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| Oracle8i Administrator's Guide Release 2 (8.1.6) Part Number A76956-01 |
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This chapter describes schema object management issues that are common across multiple types of schema objects. The following topics are presented:
For more information about syntax, authorizations, and restrictions for the SQL statements discussed in this chapter, see the Oracle8i SQL Reference.
See Also:
You can create several tables and views and grant privileges in one operation using the CREATE SCHEMA statement. The CREATE SCHEMA statement is useful if you want to guarantee the creation of several tables and views and grants in one operation. If an individual table, view or grant fails, the entire statement is rolled back. None of the objects are created, nor are the privileges granted.
Specifically, the CREATE SCHEMA statement can include CREATE TABLE, CREATE VIEW, and GRANT statements. You must have the privileges necessary to issue the included statements.
The following statement creates two tables and a view that joins data from the two tables:
CREATE SCHEMA AUTHORIZATION scott CREATE TABLE dept ( deptno NUMBER(3,0) PRIMARY KEY, dname VARCHAR2(15), loc VARCHAR2(25) CREATE TABLE emp ( empno NUMBER(5,0) PRIMARY KEY, ename VARCHAR2(15) NOT NULL, job VARCHAR2(10), mgr NUMBER(5,0), hiredate DATE DEFAULT (sysdate), sal NUMBER(7,2), comm NUMBER(7,2), deptno NUMBER(3,0) NOT NULL CONSTRAINT dept_fkey REFERENCES dept) CREATE VIEW sales_staff AS SELECT empno, ename, sal, comm FROM emp WHERE deptno = 30 WITH CHECK OPTION CONSTRAINT sales_staff_cnst GRANT SELECT ON sales_staff TO human_resources;
The CREATE SCHEMA statement does not support Oracle extensions to the ANSI CREATE TABLE and CREATE VIEW statements; this includes the STORAGE clause.
To rename an object, you must own it. You can rename schema objects in either of the following ways:
If you drop and re-create an object, all privileges granted for that object are lost. Privileges must be re-granted when the object is re-created.
Alternatively, a table, view, sequence, or a private synonym of a table, view, or sequence can be renamed using the RENAME statement. When using the RENAME statement, integrity constraints, indexes, and grants made for the object are carried forward for the new name. For example, the following statement renames the SALES_STAFF view:
RENAME sales_staff TO dept_30;
Before renaming a schema object, consider the following effects:
For more information about how Oracle manages object dependencies, see "Managing Object Dependencies".
You can analyze a table, index, or cluster to gather data about it, or to verify the validity of its storage format.
These schema objects can also be analyzed to collect or update statistics about specific objects. When a DML statement is issued, the statistics for the referenced objects are used to determine the most efficient execution plan for the statement. This optimization is called "cost-based optimization." The statistics are stored in the data dictionary.
A table, index, or cluster can be analyzed to validate the structure of the object. For example, in rare cases such as hardware or other system failures, an index can become corrupted and not perform correctly. When validating the index, you can confirm that every entry in the index points to the correct row of the associated table. If a schema object is corrupt, you can drop and re-create it.
A table or cluster can be analyzed to collect information about chained rows of the table or cluster. These results are useful in determining whether you have enough room for updates to rows. For example, this information can show whether PCTFREE is set appropriately for the table or cluster.
To analyze a table, cluster, or index, you must own the table, cluster, or index or have the ANALYZE ANY system privilege.
The following topics are discussed in this section:
For information specific to analyzing index-organized tables, see "Analyzing Index-Organized Tables".
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See Also:
For more information about analyzing tables, indexes, and clusters for performance statistics and the optimizer, see Oracle8i Designing and Tuning for Performance. |
Statistics about the physical storage characteristics of a table, index, or cluster can be gathered and stored in the data dictionary using the ANALYZE statement. Oracle can use these statistics when cost-based optimization is employed to choose the most efficient execution plan for SQL statements accessing analyzed objects. You can also use statistics generated by this statement to write efficient SQL statements that access analyzed objects.
You can choose either of the following clauses of the ANALYZE statement for gathering statistics:
When computing statistics, an entire object is scanned to gather data about the object. This data is used by Oracle to compute exact statistics about the object. Slight variances throughout the object are accounted for in these computed statistics. Because an entire object is scanned to gather information for computed statistics, the larger the size of an object, the more work that is required to gather the necessary information.
When estimating statistics, Oracle gathers representative information from portions of an object. This subset of information provides reasonable, estimated statistics about the object. The accuracy of estimated statistics depends upon how representative the sampling used by Oracle is. Only parts of an object are scanned to gather information for estimated statistics, so an object can be analyzed quickly. You can optionally specify the number or percentage of rows that Oracle should use in making the estimate.
