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https://issues.apache.org/jira/browse/PHOENIX-258?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15311543#comment-15311543
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Lars Hofhansl commented on PHOENIX-258:
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bq. I think what we need is an int[] indexed by the slot position to get the
correct padding to use because the padding necessary depends on the slot
position.
The trick here for reverse case is to seek to the beginning of the first row
with a specific row key. I realized that one can simply seek to the current
rowkey prefix. That will place the "cursor" right before the first occurrence
of this rowkey, which in the reverse case is exactly what we want. No padding
or meddling with the key at all!
> 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-v13.txt, 258-v14.txt, 258-v15.txt, 258-v16.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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