[jira] [Commented] (DERBY-5684) Explore possible istat daemon improvements and optimizations

    [ https://issues.apache.org/jira/browse/DERBY-5684?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13273654#comment-13273654 ]

Dag H. Wanvik commented on DERBY-5684:
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Looked at the latest patch - seems to do what you describe to me :) Some comments and questions:

FromBaseTable:

- for (int i=0; i < cds.length; i++) {                          
      ConglomerateDescriptor tmpCd = cds[i];                    
      if (tmpCd.isIndex()) {                                    
          IndexRowGenerator irg = tmpCd.getIndexDescriptor();  
          // The case where we have a table with a              
          // single-column primary key/index is pretty          
          // common, so avoid engaging the istat daemon.        
          if (!irg.isUnique() ||                                
                  irg.numberOfOrderedColumns() > 1) {          
              qualified = true;                                
              break;                                            
          }                                                    
      }                                                        
  }                                                            

  I think I'd reverse the logic here for clarity to:

  for (int i=0; i < cds.length; i++) {                          
      ConglomerateDescriptor tmpCd = cds[i];                    
      if (tmpCd.isIndex()) {                                    
          IndexRowGenerator irg = tmpCd.getIndexDescriptor();  
          // The case where we have a table with a              
          // single-column primary key/index is pretty          
          // common, so avoid engaging the istat daemon.
          if (irg.isUnique() && irg.numberOfOrderedColumns() == 1) {
              continue;
          }

          qualified = true;                                
          break;        
      }                                                        
  }                                                            


- IndexStatisticsAnalyzer:
> Without this restriction the algorithm will drop valid statistics entries.
Change wording to "would drop".

Essentially a set: qualifiedCds, implement as such? (e.g. "contains" predicate cleaner than a search loop).

What scenario corresponds to this latter case below (irg == null):?

if (!cd.isIndex() || irg == null) {
    return DISQUALIFIED;
}

- IndexStatisticsDaemonImpl:

// TODO: Is it ok to always invalidate, or should logic be different
//       for background and explicit mode?

What are the pros and cons here? I would assume both should invalidate?

               
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