinality: 1
Sub_part:NULL
Packed:NULL
Null:YES
Index_type:BTREE
Comment:
Index_comment:
Visible:NO
Expression:NULL
2 row in set (0.00 sec)
可以看到t表有72条数据，主键为a，普通索引为b_idx，Non_unique=0则是唯一索引，Non_unique=1则不是唯一索引。主键的Cardinality则表示索引中唯一值的估计数量，该值是基于统计信息的近似值，可用于评估索引的选择性，选择性高的索引通常性能更好
Which two are true?
A)ANALYZE TABLE t would update index statistics uniquely for the PRIMARY index. analyze是重新收集统计信息，更新索引和表行数的统计信息，不一定只是主键索引
B)Table t has two viable indexes to be used for queries.
t表有两个可用的查询索引，但是visible表示该索引是否对查询优化器可见。由于b字段的索引b_idx的visible为NO，所以，该答案为错
C)SELECT b from t would perform a table scan.
D)Index b_idx has a low number of unique values.
E)SELECT a FROM t would perform a table scan.
Answer:CD

Q15.You are using the InnoDB engine and the innodb_file_per_table option is set. You delete a significant number
of rows of a large table named FACTORY.INVENTORY.
Which command will reorganize the physical storage of table data and associated index data for the INVENTORY
table, in order to reduce storage space and improve I/O efficiency?
A)CHECK TABLE FACTORY.INVENTORY
B)ANALYZE TABLE FACTORY.INVENTORY
C)OPTIMIZE TABLE FACTORY.INVENTORY optimize就可以重新组织数据页的分布，整理碎片，提升IO效率
D)mysqlcheck -u root -p FACTORY.INVENTORY
E)mysqldump -u root -p FACTORY INVENTORY
Answer:C

Q16.The data in this instance transient;no backup or replication will be required.It is currently under performing.
 The database size is static and including indexes is 19G
 Total system memory is 32G
After profiling the system,you highlight these MySQL status and global variables:
Com_rollback |85408355 | 当前实例回滚了85408355次，也是显示的
Com_commit |1234342 | 当前实例提交了1234342次，这个是显示提交，就是明显的执行commit才会统计，隐式的不会统计
Innodb_buffer_pool_pages_free |163840 | innodb buffer pool剩余的页数目。单位是page。
[mysqld]
Buffer_pool_size=20G
Innodb_flush_log_at_trx_commit=2 每次提交写到logfile，不会每次flush到磁盘，这样会降低IO
Disable-log-bin 禁用binlog
The OS metrics indicate that disk is a bottleneck.//操作系统指标显示磁盘是瓶颈
Other variables retain their default values.
Which two changes will provide the most benefit to the instance?

A)Max_connections=10000 连接数对性能不一定有什么影响，可能还会产生负面影响
B Innodb_log_file_size=1G //Innodb_log_file_size参数用于指定 InnoDB 重做日志文件（redo log files）的大小,当 innodb_log_file_size 增大后，日志文件可以容纳更多的日志数据。这意味着在两次日志文件刷盘操作之间，可以累积更多的日志写入操作，从而减少了日志写入磁盘的频率。
C)Sync_binlog=0
D)Innodb_doublewrite=0 //禁用doublerwrite，可以减少一层写入，减少IO，这个有益于优化，具体详细信息可以参考：https://baijiahao.baidu.com/s?id=1672366579747426442&wfr=spider&for=pc
E)Buffer_pool_size=24G //数据只有19G,增加buffer_pool没什么意义
F)Innodb_flush_log_at_trx_commit=1  //每次提交刷新到磁盘，增大IO
Answer:DE
正确的应该是BD，E是错误的

mysql> show global status like 'Com_rollback';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Com_rollback  | 10    |
+---------------+-------+
1 row in set (0.00 sec)
com_rollback：返回当前实例回滚操作执行次数
mysql>
mysql> show global status like 'Com_commit';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Com_commit    | 96    |
+---------------+-------+
1 row in set (0.00 sec)

