[GitHub] drill issue #701: DRILL-4963: Fix issues with dynamically loaded overloaded ...

[jinfengni <gi...@git.apache.org>]

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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