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https://issues.apache.org/jira/browse/PHOENIX-6501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17505073#comment-17505073
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Lars Hofhansl commented on PHOENIX-6501:
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With the latest version of this patch the query finishes, but it still take a
very long time.
Same scenario: 18m rows, count\(*) matching 2m rows. Without index the query
takes about 7s on my system, with a local index it takes 10s, with the global
index and this patch it takes about 4 minutes. A cursory look in the profiler
reveals that most time is spent in ClientScanner.next()...
>From the code it's not immediately clear what the problem is.
> Use batching when joining data table rows with uncovered global index rows
> --------------------------------------------------------------------------
>
> Key: PHOENIX-6501
> URL: https://issues.apache.org/jira/browse/PHOENIX-6501
> Project: Phoenix
> Issue Type: Improvement
> Affects Versions: 5.1.2
> Reporter: Kadir Ozdemir
> Assignee: Lars Hofhansl
> Priority: Major
> Attachments: PHOENIX-6501.master.001.patch
>
>
> PHOENIX-6458 extends the existing uncovered local index support for global
> indexes. The current solution uses HBase get operations to join data table
> rows with uncovered index rows on the server side. Doing a separate RPC call
> for every data table row can be expensive. Instead, we can buffer lots of
> data row keys in memory, use a skip scan filter and even multiple threads to
> issue a separate scan for each data table region in parallel. This will
> reduce the cost of join and also improve the performance.
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