问题一：【Hive】explain command throw ClassCastException in 2.3.4

参考：https://issues.apache.org/jira/browse/HIVE-21489

---

（一）问题描述：

     Hive-2.3.4 执行  explain select * from src in hive-2.3.4

    报错： ClassCastException: org.apache.hadoop.hive.ql.parse.ExplainSemanticAnalyzer cannot be cast to org.apache.hadoop.hive.ql.parse.SemanticAnalyzer

（二）解决方法

1. 找到Hive-2.3.4 源码；
2. 修改类：   /ql/src/java/org/apache/hadoop/hive/ql/Driver.java    

diff --git a/ql/src/java/org/apache/hadoop/hive/ql/Driver.java b/ql/src/java/org/apache/hadoop/hive/ql/Driver.java
index cac14a6..70a8028 100644
--- a/ql/src/java/org/apache/hadoop/hive/ql/Driver.java
+++ b/ql/src/java/org/apache/hadoop/hive/ql/Driver.java
@@ -114,6 +114,7 @@
 import org.apache.hadoop.hive.ql.parse.BaseSemanticAnalyzer;
 import org.apache.hadoop.hive.ql.parse.ColumnAccessInfo;
 import org.apache.hadoop.hive.ql.parse.ExplainConfiguration.AnalyzeState;
+import org.apache.hadoop.hive.ql.parse.ExplainSemanticAnalyzer;
 import org.apache.hadoop.hive.ql.parse.HiveSemanticAnalyzerHookContext;
 import org.apache.hadoop.hive.ql.parse.HiveSemanticAnalyzerHookContextImpl;
 import org.apache.hadoop.hive.ql.parse.ImportSemanticAnalyzer;
@@ -1292,10 +1293,14 @@ private static void getTablePartitionUsedColumns(HiveOperation op, BaseSemanticA
     // (par2Cols) or
     // table to columns mapping (tab2Cols)
     if (op.equals(HiveOperation.CREATETABLE_AS_SELECT) || op.equals(HiveOperation.QUERY)) {
-      SemanticAnalyzer querySem = (SemanticAnalyzer) sem;
-      ParseContext parseCtx = querySem.getParseContext();
+      ParseContext parseCtx;
+      if (sem instanceof ExplainSemanticAnalyzer) {
+        parseCtx = ((ExplainSemanticAnalyzer)sem).getParseContext();
+      } else {
+        parseCtx = ((SemanticAnalyzer)sem).getParseContext();
+      }
 
-      for (Map.Entry<String, TableScanOperator> topOpMap : querySem.getParseContext().getTopOps()
+      for (Map.Entry<String, TableScanOperator> topOpMap : parseCtx.getTopOps()
           .entrySet()) {
         TableScanOperator tableScanOp = topOpMap.getValue();
         if (!tableScanOp.isInsideView()) {

         修改类 ：/ql/src/java/org/apache/hadoop/hive/ql/parse/ExplainSemanticAnalyzer.java

diff --git a/ql/src/java/org/apache/hadoop/hive/ql/parse/ExplainSemanticAnalyzer.java b/ql/src/java/org/apache/hadoop/hive/ql/parse/ExplainSemanticAnalyzer.java
index 6d7af38..73ba8e3 100644
--- a/ql/src/java/org/apache/hadoop/hive/ql/parse/ExplainSemanticAnalyzer.java
+++ b/ql/src/java/org/apache/hadoop/hive/ql/parse/ExplainSemanticAnalyzer.java
@@ -56,6 +56,7 @@
 public class ExplainSemanticAnalyzer extends BaseSemanticAnalyzer {
   List<FieldSchema> fieldList;
   ExplainConfiguration config;
+  ParseContext pCtx = null;
 
   public ExplainSemanticAnalyzer(QueryState queryState) throws SemanticException {
     super(queryState);
@@ -189,7 +190,6 @@ public void analyzeInternal(ASTNode ast) throws SemanticException {
       fetchTask.getWork().initializeForFetch(ctx.getOpContext());
     }
 
-    ParseContext pCtx = null;
     if (sem instanceof SemanticAnalyzer) {
       pCtx = ((SemanticAnalyzer)sem).getParseContext();
     }
@@ -285,4 +285,7 @@ public boolean skipAuthorization() {
     return task instanceof ExplainTask && ((ExplainTask)task).getWork().isAuthorize();
   }
 
+  public ParseContext getParseContext() {
+    return pCtx;
+  }
 }

         3. 编译生成class文件，替换hive-exec-2.3.4.jar

         4. 执行以下命令（如果配置有，则不需要）

set hive.security.authorization.enabled=true;
set hive.execution.engine=mr;
set hive.security.authorization.manager=org.apache.hadoop.hive.ql.security.authorization.DefaultHiveAuthorizationProvider;