记录下hive数据库启动之后，show databases;报错如下：

hive (default)> show functions;
FAILED: SemanticException org.apache.hadoop.hive.ql.metadata.HiveException: java.lang.RuntimeException: Unable to instantiate org.apache.hadoop.hive.ql.metadata.SessionHiveMetaStoreClient

hadoop集群和hive数据库之前我已经配置好的，启动啥的也是好的

原因：

我在hdfs的web管理网页上讲hive的文件数据清理一空，导致集群中的hive数据库中的数据丢失，然而mysql的存储的元数据又存在，故而在输入查询命令的时候会出现报错

解决办法：

• 1.关闭hive和mysql数据库，在这只是退出来，在hive-site.xml文件末尾添加

<property>
    <name>datanucleus.schema.autoCreateAll</name>
    <value>true</value>
  </property>

• 2.在mysql数据库中删除数据库hivemetadata 数据库，这是存储hive数据库中的所有元数据的，切记生产误用

drop database hivemetadata;

• 3.在集群中所有装有hive的虚拟机中的hive根目录下bin目录下执行如下代码

hive --service metastore &

静静看日志，待出现

[root@linux123 bin]# hive --service metastore &
[1] 8523
[root@linux123 bin]# 2021-11-13 10:42:12: Starting Hive Metastore Server
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/opt/lagou/servers/hive-2.3.7/lib/log4j-slf4j-impl-2.6.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/opt/lagou/servers/hadoop-2.9.2/share/hadoop/common/lib/slf4j-log4j12-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.apache.logging.slf4j.Log4jLoggerFactory]
^C
[root@linux123 bin]# hive
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/opt/lagou/servers/hive-2.3.7/lib/log4j-slf4j-impl-2.6.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/opt/lagou/servers/hadoop-2.9.2/share/hadoop/common/lib/slf4j-log4j12-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.apache.logging.slf4j.Log4jLoggerFactory]

Logging initialized using configuration in jar:file:/opt/lagou/servers/hive-2.3.7/lib/hive-common-2.3.7.jar!/hive-log4j2.properties Async: true
Hive-on-MR is deprecated in Hive 2 and may not be available in the future versions. Consider using a different execution engine (i.e. spark, tez) or using Hive 1.X releases.
hive (default)> show functions;
OK
tab_name
!
!=

说明metastore服务已开启，然后Ctrl+C，再hive,进去