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https://issues.apache.org/jira/browse/HIVE-7232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14033253#comment-14033253
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Navis commented on HIVE-7232:
-----------------------------
_col10 is null which is "VALUE._col0" of MAP2, which is again "o_orderkey"
{noformat}
Reduce Output Operator
key expressions: o_custkey (type: int)
sort order: +
Map-reduce partition columns: o_custkey (type: int)
Statistics: Num rows: 166666666 Data size: 86571942280 Basic stats: COMPLETE
Column stats: NONE
value expressions: o_orderkey (type: int), o_orderdate (type: string)
{noformat}
Is the table "orders" contains nulls?
> ReduceSink is emitting NULL keys due to failed keyEval
> ------------------------------------------------------
>
> Key: HIVE-7232
> URL: https://issues.apache.org/jira/browse/HIVE-7232
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Affects Versions: 0.14.0
> Reporter: Gopal V
> Assignee: Navis
> Attachments: HIVE-7232-extra-logging.patch, q5.explain.txt, q5.sql
>
>
> After HIVE-4867 has been merged in, some queries have exhibited a very weird
> skew towards NULL keys emitted from the ReduceSinkOperator.
> Added extra logging to print expr.column() in ExprNodeColumnEvaluator & in
> reduce sink.
> {code}
> 2014-06-14 00:37:19,186 INFO [TezChild]
> org.apache.hadoop.hive.ql.exec.ReduceSinkOperator:
> numDistributionKeys = 1 {null --> ExprNodeColumnEvaluator(_col10)}
> key_row={"reducesinkkey0":442}
> {code}
> {code}
> HiveKey firstKey = toHiveKey(cachedKeys[0], tag, null);
> int distKeyLength = firstKey.getDistKeyLength();
> if(distKeyLength <= 1) {
> StringBuffer x1 = new StringBuffer();
> x1.append("numDistributionKeys = "+ numDistributionKeys + "\n");
> for (int i = 0; i < numDistributionKeys; i++) {
> x1.append(cachedKeys[0][i] + " --> " + keyEval[i] + "\n");
> }
> x1.append("key_row="+ SerDeUtils.getJSONString(row,
> keyObjectInspector));
> LOG.info("GOPAL: " + x1.toString());
> }
> {code}
> The query is tpc-h query5, with extra NULL checks just to be sure.
> {code}
> ELECT n_name,
> sum(l_extendedprice * (1 - l_discount)) AS revenue
> FROM customer,
> orders,
> lineitem,
> supplier,
> nation,
> region
> WHERE c_custkey = o_custkey
> AND l_orderkey = o_orderkey
> AND l_suppkey = s_suppkey
> AND c_nationkey = s_nationkey
> AND s_nationkey = n_nationkey
> AND n_regionkey = r_regionkey
> AND r_name = 'ASIA'
> AND o_orderdate >= '1994-01-01'
> AND o_orderdate < '1995-01-01'
> and l_orderkey is not null
> and c_custkey is not null
> and l_suppkey is not null
> and c_nationkey is not null
> and s_nationkey is not null
> and n_regionkey is not null
> GROUP BY n_name
> ORDER BY revenue DESC;
> {code}
> The reducer which has the issue has the following plan
> {code}
> Reducer 3
> Reduce Operator Tree:
> Join Operator
> condition map:
> Inner Join 0 to 1
> condition expressions:
> 0 {KEY.reducesinkkey0} {VALUE._col2}
> 1 {VALUE._col0} {KEY.reducesinkkey0} {VALUE._col3}
> outputColumnNames: _col0, _col3, _col10, _col11, _col14
> Statistics: Num rows: 183333344 Data size: 95229140992 Basic
> stats: COMPLETE Column stats: NONE
> Reduce Output Operator
> key expressions: _col10 (type: int)
> sort order: +
> Map-reduce partition columns: _col10 (type: int)
> Statistics: Num rows: 183333344 Data size: 95229140992
> Basic stats: COMPLETE Column stats: NONE
> value expressions: _col0 (type: int), _col3 (type: int),
> _col11 (type: int), _col14 (type: string)
> {code}
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