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From paul-rogers <...@git.apache.org>
Subject [GitHub] drill pull request #923: DRILL-5723: Added System Internal Options That can ...
Date Fri, 01 Sep 2017 20:54:33 GMT
Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/923#discussion_r136656530
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/server/options/SystemOptionManager.java
---
    @@ -70,11 +69,13 @@
      *  </p>
      */
     
    -public class SystemOptionManager extends BaseOptionManager implements OptionManager,
AutoCloseable {
    +public class SystemOptionManager extends BaseOptionManager implements AutoCloseable {
       private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(SystemOptionManager.class);
     
    -  private CaseInsensitiveMap<OptionValidator> VALIDATORS;
    -  public void populateValidators() {
    +  public static final CaseInsensitiveMap<OptionValidator> DEFAULT_VALIDATORS =
    --- End diff --
    
    This change reverses a change made by Jyothsna. While it seems reasonable to create a
static table of validators, there is a subtle problem which Jyothsna's fix addressed.
    
    Under normal operation, we have exactly one Drillbit per process and thus exactly one
system option manager.
    
    But, we have unit tests that create multiple Drillbits per process. This is the most convenient
way to test concurrency issues in unit tests. In general, each Drillbit could define a different
default value for the system/session option; perhaps to check forward/backward compatibility
when the time comes to support rolling upgrades.
    
    In this model, each Drillbit will have a slightly different set of defaults. Thus, the
option validator table must be a member variable of the system option manager; it cannot be
global.
    
    Note also, in the existing tests with multiple Drillbits, a global table runs into a race
condition during reading defaults from the config file if we use a single table. But, if we
have a separate table per Drillbit, the race condition disappears.


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