The following statement computes statistics for the EMP table:
ANALYZE TABLE emp COMPUTE STATISTICS;
The following query estimates statistics on the EMP table, using the default statistical sample of 1064 rows:
ANALYZE TABLE emp ESTIMATE STATISTICS;
To specify the statistical sample that Oracle should use, include the SAMPLE option with the ESTIMATE STATISTICS option. You can specify an integer that indicates either a number of rows or index values, or a percentage of the rows or index values in the table. The following statements show examples of each option:
ANALYZE TABLE emp ESTIMATE STATISTICS SAMPLE 2000 ROWS; ANALYZE TABLE emp ESTIMATE STATISTICS SAMPLE 33 PERCENT;
In either case, if you specify a percentage greater than 50, or a number of rows or index values that is greater than 50% of those in the object, Oracle computes the exact statistics, rather than estimating.
If the data dictionary currently contains statistics for the specified object when an ANALYZE statement is issued, the new statistics replace the old statistics in the data dictionary.
This section lists the statistics that are gathered for tables, indexes, and clusters.
The only statistic that can be gathered for a cluster is the average cluster key chain length; this statistic can be estimated or computed. Statistics for tables in a cluster and all indexes associated with the cluster's tables (including the cluster key index) are automatically gathered when the cluster is analyzed for statistics.
Whether statistics for an object are computed or estimated, the statistics are stored in the data dictionary. The statistics can be queried using the following data dictionary views:
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See Also:
For more information about the data dictionary views containing statistics, see the Oracle8i Reference. |
You can remove statistics for a table, index, or cluster from the data dictionary using the ANALYZE statement with the DELETE STATISTICS option. For example, you might want to delete statistics for an object if you do not want cost-based optimization to be used for statements regarding the object. The following statement deletes statistics for the EMP table from the data dictionary:
ANALYZE TABLE emp DELETE STATISTICS;
Analyzing a table, cluster, or index can affect current shared SQL statements, which are statements currently in the shared pool. Whenever an object is analyzed to update or delete statistics, all shared SQL statements that reference the analyzed object are flushed from memory so that the next execution of the statement can take advantage of the new statistics.
There are some PL/SQL packages that allow you to effectively execute an ANALYZE statement. These are briefly discussed here.
This is a powerful package that allows both the gathering of statistics, including utilizing parallel execution, and the external manipulation of statistics. Statistics can be stored in tables outside of the data dictionary, where they can be manipulated without affecting the optimizer. Statistics can be copied between databases or backed up.
For information about using the DBMS_STATS package, see Oracle8i Designing and Tuning for Performance. For a description of procedures, syntax and exceptions, see Oracle8i Supplied PL/SQL Packages Reference.
This package contains the ANALYZE_SCHEMA procedure that takes two arguments: the name of a schema and an analysis method ('COMPUTE', 'ESTIMATE', or 'DELETE'). It gathers statistics on all of the objects in the schema.
For information on the DBMS_UTILITY package, see Oracle8i Supplied PL/SQL Packages Reference.
This package contains the ANALYZE_OBJECT procedure that takes four arguments: the type of object ('CLUSTER', 'TABLE', or 'INDEX'), the schema of the object, the name of the object, and an analysis method ('COMPUTE', 'ESTIMATE', or 'DELETE'). It gathers statistics on the object.
For information on the DBMS_DDL package, see Oracle8i Supplied PL/SQL Packages Reference.
To verify the integrity of the structure of a table, index, cluster, or snapshot, use the ANALYZE statement with the VALIDATE STRUCTURE option. If the structure is valid, no error is returned. However, if the structure is corrupt, you receive an error message. If a table, index, or cluster is corrupt, you should drop it and re-create it. If a snapshot is corrupt, perform a complete refresh and ensure that you have remedied the problem; if not, drop and re-create the snapshot.
The following statement analyzes the EMP table:
ANALYZE TABLE emp VALIDATE STRUCTURE;
You can validate an object and all related objects by including the CASCADE option. The following statement validates the EMP table and all associated indexes:
ANALYZE TABLE emp VALIDATE STRUCTURE CASCADE;
You can look at the chained and migrated rows of a table or cluster using the ANALYZE statement with the LIST CHAINED ROWS option. The results of this statement are stored in a specified table created explicitly to accept the information returned by the LIST CHAINED ROWS option.
To create an appropriate table to accept data returned by an ANALYZE...LIST CHAINED ROWS statement, use the UTLCHAIN.SQL script provided with Oracle. The UTLCHAIN.SQL script creates a table named CHAINED_ROWS in the schema of the user submitting the script.
