hive strict模式

set hive.mapred.mode=nonstrict;
set hive.mapred.mode=strict;

hive> set hive.mapred.mode;
hive.mapred.mode=nonstrict
hive> set hive.mapred.mode=strict;
hive> select key, value from src order by key,value;
FAILED: Error in semantic analysis: line 1:36 In strict mode, limit must be specified if ORDER BY is present value
hive>


HiveConf：
HIVEMAPREDMODE("hive.mapred.mode", "nonstrict"),

tianzhao@ubuntu:~/hive/trunk/hive-0.6.0/conf$ grep -r "hive.mapred.mode" ../conf/
../conf/hive-default.xml:  <name>hive.mapred.mode</name>

hive-default.xml：
<property>
  <name>hive.mapred.mode</name>
  <value>nonstrict</value>
  <description>The mode in which the hive operations are being performed. In strict mode, some risky queries are not allowed to run</description>
</property>


strict：
出现的地方：
（1）
  private Operator genJoinReduceSinkChild(QB qb, QBJoinTree joinTree,
      Operator child, String srcName, int pos) throws SemanticException {

    // Use only 1 reducer in case of cartesian product
    if (reduceKeys.size() == 0) {
      numReds = 1;

      // Cartesian product is not supported in strict mode
      if (conf.getVar(HiveConf.ConfVars.HIVEMAPREDMODE).equalsIgnoreCase(
          "strict")) {
        throw new SemanticException(ErrorMsg.NO_CARTESIAN_PRODUCT.getMsg());
      }
    }

}

hive> set hive.mapred.mode=strict;
hive> EXPLAIN SELECT subq.key, tab.value FROM src subq JOIN src tab  where subq.key < 200;
FAILED: Error in semantic analysis: In strict mode, cartesian product is not allowed. If you really want to perform the operation, set hive.mapred.mode=nonstrict



（2）
  private Operator genReduceSinkPlan(String dest, QB qb, Operator input,
      int numReducers) throws SemanticException {

    if (sortExprs == null) {
      sortExprs = qb.getParseInfo().getOrderByForClause(dest);
      if (sortExprs != null) {
        assert numReducers == 1;
        // in strict mode, in the presence of order by, limit must be specified
        Integer limit = qb.getParseInfo().getDestLimit(dest);
        if (conf.getVar(HiveConf.ConfVars.HIVEMAPREDMODE).equalsIgnoreCase(
            "strict")
            && limit == null) {
          throw new SemanticException(ErrorMsg.NO_LIMIT_WITH_ORDERBY
              .getMsg(sortExprs));
        }
      }
    }

}

（3）
  public static PrunedPartitionList prune(Table tab, ExprNodeDesc prunerExpr,
      HiveConf conf, String alias,
      Map<String, PrunedPartitionList> prunedPartitionsMap) throws HiveException {
    
          // If the "strict" mode is on, we have to provide partition pruner for
          // each table.
          if ("strict".equalsIgnoreCase(HiveConf.getVar(conf,
              HiveConf.ConfVars.HIVEMAPREDMODE))) {
            if (!hasColumnExpr(prunerExpr)) {
              throw new SemanticException(ErrorMsg.NO_PARTITION_PREDICATE
                  .getMsg("for Alias \"" + alias + "\" Table \""
                  + tab.getTableName() + "\""));
            }
          }

}

strict模式在下面三种情况下有限制：
(1) partition表需要加上分区裁剪
(2) order by 只有一个reduce，需要加上limit
(3) join时，如果只有一个reduce，笛卡尔积不支持。