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From jinfengni <...@git.apache.org>
Subject [GitHub] drill issue #701: DRILL-4963: Fix issues with dynamically loaded overloaded ...
Date Thu, 02 Mar 2017 06:57:19 GMT
Github user jinfengni commented on the issue:

    https://github.com/apache/drill/pull/701
  
    +1
    
    I have one naive question. Before we dive into MVCC, or try to improve the current ZK-based
approach, have we consider adding a command "refresh function registry", so that users enforce
that function registry across the entire cluster is consistent? I remember someone (probably
@amansinha100 ) once brought up this idea.
    
    1. How often would user run into the issue caused by inconsistency of functions in different
drillbit?  Sounds like we are adding non-negligible overhead for other queries which do not
use dynamic UDF or overloaded functions, just for the sake of resolving issues of function
inconsistency.   
    2. Drill's function resolution logic not only happens in planning but also execution time
(due to the fact schema may be known in execution time). This means the function registry
could be checked multiple times during the query lifetime.  Adding overhead to each check
would slow down the entire query.
    3. With the "refresh function registry" command, use has a way to ensure function registry
is consistent after issuing such command. We could tell user that drillbit could run into
various of problems, before run "refresh function registry", therefore it's always recommend
to run such command after user creates a new UDF.
    



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