Com_commit：返回当前实例回滚操作执行次数

innodb_flush_log_at_trx_commit:
如果innodb_flush_log_at_trx_commit设置为0：log buffer将每秒一次地写入log file中，并且log file的flush(刷到磁盘)操作同时进行.该模式下，在事务提交的时候，不会主动触发写入磁盘的操作;
如果innodb_flush_log_at_trx_commit设置为1：每次事务提交时MySQL都会把log buffer的数据写入log file，并且flush(刷到磁盘)中去;
如果innodb_flush_log_at_trx_commit设置为2：每次事务提交时MySQL都会把log buffer的数据写入log file，但是flush(刷到磁盘)操作并不会同时进行。该模式下,MySQL会每秒执行一次 flush(刷到磁盘)操作。

sync_binlog:
当sync_binlog设置为1时，MySQL会在每次提交事务时将binlog缓存中的数据同步到磁盘上。这样可以保证即使发生崩溃，所有已提交的事物也会被记录到binlog中。然而，这样会增加磁盘I/O的负担，可能会对性能产生影响。

如果设置为0（默认值），MySQL将不会在每次事务提交时都进行同步，这样可以提高性能，但是如果发生崩溃，最近的事务可能会丢失。
 

Q17.You are having performance issues with MySQL instances.
Those servers are monitored with MySQL Enterprise Monitor.
Using Query Analyzer, where do you begin to look for problem queries?
A)Look for queries with big prolonged spikes in row activity/access graph in the times series graph.
B)Sort the "Exec" column and check for SQL queries with high Query Response Time index (QRTi) values.
C)Look for queries with low total latency times in the Latency section in the time series graph.
D)Sort the "Exec" column and check for SQL queries with low Query Response Time index (QRTi) values.
Answer:D

A) 在时间序列图中查找行活动/访问图中具有大而持续峰值的查询。
B) 对“Exec”列进行排序并检查具有高查询响应时间指数（QRTi）值的 SQL 查询。
C) 在时间序列图的延迟部分中查找具有低总延迟时间的查询。
D) 对“Exec”列进行排序并检查具有低查询响应时间指数（QRTi）值的 SQL 查询。

例如，如果有 100 次查询执行，其中 60 次在 100ms 内完成（最优），30 次在 100ms 到 400ms 之间完成（可接受），剩下的 10 次超过 400ms（不可接受），则 QRTi 分数为：((60+(30/2)+10*0)/100)=0.75,
从上面可以看到，该值越大，说明可接受，可最优查询占比比较大，如果该值比较小，那么不可接受的慢SQL可能比较多
所以QRTi越小，查询越慢

Q18.Examine the full path name of the backup image from MySQL Enterprise Backup with the --compress option:
/backup/full/mybackup/myimage.img
mysqlbackup.cnf contains this data:
[mysqlbackup]
backup-dir=/backup/full/myrestore
backup-image=/backup/full/mybackup/myimage.img uncompress
You must perform a database restore to a new machine.
which command can provision the new database in datadir as /data/MEB?
A)mysqlbackup --defaults-file=mysqlbackup.cnf --datadir=/data/MEB restore-and-apply-log
B)mysqlbackup --defaults-file=mysqlbackup.cnf --datadir=/data/MEB image-to-dir-and-apply-log
C)mysqlbackup --defaults-file=mysqlbackup.cnf --datadir=/data/MEB apply-log-and-copy-back
D)mysqlbackup --defaults-file=mysqlbackup.cnf --datadir=/data/MEB copy-back-and-apply-log
E)mysqlbackup --defaults-file=mysqlbackup.cnf --datadir=/data/MEB image-to-dir
Answer:D

