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https://issues.apache.org/jira/browse/PHOENIX-2797?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15212264#comment-15212264
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Lars Hofhansl commented on PHOENIX-2797:
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Oops. Should have done some checking first. Just wanted to capture it before I
forget about it.
> Ideas to speed up MIN/MAX/DISTINCT for prefixes of the PK
> ---------------------------------------------------------
>
> Key: PHOENIX-2797
> URL: https://issues.apache.org/jira/browse/PHOENIX-2797
> Project: Phoenix
> Issue Type: Improvement
> Reporter: Lars Hofhansl
> Priority: Minor
>
> All of MIN, MAX, and DISTINCT always perform a full scan, even when they are
> on a prefix of a compound key.
> For MIN and MAX one only needs to find the first and last row (resp) and
> we'll have our answer. This works for the full key or a prefix of the key.
> This should work find with or without a WHERE clause, as long as we can
> identify the first and last row.
> For DISTINCT we could do a skip scan to the next prefix (only helps with a
> true prefix of a compound key).
> Say the key is (K1, K2), and say further that we're doing DISTINCT(K1). We
> can skip to the next value of K1 once we found a value. This should have a
> dramatic impact when the cardinality of K2 is high.
> With a WHERE clause that might itself be causing a SKIP SCAN, this might be
> quite tricky. Would need to think about it.
> Both of these statements hold equally when querying against an index.
> Anyway... Just filing this as an idea for now.
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