Module org.jooq
Package org.jooq.impl

Class DefaultDiagnosticsListener

java.lang.Object
org.jooq.impl.DefaultDiagnosticsListener
All Implemented Interfaces:
DiagnosticsListener
public class DefaultDiagnosticsListener extends Object implements DiagnosticsListener
A publicly available default implementation of DiagnosticsListener.

Use this to stay compatible with future API changes (i.e. added methods to DiagnosticsListener)

Author:
Lukas Eder

  • Constructor Details

    • DefaultDiagnosticsListener

      public DefaultDiagnosticsListener()

  • Method Details

    • tooManyRowsFetched

      public void tooManyRowsFetched(DiagnosticsContext ctx)
      Description copied from interface: DiagnosticsListener
      The fetched JDBC ResultSet returned more rows than necessary.

      An event indicating that a JDBC ResultSet was fetched with A rows, but only B rows (B < A) were consumed.

      Typically, this problem can be remedied by applying the appropriate LIMIT clause in SQL, or SelectLimitStep.limit(int) clause in jOOQ.

      Specified by:
      tooManyRowsFetched in interface DiagnosticsListener

    • tooManyColumnsFetched

      public void tooManyColumnsFetched(DiagnosticsContext ctx)
      Description copied from interface: DiagnosticsListener
      The fetched JDBC ResultSet returned more columns than necessary.

      An event indicating that a JDBC ResultSet was fetched with A columns, but only B (B < A) were consumed.

      Typically, this problem can be remedied by not running a SELECT * query when this isn't strictly required.

      Specified by:
      tooManyColumnsFetched in interface DiagnosticsListener

    • unnecessaryWasNullCall

      public void unnecessaryWasNullCall(DiagnosticsContext ctx)
      Description copied from interface: DiagnosticsListener
      The fetched JDBC ResultSet returned a value for a column, on which ResultSet.wasNull() was called unnecessarily (more than once, or for a non-primitive type).
      Specified by:
      unnecessaryWasNullCall in interface DiagnosticsListener

    • missingWasNullCall

      public void missingWasNullCall(DiagnosticsContext ctx)
      Description copied from interface: DiagnosticsListener
      The fetched JDBC ResultSet returned a primitive type value for a column, which could have been null, but ResultSet.wasNull() was not called.
      Specified by:
      missingWasNullCall in interface DiagnosticsListener

    • duplicateStatements

      public void duplicateStatements(DiagnosticsContext ctx)
      Description copied from interface: DiagnosticsListener
      The executed JDBC statement has duplicates.

      Many databases maintain an execution plan cache, which remembers execution plans for a given SQL string. These caches often use the verbatim SQL string (or a hash thereof) as a key, meaning that "similar" but not identical statements will produce different keys. This may be desired in rare cases when querying skewed data, as a hack to force the optimiser to calculate a new plan for a given "similar" but not identical query, but mostly, this is not desirable as calculating execution plans can turn out to be expensive.

      Examples of such duplicate statements include:

      Whitespace differences

      
 SELECT * FROM  actor;
 SELECT  * FROM actor;

      Inline bind values

      
 SELECT * FROM actor WHERE id = 1;
 SELECT * FROM actor WHERE id = 2;

      Aliasing and qualification

      
 SELECT a1.* FROM actor a1 WHERE id = ?;
 SELECT * FROM actor a2 WHERE a2.id = ?;

      Examples of identical statements (which are not considered duplicate, but DiagnosticsListener.repeatedStatements(DiagnosticsContext), if on the same Connection) are: 

      
 SELECT * FROM actor WHERE id = ?;
 SELECT * FROM actor WHERE id = ?;

      This is a system-wide diagnostic that is not specific to individual Connection instances.

      Specified by:
      duplicateStatements in interface DiagnosticsListener

    • repeatedStatements

      public void repeatedStatements(DiagnosticsContext ctx)
      Description copied from interface: DiagnosticsListener
      The executed JDBC statement is repeated consecutively on the same JDBC Connection.

      This problem goes by many names, the most famous one being the N + 1 problem, when a single (1) query for a parent entity requires many (N) subsequent queries for child entities. This could have been prevented by rewriting the parent query to use a JOIN. If such a rewrite is not possible (or not easy), the subsequent N queries could at least profit (depending on the exact query):

      • From reusing the PreparedStatement
      • From being batched
      • From being re-written as a bulk fetch or write query

      This problem can be aggravated if combined with the DiagnosticsListener.duplicateStatements(DiagnosticsContext) problem, in case of which the repeated statements might not be diagnosed as easily.

      Repeated statements may or may not be "identical". In the following example, there are two repeated and identical statements: 

      
 SELECT * FROM actor WHERE id = ?;
 SELECT * FROM actor WHERE id = ?;

      In this example, we have three repeated statements, only some of which are also identical: 

      
 SELECT * FROM actor WHERE id = ?;
 SELECT * FROM actor WHERE id = ?;
 SELECT * FROM actor WHERE id =  ?;

      This is a Connection-specific diagnostic that is reset every time Connection.close() is called.

      Specified by:
      repeatedStatements in interface DiagnosticsListener