# Hive SQL常见配置类问题
- Hive SQL执行报错：java.lang.OutOfMemoryError: Java heap space. 解决方案：
  - 对于MapReduce任务，增大下列参数： **set mapreduce.map.memory.mb=8192;**
    **set mapreduce.map.java.opts=-Xmx6554M;**
    **set mapreduce.reduce.memory.mb=8192;**
    **set mapreduce.reduce.java.opts=-Xmx6554M;**
    
  
  - 对于Tez任务，增大下列参数： **set hive.tez.container.size=8192;**
    
   
- Hive SQL对列名as为新列名后，使用原列名编译报错：Invalid table alias or column reference 'xxx'. 解决方案：**set hive.cbo.enable=true;**
  
- Hive SQL子查询编译报错：Unsupported SubQuery Expression 'xxx': Only SubQuery expressions that are top level conjuncts are allowed. 解决方案：**set hive.cbo.enable=true** **;**
  
- Hive SQL子查询编译报错：CalciteSubquerySemanticException \[Error 10249\]: Unsupported SubQuery Expression Currently SubQuery expressions are only allowed as Where and Having Clause predicates. 解决方案：**set hive.cbo.enable=true;**
  
- Hive SQL编译报错：Error running query: java.lang.AssertionError: Cannot add expression of different type to set. 解决方案：**set hive.cbo.enable=false;**
  
- Hive SQL执行报错：java.lang.NullPointerException at org.apache.hadoop.hive.ql.udf.generic.GenericUDAFComputeStats$GenericUDAFNumericStatsEvaluator.init. 解决方案：**set hive.map.aggr=false;**
  
- Hive SQL设置hive.auto.convert.join = true（默认开启）和hive.optimize.skewjoin=true执行报错：ClassCastException org.apache.hadoop.hive.ql.plan.ConditionalWork cannot be cast to org.apache.hadoop.hive.ql.plan.MapredWork. 解决方案：**set hive.optimize.skewjoin=false;**
  
- Hive SQL设置hive.auto.convert.join=true（默认开启）、hive.optimize.skewjoin=true和hive.exec.parallel=true执行报错：java.io.FileNotFoundException: File does not exist:xxx/reduce.xml. 解决方案：
  - 方法一：切换执行引擎为Tez，详情请参考[切换Hive执行引擎](https://support.huaweicloud.com/cmpntguide-lts-mrs/mrs_01_1750.html)。
  
  - 方法二：**set hive.exec.parallel=false;**
  
  - 方法三：**set hive.auto.convert.join=false;**
   
- Hive on Tez执行Bucket表Join报错：NullPointerException at org.apache.hadoop.hive.ql.exec.CommonMergeJoinOperator.mergeJoinComputeKeys 解决方案：**set tez.am.container.reuse.enabled=false;**