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From "Taras Ledkov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IGNITE-11756) SQL: implement a table row count statistics for the local queries
Date Mon, 13 May 2019 09:44:00 GMT

    [ https://issues.apache.org/jira/browse/IGNITE-11756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16838415#comment-16838415
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Taras Ledkov commented on IGNITE-11756:
---------------------------------------

[~rkondakov]. my comments:
1. Is the member {{GridH2Table#size}} contains correct size value for persistence tables after
restart a node?
2. Why the {{GridH2Table#getRowCountApproximation}} uses the {{GridH2Table#size}} instead
of {{GridH2Table.TableStatistics#getRowCountStatistics}}? This method may be used on the optimization
step too.


> SQL: implement a table row count statistics for the local queries
> -----------------------------------------------------------------
>
>                 Key: IGNITE-11756
>                 URL: https://issues.apache.org/jira/browse/IGNITE-11756
>             Project: Ignite
>          Issue Type: Improvement
>          Components: sql
>            Reporter: Roman Kondakov
>            Assignee: Roman Kondakov
>            Priority: Major
>          Time Spent: 20m
>  Remaining Estimate: 0h
>
> Row count statistics should help the H2 optimizer to select the better query execution
plan. Currently the row count supplied to H2 engine is hardcoded value == 10000 (see {{org.h2.index.Index#getRowCountApproximation}}). 
As a first step we can provide an actual table size in the case of local query. To prevent
counting size on each invocation we can cache row count value and invalidate it in some cases:
>  * Rebalancing
>  * Multiple updates (after the initial loading)
>  * On timeout (i.e. 1 minute)



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