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From "ASF GitHub Bot (Jira)" <j...@apache.org>
Subject [jira] [Commented] (KYLIN-4810) TrieDictionary is not correctly build
Date Fri, 13 Nov 2020 01:50:00 GMT

    [ https://issues.apache.org/jira/browse/KYLIN-4810?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17231081#comment-17231081
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ASF GitHub Bot commented on KYLIN-4810:
---------------------------------------

hit-lacus commented on pull request #1477:
URL: https://github.com/apache/kylin/pull/1477#issuecomment-726455006


   @bigxiaochu Could you please help to review this patch ?


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> TrieDictionary is not correctly build
> -------------------------------------
>
>                 Key: KYLIN-4810
>                 URL: https://issues.apache.org/jira/browse/KYLIN-4810
>             Project: Kylin
>          Issue Type: Bug
>          Components: Job Engine
>    Affects Versions: v2.3.2
>            Reporter: ShengJun Zheng
>            Priority: Critical
>             Fix For: Future
>
>
> Hi, recently, I've met a problem in our product environment: Segments failed to merge
because TrieDictionaryForest was disordered
> {code:java}
> java.lang.IllegalStateException: Invalid input data. Unordered data cannot be split into
multi trees
>     at org.apache.kylin.dict.TrieDictionaryForestBuilder.addValue(TrieDictionaryForestBuilder.java:92)
>     at org.apache.kylin.dict.TrieDictionaryForestBuilder.addValue(TrieDictionaryForestBuilder.java:78)
>     at org.apache.kylin.dict.DictionaryGenerator$StringTrieDictForestBuilder.addValue(DictionaryGenerator.java:214)
>     at org.apache.kylin.dict.DictionaryGenerator.buildDictionary(DictionaryGenerator.java:81)
>     at org.apache.kylin.dict.DictionaryGenerator.buildDictionary(DictionaryGenerator.java:65)
>     at org.apache.kylin.dict.DictionaryGenerator.mergeDictionaries(DictionaryGenerator.java:106)
> {code}
> After some analysis, we found out when there is large values in a dict-encoded column,
iterating over a single TrieDictionaryTree will get unordered data.
>  
>  Digging into the source code,  the root cause is as described: 
>  # Kylin will split a TrieTree Node into two parts when a single nodes's value length
is more than 255 bytes
>  # Then, these tow parts of value will be added to build the TrieTree. In fact the splitted
two parts should not be used as new values to add to the TrieTree.
>  # Step 2 will cause the TrieDictionaryTree build more leave nodes,and the extra leaf
nodes will be 'end-value' of dictionary tree;
>  # It has no impact to the correctness of the dict tree itself, except for adding some
additional nodes .
>  # But If you spit a UTF-8 word, you will get unordered data when iterating over the
tree ( Something todo with Java UTF-8  String Serialize/Deserialize implementations. Please
Refer to JDK sun.nio.cs.UTF_8.class)
> How to re-produce ? Run test code :
> {code:java}
> TrieDictionaryForestBuilder builder = new TrieDictionaryForestBuilder(new StringBytesConverter());
> String longUrl = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好~~~";
> builder.addValue(longUrl);
> TrieDictionaryForest<String> dict = builder.build();
> TrieDictionaryForestBuilder mergeBuild = new TrieDictionaryForestBuilder(new StringBytesConverter());
> for (int i = dict.getMinId(); i <= dict.getMaxId(); i++) {
>     String str = dict.getValueFromId(i);
>     System.out.println("add value into merge tree");
>     mergeBuild.addValue(str);
> }
> The log output of this test code is:
> add value into merge tree
> add value into merge tree
> 16:59:36 [main] INFO org.apache.kylin.dict.TrieDictionaryForestBuilder.addValue(TrieDictionaryForestBuilder.java:127)
values not in ascending order, previous 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\xEF\xBF\xBD',
current 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\xE4\xBD\xA0\xE5\xA5\xBD~~~'
> {code}
> We can see from the test code's output:
>  # We only add 1 value but the tire dictionary tree turn out to have 2 end vlaues
>  # Iterating over the TrieDictionary Tree got unordered data
> We address this problem by
>  # classify values which is a whole column value, which is splitted value,
>  # not mark splitted value as end-value of a TrieTree Node.
> I wonder if there is something wrong, thanks.



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