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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-258) Use skip scan when SELECT DISTINCT on leading row key column(s)
Date Wed, 01 Jun 2016 05:42:12 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-258?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15309316#comment-15309316
] 

Lars Hofhansl commented on PHOENIX-258:
---------------------------------------

Turns out there's a problem for fixed length fields when scanning backwards too:
Say we have rows 1,2,3. Scanning backwards we'll see 3 first. Then we'll seek to 2. That is
right before 2 (not after), so the next key seen would be 1 (not 2).
I think in that case I simply want to 0-pad the seek key. So I would seek to beginning of
a row 2\x00.

> Use skip scan when SELECT DISTINCT on leading row key column(s)
> ---------------------------------------------------------------
>
>                 Key: PHOENIX-258
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-258
>             Project: Phoenix
>          Issue Type: Task
>            Reporter: ryang-sfdc
>            Assignee: Lars Hofhansl
>             Fix For: 4.8.0
>
>         Attachments: 258-WIP.txt, 258-v1.txt, 258-v10.txt, 258-v11.txt, 258-v12.txt,
258-v2.txt, 258-v3.txt, 258-v4.txt, 258-v5.txt, 258-v6.txt, 258-v7.txt, 258-v8.txt, 258-v9.txt,
258.txt, DistinctFixedPrefixFilter.java, in-clause.png
>
>
> create table(a varchar(32) not null, date date not null constraint pk primary key(a,date))
> [["PLAN"],["CLIENT PARALLEL 94-WAY FULL SCAN OVER foo"],["    SERVER AGGREGATE INTO ORDERED
DISTINCT ROWS BY [a]"],["CLIENT MERGE SORT"]]             
> We should skip scan.



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