[jira] [Commented] (HBASE-17375) PrefixTreeArrayReversibleScanner#previousRowInternal doesn't work correctly

["ramkrishna.s.vasudevan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-17375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15778084#comment-15778084 ] 

ramkrishna.s.vasudevan commented on HBASE-17375:
------------------------------------------------

[~baibaichen]
Thanks for the nice analysis. Do you like to give a patch with a test for the above case? 

> PrefixTreeArrayReversibleScanner#previousRowInternal doesn't work correctly
> ---------------------------------------------------------------------------
>
>                 Key: HBASE-17375
>                 URL: https://issues.apache.org/jira/browse/HBASE-17375
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 1.1.7, 0.98.23, 0.98.24
>            Reporter: Chang chen
>         Attachments: row trie example.PNG
>
>
> Recently, we find our hbase compaction thread never end.  Assume we have following cells:
> {quote}
> <A,a> 1
> <A,v> 1
> <Aaeeee,a> 1
> <Aaeeee,v> 1
> <Abc,a> 1
> <Abc,v> 1
> <Abde,a> 1
> <Abde,v> 1
> {quote}
> If we encode above datas into prefix tree block, then it looks like:
> !row trie example.PNG!
> Assume the current row is {color:red}Abc{color} (e.g. the current row node is 4), then the previous row should be *Aaeeee* (e.g. 2). However previousRowInternal return {color:red}A{color}(e.g. 1)
> After investigation, I believe it's the bug of PrefixTreeArrayReversibleScanner#previousRowInternal.
> {code}
>   private boolean previousRowInternal() {
>     //...
>     while (!beforeFirst) {
>       //....
>       // what if currentRowNode is nub?
>       if (currentRowNode.hasOccurrences()) {// escape clause
>         currentRowNode.resetFanIndex();
>         return true;// found some values
>       }
>     }
> {code}
> currentRowNode.hasOccurrences() only test whether it has cell or not. But in the case of  currentRowNode.isNub() is true, previousRowInternal should follow the previous fan instead of return.



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