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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-4288) Indexes not used when ordering by primary key
Date Fri, 17 Nov 2017 08:12:00 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-4288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16256621#comment-16256621
] 

ASF GitHub Bot commented on PHOENIX-4288:
-----------------------------------------

Github user JamesRTaylor commented on a diff in the pull request:

    https://github.com/apache/phoenix/pull/281#discussion_r151623809
  
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/optimize/QueryOptimizer.java ---
    @@ -91,8 +91,23 @@ public QueryPlan optimize(PhoenixStatement statement, SelectStatement
select, Co
         }
         
         public QueryPlan optimize(QueryPlan dataPlan, PhoenixStatement statement, List<?
extends PDatum> targetColumns, ParallelIteratorFactory parallelIteratorFactory) throws
SQLException {
    -        List<QueryPlan>plans = getApplicablePlans(dataPlan, statement, targetColumns,
parallelIteratorFactory, true);
    -        return plans.get(0);
    +        List<QueryPlan> plans = getApplicablePlans(dataPlan, statement, targetColumns,
parallelIteratorFactory, false);
    +        if (plans.size() == 1) {
    +            return plans.get(0);
    +        }
    +
    +        // Get the best plan based on their costs. Costs will be ZERO if stats are not
    +        // available, thus the first plan will be returned.
    +        Cost minCost = null;
    +        QueryPlan bestPlan = null;
    +        for (QueryPlan plan : plans) {
    +            Cost cost = plan.getCost();
    +            if (minCost == null || cost.compareTo(minCost) < 0) {
    +                minCost = cost;
    +                bestPlan = plan;
    +            }
    +        }
    +        return bestPlan;
    --- End diff --
    
    I agree with @katameru. If you plug in your optimization code to impact the sort order
done by QueryOptimizer.orderPlansBestToWorst() when getApplicablePlans() is called, we'd keep
the behavior that the hints would override the optimizer (whether cost-based is enabled or
not).
    
    I still think we need more tests. We've found that if the tests don't get added with the
initial commit, they unfortunately never get added. 


> Indexes not used when ordering by primary key
> ---------------------------------------------
>
>                 Key: PHOENIX-4288
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-4288
>             Project: Phoenix
>          Issue Type: Sub-task
>            Reporter: Marcin Januszkiewicz
>            Assignee: Maryann Xue
>              Labels: CostBasedOptimization
>
> We have a table
> CREATE TABLE t (
>   rowkey VARCHAR PRIMARY KEY,
>   c1 VARCHAR,
>   c2 VARCHAR
> )
> which we want to query by doing partial matches on c1, and keep the ordering of the source
table:
> SELECT rowkey, c1, c2 FROM t where c1 LIKE 'X0%' ORDER BY rowkey;
> We expect most queries to select a small subset of the table, so we create an index to
speed up searches:
> CREATE LOCAL INDEX t_c1_ix ON t (c1);
> However, this index will not be used since Phoenix will always choose not to resort the
data.
> In our actual use case, adding index hints is not a practical solution.
> See also discussion at:
> https://lists.apache.org/thread.html/26ab58288eb811d2f074c3f89067163d341e5531fb581f3b2486cf43@%3Cuser.phoenix.apache.org%3E



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