[GitHub] [hive] dengzhhu653 commented on a change in pull request #2693: HIVE-25582: Empty result when using offset limit with MR

[GitBox <gi...@apache.org>]

dengzhhu653 commented on a change in pull request #2693:
URL: https://github.com/apache/hive/pull/2693#discussion_r733382781



##########
File path: ql/src/java/org/apache/hadoop/hive/ql/exec/LimitOperator.java
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@@ -69,8 +69,8 @@ protected void initializeOp(Configuration hconf) throws HiveException {
     this.runtimeCache = ObjectCacheFactory.getCache(getConfiguration(), queryId, false, true);
 
     // this can happen in HS2 while doing local fetch optimization, where LimitOperator is used
-    if (runtimeCache == null) {
-      if (!HiveConf.isLoadHiveServer2Config()) {
+    if (runtimeCache == null || !HiveConf.getVar(hconf, HiveConf.ConfVars.HIVE_EXECUTION_ENGINE).equals("tez")) {

Review comment:
        when the engine is not tez, [org.apache.hadoop.hive.ql.exec.mr.ObjectCache](https://github.com/apache/hive/blob/1090c93b1a02d480bdee2af2cecf503f8a54efc6/ql/src/java/org/apache/hadoop/hive/ql/exec/ObjectCacheFactory.java#L80-L83) will be the runtime cache, we do not persist any thing in this cache. so every time we [fetch the row counter from the cache](https://github.com/apache/hive/blob/7b3ecf617a6d46f48a3b6f77e0339fd4ad95a420/ql/src/java/org/apache/hadoop/hive/ql/exec/LimitOperator.java#L150-L158), a newly created AtomicInteger will be returned,  the condition `offset <= currentCountForAllTasksInt` https://github.com/apache/hive/blob/7b3ecf617a6d46f48a3b6f77e0339fd4ad95a420/ql/src/java/org/apache/hadoop/hive/ql/exec/LimitOperator.java#L98 will be evaluated to false with offset > 0, making the operator unable to forward any rows to downstream.




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