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Posted to issues@hawq.apache.org by huor <gi...@git.apache.org> on 2016/06/20 03:11:40 UTC

[GitHub] incubator-hawq pull request #731: HAWQ-830. Fix wrong result in CTE query du...

GitHub user huor opened a pull request:

    https://github.com/apache/incubator-hawq/pull/731

    HAWQ-830. Fix wrong result in CTE query due to CTE is treated as init plan by planner and evaluated multiple times

    

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/huor/incubator-hawq huor_cte

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/incubator-hawq/pull/731.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #731
    
----
commit 93c9f3b1d2d52f19086da006f5e02813527cfb5c
Author: Ruilong Huo <rh...@pivotal.io>
Date:   2016-06-20T03:12:32Z

    HAWQ-830. Fix wrong result in CTE query due to CTE is treated as init plan by planner and evaluated multiple times

----


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[GitHub] incubator-hawq issue #731: HAWQ-830. Fix wrong result in CTE query due to CT...

Posted by huor <gi...@git.apache.org>.

Github user huor commented on the issue:

    https://github.com/apache/incubator-hawq/pull/731
  
    @vraghavan78, yes, you are correct.
    
    gp_cte_sharing was introduced to workaround deadlock in shared scan in some CTE queries. For example, https://issues.apache.org/jira/browse/HAWQ-852 is a hang issue when gp_cte_sharing is on.
    
    However, if we disable gp_cte_sharing (especially by default), we get wrong result when running some other CTE queries. One of the common root cause is that: with gp_cte_sharing off, some of the CTE expressions are evaluated multiple times in one single query; if the CTE expression itself is somehow "volatile", it is obviously that wrong result (at least inconsistent result) will be generated.
    For example, https://issues.apache.org/jira/browse/HAWQ-830, https://issues.apache.org/jira/browse/HAWQ-852 are two issues that generate wrong results with CTE query.
    
    My recommendation is: we need to enable gp_cte_sharing by default (actually this GUC should be removed ideally), and then fix the hang issue in shared scan. Your thoughts?


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[GitHub] incubator-hawq issue #731: HAWQ-830. Fix wrong result in CTE query due to CT...

Posted by edespino <gi...@git.apache.org>.

Github user edespino commented on the issue:

    https://github.com/apache/incubator-hawq/pull/731
  
    @huor - Any update on this PR?  There hasn't been any progress on it in months. This is the same for the corresponding Jira HAWQ-830


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[GitHub] incubator-hawq issue #731: HAWQ-830. Fix wrong result in CTE query due to CT...

Posted by huor <gi...@git.apache.org>.

Github user huor commented on the issue:

    https://github.com/apache/incubator-hawq/pull/731
  
    @edespino, it is better to merge this fix along with extra fix for wrong result and hang in CTE query. Given there is a lot of effort to fix the wrong result and hang in CTE, I think we can close this pr without merge it for now. We can do that when they are fixed.


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[GitHub] incubator-hawq issue #731: HAWQ-830. Fix wrong result in CTE query due to CT...

Posted by zhangh43 <gi...@git.apache.org>.

Github user zhangh43 commented on the issue:

    https://github.com/apache/incubator-hawq/pull/731
  
    GUC gp_cte_sharing cannot be false, and should be removed.
    Because it's not consistent with CTE semantic(CTE should not be init plan more than once).


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[GitHub] incubator-hawq issue #731: HAWQ-830. Fix wrong result in CTE query due to CT...

Posted by zhangh43 <gi...@git.apache.org>.

Github user zhangh43 commented on the issue:

    https://github.com/apache/incubator-hawq/pull/731
  
    We can keep this GUC gp_cte_sharing temporarily
    +1


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[GitHub] incubator-hawq issue #731: HAWQ-830. Fix wrong result in CTE query due to CT...

Posted by vraghavan78 <gi...@git.apache.org>.

Github user vraghavan78 commented on the issue:

    https://github.com/apache/incubator-hawq/pull/731
  
    gp_cte_sharing when set to true, the planner sometimes gets into a deadlock.


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[GitHub] incubator-hawq issue #731: HAWQ-830. Fix wrong result in CTE query due to CT...

Posted by xunzhang <gi...@git.apache.org>.

Github user xunzhang commented on the issue:

    https://github.com/apache/incubator-hawq/pull/731
  
    +1


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[GitHub] incubator-hawq issue #731: HAWQ-830. Fix wrong result in CTE query due to CT...

Posted by edespino <gi...@git.apache.org>.

Github user edespino commented on the issue:

    https://github.com/apache/incubator-hawq/pull/731
  
    @huor - Yes let's close this PR for now.  Thanks, -=e


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