[jira] Created: (DERBY-1960) Handle null compilation schema to improve statement cache mechanism

["Yip Ng (JIRA)" <de...@db.apache.org>]

Handle null compilation schema to improve statement cache mechanism
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                 Key: DERBY-1960
                 URL: http://issues.apache.org/jira/browse/DERBY-1960
             Project: Derby
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 10.3.0.0
         Environment: Any
            Reporter: Yip Ng


A compilation schema with null value indicates that the trigger action statement text does not depend on the current schema. This means:

1. It is safe to compile this statement in any schema since there is no dependency with
    the CURRENT SCHEMA. i.e.: All relevent fields are qualified with a specific schema.

2. The statement cache mechanism can utilize this piece of information to enable
    better statement plan sharing across different schemas; thus, avoiding unnecessary
    statement compilation. 

This is a follow-up work of DERBY-630.  To improve the statement cache mechanism, the system needs to handle the null compilation schema in statement preparation logic.  It may require some work on the SQL parser to determine whether the compiled statement depends on the CURRENT SCHEMA or not, so that the compilation schema can be properly set. 


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