JDBC automatical query turned to be very slow

Question

I am maintaining an application creating an Oracle DB via JDBC. Starting from today this query:

SELECT  NULL                                                   AS         


        

Answer 1

The query in the question is generated by a call to java.sql.DatabaseMetaData.getExportedKeys() which delegates to oracle.jdbc.OracleDatabaseMetaData.getExportedKeys() to enumerate foreign keys referencing given table.

As stated in @Jon's answer, Oracle sometimes uses suboptimal plan for this query that may or may not be avoided by gathering statistics.

Other alternatives if the code can be changed:

• look at Easiest way to obtain database metadata in Java? for alternative implementation
• rewrite the query and call it directly

The second option was chosen by Liquibase project that used to call DatabaseMetaData in older versions. New versions use optimized query with proper joins from CORE-1844:

SELECT NULL AS pktable_cat, p.owner as pktable_schem, 
    p.table_name as pktable_name, pc.column_name as pkcolumn_name,    
    NULL as fktable_cat, f.owner as fktable_schem, f.table_name as fktable_name,    
    fc.column_name as fkcolumn_name, fc.position as key_seq, NULL as update_rule,    
    decode (f.delete_rule, 'CASCADE', 0, 'SET NULL', 2, 1) as delete_rule,    
    f.constraint_name as fk_name, p.constraint_name as pk_name,    
    decode(f.deferrable, 'DEFERRABLE', 5, 'NOT DEFERRABLE', 7, 'DEFERRED', 6) deferrability  
FROM    all_constraints p
INNER JOIN  all_cons_columns pc ON pc.owner = p.owner    
    AND pc.constraint_name = p.constraint_name    
    AND pc.table_name = p.table_name    
INNER JOIN all_constraints f ON p.owner = f.r_owner    
    AND p.constraint_name = f.r_constraint_name
INNER JOIN all_cons_columns fc ON fc.owner = f.owner    
    AND fc.constraint_name = f.constraint_name
    AND fc.table_name = f.table_name
    AND fc.position = pc.position
WHERE p.owner = :jdbcSchemaName
    AND p.constraint_type in ('P', 'U')    
    AND f.constraint_type = 'R'    
ORDER BY fktable_schem, fktable_name, key_seq