Forensically Checking the State of Objects in an Oracle Database
During database operation, Oracle constantly accesses the data dictionary to validate schema objects and user access. Information from the data dictionary is stored in memory using the least recently used algorithm. Parsing information is typically stored in caches. COMMENTS columns describe table and column objects. Other Oracle products reference existing views and data dictionary tables, and may even create their own data dictionary tables. Whenever possible, application developers should refer to public synonyms when developing application logic. This way, the database is less likely to be affected by changes to the names of objects.
Objects are never invalidated
Invalid objects are objects that have been changed or deleted. An object may become invalid when a synonym has been deleted or recreated. If you attempt to access an invalid object, you will get an error message. To avoid this problem, you should regularly check the object's status. Invalid objects are often caused by improper database maintenance. Luckily, most invalid objects can be fixed by performing a simple action, such as recompilation.
You can forensically check the state of objects in an Oracle database by compiling them beforehand. The ALTER...COMPILE statement compiles individual objects, but you can also use the DBMS_UTILITY.COMPILE_SCHEMA statement to compile the entire schema. DBMS_UTILITY.COMPILE_SCHEMA is an alternative method. During the compilation process, you can specify whether or not to compile all objects or just invalid ones.
Objects are always valid
A schema object is never invalid when a reference to it is compiled into a table. This does not apply to dependencies between objects, such as tables. When a database object reference is compiled, it must have the expected structure. An invalid object cannot reference any other object. Therefore, any statement following a schema object must be compiled before execution. However, Oracle allows users to set up a signature capability for compiled remote objects. This capability affects only remote dependencies, not local dependencies.
Invalidation is automatically handled by the Oracle server. If an object changes its DML definition, Oracle invalidates its dependent objects. Similarly, if a table is dropped, it invalidates all dependent objects. This ensures that a table's structure is preserved. If an object is not created, Oracle automatically marks it as invalid. The same applies to a function-based index. Once an object is dropped or changed, it invalidates all dependencies on it.
While an object's status is important, a database object's value is not. It may have the same value if thousands of rows reference the same object. However, when it comes to index keys, Oracle provides two different indexes for the same key. In one case, a prefix entry references the base table while the suffix entry refers to the unique index entry. A suffix entry references a prefix entry, while the base table references a view, and every view referenced by it is stored with the same rowid. This process occurs recursively so that changes to the base table also affect the view.
Dependency checking is another feature that Oracle uses. Dependent objects are updated automatically when the referenced object changes. The database tracks these dependencies and marks them invalid when the referenced object changes. As a result, the referenced object must be recompiled against the new definition. This is automatically done when a referenced object is changed. For example, when a table refers to a table in a different database, a trigger might depend on a schema object from the same database. In a distributed database system, a remote stored procedure can call a table in another database.
Using the EXEC SQL FREE statement explicitly frees object cache memory when accessing large collections of non-referenceable objects or relational column object types. The SELECT statement applies to the entire department and sets of objects. The AT clause omits the EXEC SQL FREE statement. By default, the server will always use the default database connection. However, you can use this feature to make your database more reliable.
Using the SYS user privilege in Oracle, you can use this privilege. Then, use a connection for the SYS user and select the report of the invalid object. Objects in the database will be listed. Invalid objects will be listed on the Database Home page in Enterprise Manager. If the table does not contain an identifier, the SYS user will interpret the non-quoted identifier as uppercase and compare it with the quoted one.
When creating a table in an Oracle database, you must ensure that the name of the column is unique and has the right structure. A database object name should contain the table name, column name, datatype, and any other details that you want to store. Each row piece should include information regarding its precision and scale. These pieces are stored in a data block, and rows represent the collection of rows. It is also possible to use a table's prefix with an alias name.
An Oracle database uses the OCID type to store the uniqueness of a column. By using a unique identifier for an object, it prevents any mismatch between rows that have the same name. This is helpful for developers when designing a database and implementing its schema. The OCID type is especially useful when creating tables for multiple users. Oracle also supports a wide range of SQL functions.
Object views allow you to retrieve, update, insert, and delete relational data. These views also have columns defined as object datatypes, REFs, and collections. Inline views are not schema objects, but instead are subqueries with aliases that can be used as views within SQL statements. For example, if you want to retrieve a row from a view, you can use a derived table that contains the same column as the primary one.