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https://issues.apache.org/jira/browse/PHOENIX-3156?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15410407#comment-15410407
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Lars Hofhansl commented on PHOENIX-3156:
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Unfortunately the patch undoes the optimization. Sigh. :(
> Bug in DistinctPrefixFilter
> ---------------------------
>
> Key: PHOENIX-3156
> URL: https://issues.apache.org/jira/browse/PHOENIX-3156
> Project: Phoenix
> Issue Type: Bug
> Reporter: Lars Hofhansl
> Priority: Blocker
> Fix For: 4.8.0
>
> Attachments: 3156.txt
>
>
> There's a corner case I found where a DISTINCT and GROUP BY query along a
> prefix of a compound row key might return incorrect results.
> The filter relies on seeing the _0 column absolutely last, and not seeing all
> Cells that should be filtered. That break in two scenarios:
> # we have a table with key (key1, key2, key3) and columns (c1 and c2). Now
> construct a WHERE <a clause that always matches c1>, <a clause that filters
> by c2) GROUP BY key1, key2. Now the filter would mis-skip when it sees the
> Cell for c1.
> # we force lower key column names. In that case those would sort after the _0
> column. The DistinctPrefixFilter would see the _0 column first and skip.
> In both case we are effectively changing the order in which the filters are
> applied. The DistinctPrefixFilter is no longer for the row.
> I can fix #1 (by ignoring all Cells other than then _0 one). I do not know
> how to fix case #2.
> I think this is a blocker and we may have to undo the entire DISTINCT and
> GROUP BY prefix optimization.
> [~an...@apache.org], [~giacomotaylor], [~samarthjain].
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