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: hive.mapred.mode

hive-default.xml：

hive.mapred.mode
nonstrict
The mode in which the hive operations are being performed. In strict mode, some risky queries are not allowed to run



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 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。