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From "Viral Bajaria (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9079) FilterList getNextKeyHint skips rows that should be included in the results
Date Tue, 06 Aug 2013 19:15:49 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13731130#comment-13731130
] 

Viral Bajaria commented on HBASE-9079:
--------------------------------------

If we take the largest seekHint, the problem can be explained as follows:

- FilterList with FuzzyRow + ColumnRange with MUST_PASS_ALL.
- FuzzyRow includes the filter and says move on to ColumnRange.
- ColumnRange says first column is not a match and I can give you a better seekHint
- FilterList calls seekHint on both FuzzyRow and ColumnRange. FuzzyRow returns the next row
that we should use while ColumnRange returns the next column from the originally selected
row. If we keep max here then we move on to the next row and do no return the columns from
the row that should have been returned. The test case proves that this is what happened originally
(though I removed the TestFail.patch due to some Hadoop QA issues)

Yes the current changes work even if you change the ordering of filters. The test in the patch
verified that behavior too.

                
> FilterList getNextKeyHint skips rows that should be included in the results
> ---------------------------------------------------------------------------
>
>                 Key: HBASE-9079
>                 URL: https://issues.apache.org/jira/browse/HBASE-9079
>             Project: HBase
>          Issue Type: Bug
>          Components: Filters
>    Affects Versions: 0.94.10
>            Reporter: Viral Bajaria
>             Fix For: 0.98.0, 0.95.2, 0.94.12
>
>         Attachments: HBASE-9079-0.94.patch, HBASE-9079-trunk.patch
>
>
> I hit a weird issue/bug and am able to reproduce the error consistently. The problem
arises when FilterList has two filters where each implements the getNextKeyHint method.
> The way the current implementation works is, StoreScanner will call matcher.getNextKeyHint()
whenever it gets a SEEK_NEXT_USING_HINT. This in turn will call filter.getNextKeyHint() which
at this stage is of type FilterList. The implementation in FilterList iterates through all
the filters and keeps the max KeyValue that it sees. All is fine if you wrap filters in FilterList
in which only one of them implements getNextKeyHint. but if multiple of them implement then
that's where things get weird.
> For example:
> - create two filters: one is FuzzyRowFilter and second is ColumnRangeFilter. Both of
them implement getNextKeyHint
> - wrap them in FilterList with MUST_PASS_ALL
> - FuzzyRowFilter will seek to the correct first row and then pass it to ColumnRangeFilter
which will return the SEEK_NEXT_USING_HINT code.
> - Now in FilterList when getNextKeyHint is called, it calls the one on FuzzyRow first
which basically says what the next row should be. While in reality we want the ColumnRangeFilter
to give the seek hint.
> - The above behavior skips data that should be returned, which I have verified by using
a RowFilter with RegexStringComparator.
> I updated the FilterList to maintain state on which filter returns the SEEK_NEXT_USING_HINT
and in getNextKeyHint, I invoke the method on the saved filter and reset that state. I tested
it with my current queries and it works fine but I need to run the entire test suite to make
sure I have not introduced any regression. In addition to that I need to figure out what should
be the behavior when the opeation is MUST_PASS_ONE, but I doubt it should be any different.
> Is my understanding of it being a bug correct ? Or am I trivializing it and ignoring
something very important ? If it's tough to wrap your head around the explanation, then I
can open a JIRA and upload a patch against 0.94 head.

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