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

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

abstractdog commented on a change in pull request #2693:
URL: https://github.com/apache/hive/pull/2693#discussion_r733352864



##########
File path: ql/src/java/org/apache/hadoop/hive/ql/exec/LimitOperator.java
##########
@@ -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:
       @dengzhhu653: I'm trying to understand how the original implementation led to empty result in MR, and why is the !tez condition helped...this will force the code to hit below codepath in MR, where we throw an exception if runtimeCache is null outside of HS2 or instantiate runtimeCache (in HS2)
   
   without this patch, what happened in case of MR? I guess as the patch forced to hit this condition:
   ```
   runtimeCache == null || !HiveConf.getVar(hconf, HiveConf.ConfVars.HIVE_EXECUTION_ENGINE).equals("tez")
   ```
   even if the runtimeCache is not null, so runtimeCache should not have been null originally...if so, what's the value of the code inside condition
   




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