After a CHAINED_ROWS table is created, you can specify it when using the ANALYZE statement. For example, the following statement inserts rows containing information about the chained rows in the EMP_DEPT cluster into the CHAINED_ROWS table:
ANALYZE CLUSTER emp_dept LIST CHAINED ROWS INTO chained_rows;
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See Also:
The name and location of the UTLCHAIN.SQL script are operating system-dependent; see your operating system-specific Oracle documentation. For more information about reducing the number of chained and migrated rows in a table or cluster, see Oracle8i Designing and Tuning for Performance. |
You can delete all rows of a table or all rows in a group of clustered tables so that the table (or cluster) still exists, but is completely empty. For example, you may have a table that contains monthly data, and at the end of each month, you need to empty it (delete all rows) after archiving its data.
To delete all rows from a table, you have the following three options:
You can delete the rows of a table using the DELETE statement. For example, the following statement deletes all rows from the EMP table:
DELETE FROM emp;
You can drop a table and then re-create the table. For example, the following statements drop and then re-create the EMP table:
DROP TABLE emp; CREATE TABLE emp ( . . . );
You can delete all rows of the table using the SQL statement TRUNCATE. For example, the following statement truncates the EMP table:
TRUNCATE TABLE emp;
If there are many rows present in a table or cluster when using the DELETE statement, significant system resources are consumed as the rows are deleted. For example, CPU time, redo log space, and rollback segment space from the table and any associated indexes require resources. Also, as each row is deleted, triggers can be fired. The space previously allocated to the resulting empty table or cluster remains associated with that object. With DELETE you can choose which rows to delete, whereas TRUNCATE and DROP wipe out the entire object.
When dropping and re-creating a table or cluster, all associated indexes, integrity constraints, and triggers are also dropped, and all objects that depend on the dropped table or clustered table are invalidated. Also, all grants for the dropped table or clustered table are dropped.
Using the TRUNCATE statement provides a fast, efficient method for deleting all rows from a table or cluster. A TRUNCATE statement does not generate any rollback information and it commits immediately; it is a DDL statement and cannot be rolled back. A TRUNCATE statement does not affect any structures associated with the table being truncated (constraints and triggers) or authorizations. A TRUNCATE statement also specifies whether space currently allocated for the table is returned to the containing tablespace after truncation.
You can truncate any table or cluster in the user's associated schema. Also, any user that has the DROP ANY TABLE system privilege can truncate a table or cluster in any schema.
Before truncating a table or clustered table containing a parent key, all referencing foreign keys in different tables must be disabled. A self-referential constraint does not have to be disabled.
As a TRUNCATE statement deletes rows from a table, triggers associated with the table are not fired. Also, a TRUNCATE statement does not generate any audit information corresponding to DELETE statements if auditing is enabled. Instead, a single audit record is generated for the TRUNCATE statement being issued. See Chapter 24, "Auditing Database Use", for information about auditing.
A hash cluster cannot be truncated. Also, tables within a hash or index cluster cannot be individually truncated; truncation of an index cluster deletes all rows from all tables in the cluster. If all the rows must be deleted from an individual clustered table, use the DELETE statement or drop and re-create the table.
The REUSE STORAGE or DROP STORAGE options of the TRUNCATE statement control whether space currently allocated for a table or cluster is returned to the containing tablespace after truncation. The default option, DROP STORAGE, reduces the number of extents allocated to the resulting table to the original setting for MINEXTENTS. Freed extents are then returned to the system and can be used by other objects.
Alternatively, the REUSE STORAGE option specifies that all space currently allocated for the table or cluster remains allocated to it. For example, the following statement truncates the EMP_DEPT cluster, leaving all extents previously allocated for the cluster available for subsequent inserts and deletes:
TRUNCATE CLUSTER emp_dept REUSE STORAGE;
The REUSE or DROP STORAGE option also applies to any associated indexes. When a table or cluster is truncated, all associated indexes are also truncated. Also note that the storage parameters for a truncated table, cluster, or associated indexes are not changed as a result of the truncation.
Database triggers are procedures that are stored in the database and activated ("fired") when specific conditions occur, such as adding a row to a table. You can use triggers to supplement the standard capabilities of Oracle to provide a highly customized database management system. For example, you can create a trigger to restrict DML operations against a table, allowing only statements issued during regular business hours.
Database triggers can be associated with a table, schema, or database. They are implicitly fired when:
For a full list of statements and database events that will cause triggers to fire, see Oracle8i SQL Reference.
Triggers are created with the CREATE TRIGGER statement. They can be defined as firing BEFORE or AFTER the triggering event, or INSTEAD OF it. The following statement creates a trigger SCOTT.EMP_PERMIT_CHANGES on table SCOTT.EMP. The trigger will fire, before any of the specified statements are executed.