以下参数是在deepseek中搜索的参数含义，仅供参考

restore-and-apply-log
将备份集恢复到原始位置或指定位置，并应用重做日志文件以恢复数据至最新状态。
目的：用于从备份中恢复数据并确保数据一致性。
适用场景：当需要将备份数据恢复到服务器的原始数据目录时使用。

image-to-dir-and-apply-log
将备份镜像文件恢复到指定目录，并应用重做日志文件。
目的：用于从备份镜像文件中恢复数据到指定目录并确保数据一致性。
适用场景：当需要将备份数据恢复到一个非原始位置进行测试或迁移时使用

apply-log-and-copy-back
应用重做日志文件后，将恢复的数据从备份目录复制回原始数据目录。
目的：用于在应用日志后将数据复制回原始位置。
适用场景：当备份数据被恢复到一个临时目录并经过日志应用后，需要将数据复制回原始数据目录时使用。

copy-back-and-apply-log
先将恢复的数据从备份目录复制回原始数据目录，然后应用重做日志文件。
目的：用于将备份数据复制回原始位置并确保数据一致性。
适用场景：当需要将备份数据直接复制回原始位置并进行日志应用时使用

image-to-dir
将备份镜像文件恢复到指定目录，不应用重做日志文件。
目的：仅将备份镜像文件中的数据恢复到指定目录，不进行日志应用。
适用场景：当需要将备份数据恢复到一个指定目录进行进一步处理或检查时使用。

这些参数用于不同的备份恢复场景，具体使用哪个参数取决于你的恢复需求和目标位置。
restore-and-apply-log：恢复到原始位置并应用日志。
image-to-dir-and-apply-log：从镜像文件恢复到指定目录并应用日志。
apply-log-and-copy-back：先应用日志再复制回原始位置。
copy-back-and-apply-log：先复制回原始位置再应用日志。
image-to-dir：仅从镜像文件恢复到指定目录，不应用日志。

Q19.All mysql server instances belonging to innodb cluster have SSL configured and enabled. You must configure
innodb cluster to use SSL for group communication.
Which two statements are ture?
A)Configuring SSL group communication also configures SSL distributed recovery.
B)SSL group communication requires the use of an additional set of parameters group_replication_recovery_*.
C)If only some innoDB cluster members are enabled for SSL group communication, and
--ssl-mode=PREFERED, communication will fail back to unencrypted connection.
D)An existing innoDB cluster must be dissolved and created form scratch to enable SSL for group communication.
E)SSL group communication can be enabled for an existing cluster,one instance at time,
by setting group_replication_ssl_mode.
F)SSL group communication must be enable at cluster creation time
by pecifying createCluster{{membersslmode:’REQUIRED’}}
Answer:DF

在mysqlshell中有这样的话：
The SSL mode of a cluster can only be set at the time of creation.
但在mysql的官方文档中并没有，因为8.0.27后的版本增加了用mysql自身通讯加密方式，因此并不需要重新创建集群，这里的答案是按旧的文档编写的。
这段话引用自原文链接：https://blog.csdn.net/weixin_43424368/article/details/126382803
 

Q20.Which two are true about differences between logical and physical upgrades of MySQL databases?
A)Post-upgrade table storage requirements after physical upgrades are usually smaller than that after logical
upgrades.
升级后物理存储跟升级前差不多，但是逻辑升级会减少了碎片等，所以逻辑存储会在升级后要求的磁盘空间少
B)Physical upgrades leave data in place, whereas logical upgrades require data to be restored from mysqldumptype backups taken before the upgrades.
物理升级需要将数据保留到原来的位置，逻辑升级需要mysqldump备份，然后进行恢复
C)Physical upgrades are much faster because they do not require restarting the mysqld process.
物理升级比较快因为他们不需要重启MySQL进程，错误的
D)Physical upgrades are performed for current instances on bare metal deployments, whereas logical upgrades are
used for virtual machines or containerized instances.
在物理机上对当前实例进行物理升级，逻辑升级是用于虚拟机或者容器化的实例，这个就是错误的
E)Logical upgrades are much faster because they do not require starting the mysqld process.
逻辑升级更快，因为他们不需要重启MySQL进程
F)Post-upgrade table storage requirements after logical upgrades are usually smaller than that after physical
upgrades.
升级后逻辑升级要求的磁盘空间比物理升级小，所以正确

Answer:BF