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Date: Fri, 15 Dec 2017 08:44:00 +0000 (UTC)
From: "Vladimir Ozerov (JIRA)" <jira@apache.org>
To: issues@ignite.apache.org
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Subject: [jira] [Resolved] (IGNITE-7167) Optimize 'select count(*) from
 Table'
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archived-at: Fri, 15 Dec 2017 08:44:06 -0000


     [ https://issues.apache.org/jira/browse/IGNITE-7167?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vladimir Ozerov resolved IGNITE-7167.
-------------------------------------
    Resolution: Duplicate

We already optimized this, see IGNITE-6702. We cannot get rid of scan in general case. For now we iterate over index entries and count them. This is the best what can be done. 

However, when MVCC is ready, we will have to resort to (almost) original approach - for every entry in the index we would have to check whether it is visible.

> Optimize 'select count(*) from Table'
> -------------------------------------
>
>                 Key: IGNITE-7167
>                 URL: https://issues.apache.org/jira/browse/IGNITE-7167
>             Project: Ignite
>          Issue Type: Improvement
>          Components: sql
>    Affects Versions: 2.3
>            Reporter: Valentin Kulichenko
>
> Currently query like {{select count(*) from Table}} effectively scans the cache and take a lot of time for large datasets. Probably makes sense to optimize it to use {{IgniteCache#size}} directly when possible.


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