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https://issues.apache.org/jira/browse/PHOENIX-6998?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stephen Yuan Jiang reassigned PHOENIX-6998:
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Assignee: Jing Yu
> Perf regression with server merge query plan for hinted uncovered indexes
> -------------------------------------------------------------------------
>
> Key: PHOENIX-6998
> URL: https://issues.apache.org/jira/browse/PHOENIX-6998
> Project: Phoenix
> Issue Type: Bug
> Components: core
> Reporter: Istvan Toth
> Assignee: Jing Yu
> Priority: Minor
>
> Server merge indexes can be a huge performance win, especially for limit /
> TopN queries that can be resolved on the index table, and which the
> skip-scan-join plan does not push down.
> However, for a large resultset, and poor index selectivity the new server
> merge query plan is still significantly slower than the old skip-scan-join
> plan.
> In one case I had these results:
> unindexed query: 52s
> hinted skip-scan-join query: 90s
> hinted server merge query: 300s
> This was a manufactured worst case dataset, but we can still see that new
> plan can perform significantly worse than the old one.
> As we ultimately read the same cells from both tables, I can only conlcude
> that even the new batched server merge performs worse than getting the rows
> from the client for large resultsets.
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