[jira] [Commented] (PHOENIX-6458) Using global indexes for queries with uncovered columns

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-6458?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17483415#comment-17483415 ] 

ASF GitHub Bot commented on PHOENIX-6458:
-----------------------------------------

kadirozde commented on pull request #1256:
URL: https://github.com/apache/phoenix/pull/1256#issuecomment-1023603041


   > @kadirozde @lhofhansl FYI.
   > 
   > 1.You said "Phoenix client does not use a global index for the queries with the columns that are not covered by the global index" is not right , In QueryOptimizer.addPlan, for the sql with the columns that are not covered by the global index, if user specify a Index Hint and there exists where clause, the sql would be rewritten as "SELECT /*+ NO_INDEX _/ K,V1,V2 FROM T WHERE ("K" IN ((SELECT /_+ INDEX(T IDX) */ ":K" FROM "IDX" WHERE "0:V1" = 'bar')) AND V2 = 'foo') " (k is pk of T , v1 is in IDX and v2 is not), you may consider compatibility with exising code.
   > 
   > 2.Whether or not scaning the gobal index and retrieving the corresponding rows from the data table is better than just scaning the data table is a complex problem, because there are many factors we need to consider such as Network cost, random disk access cost , data distribution , column selective etc. You said "It is expected that such performance improvement will happen when the index row key prefix length is greater than the data row key prefix length for a given query" is extremely insufficient. Lack of a CBO framework in Phoenix, seems that it is sensible to be conservative, I think it is better to left whether or not select this strategy to user by user specifying the Index Hint just as the existing code.
   
   @comnetwork @lhofhansl, I have updated the PR such that the uncovered global indexes will be used only when the index hint is provided as @comnetwork suggested.


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> Using global indexes for queries with uncovered columns
> -------------------------------------------------------
>
>                 Key: PHOENIX-6458
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-6458
>             Project: Phoenix
>          Issue Type: Improvement
>    Affects Versions: 5.1.0
>            Reporter: Kadir Ozdemir
>            Priority: Major
>         Attachments: PHOENIX-6458.master.001.patch
>
>
> Phoenix client does not use a global index for the queries with the columns that are not covered by the global index. However, there are many cases where using the global index to map secondary keys to primary keys and then retrieving the corresponding rows from the data table results in faster queries. It is expected that such performance improvement will happen when the index row key prefix length is greater than the data row key prefix length for a given query. 



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