CREATE TRIGGER scott.emp_permit_changes BEFORE DELETE OR INSERT OR UPDATE ON scott.emp . pl/sql block .
You can later remove a trigger from the database by issuing the DROP TRIGGER statement.
Information on creating and using triggers is contained in Oracle8i Application Developer's Guide - Fundamentals.
A trigger can be in either of two distinct modes:
To enable or disable triggers using the ALTER TABLE statement, you must own the table, have the ALTER object privilege for the table, or have the ALTER ANY TABLE system privilege. To enable or disable an individual trigger using the ALTER TRIGGER statement, you must own the trigger or have the ALTER ANY TRIGGER system privilege.
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See Also:
For a description of triggers, see Oracle8i Concepts. For syntax, restrictions, and specific authorization requirements for the SQL statements used to create and manage triggers, see Oracle8i SQL Reference. |
You enable a disabled trigger using the ALTER TRIGGER statement with the ENABLE option. To enable the disabled trigger named REORDER on the INVENTORY table, enter the following statement:
ALTER TRIGGER reorder ENABLE;
To enable all triggers defined for a specific table, use the ALTER TABLE statement with the ENABLE ALL TRIGGERS option. To enable all triggers defined for the INVENTORY table, enter the following statement:
ALTER TABLE inventory ENABLE ALL TRIGGERS;
You may want to temporarily disable a trigger if one of the following conditions is true:
You disable a trigger using the ALTER TRIGGER statement with the DISABLE option. To disable the trigger REORDER on the INVENTORY table, enter the following statement:
ALTER TRIGGER reorder DISABLE;
You can disable all triggers associated with a table at the same time using the ALTER TABLE statement with the DISABLE ALL TRIGGERS option. For example, to disable all triggers defined for the INVENTORY table, enter the following statement:
ALTER TABLE inventory DISABLE ALL TRIGGERS;
Integrity constraints are rules that restrict the values for one or more columns in a table. Constraint clauses can appear in either CREATE TABLE or ALTER TABLE statements, and identify the column or columns affected by the constraint and identify the conditions of the constraint.
This following topics are included in this section:
This book briefly discusses the concepts of constraints and identifies the SQL statements used to define and manage integrity constraints. For a more thorough discussion of integrity constraints, see Oracle8i Concepts. For detailed information and examples of using integrity constraints in applications, see Oracle8i Application Developer's Guide - Fundamentals.
See Also:
You may specify that a constraint is enabled (ENABLE) or disabled (DISABLE). If a constraint is enabled, data is checked as it is entered or updated in the database, and data that does not conform to the constraint's rule is prevented from being entered. If a constraint is disabled, then data that does not conform can be allowed to enter the database.
Additionally, you can specify that existing data in the table must conform to the constraint (VALIDATE). Conversely, if you specify NOVALIDATE, you are not ensured that existing data conforms.
An integrity constraint defined on a table can be in one of the following states:
For details about the meaning of these states and an understanding of their consequences, see the Oracle8i SQL Reference. Some of these consequences are discussed here.
To enforce the rules defined by integrity constraints, the constraints should always be enabled. However, you may wish to temporarily disable the integrity constraints of a table for the following performance reasons:
In all three cases, temporarily disabling integrity constraints can improve the performance of the operation, especially in data warehouse configurations.
It is possible to enter data that violates a constraint while that constraint is disabled. Thus, you should always enable the constraint after completing any of the operations listed in the bullets above.
While a constraint is enabled, no row violating the constraint can be inserted into the table. However, while the constraint is disabled such a row can be inserted; this row is known as an exception to the constraint. If the constraint is in the enable novalidated state, violations resulting from data entered while the constraint was disabled remain. The rows that violate the constraint must be either updated or deleted in order for the constraint to be put in the validated state.
You can identify exceptions to a specific integrity constraint while attempting to enable the constraint. See "Reporting Constraint Exceptions". All rows violating constraints will be put onto an EXCEPTIONS table, which you can examine.
When a constraint is in the enable novalidate state, all subsequent statements are checked for conformity to the constraint; however, any existing data in the table is not checked. A table with enable novalidated constraints can contain invalid data, but it is not possible to add new invalid data to it. Enabling constraints in the novalidated state is most useful in data warehouse configurations that are uploading valid OLTP data.
Enabling a constraint does not require validation. Enabling a constraint novalidate is much faster than enabling and validating a constraint. Also, validating a constraint that is already enabled does not require any DML locks during validation (unlike validating a previously disabled constraint). Enforcement guarantees that no violations are introduced during the validation. Hence, enabling without validating enables you to reduce the downtime typically associated with enabling a constraint.
Using integrity constraint states in the following order can ensure the best benefits:
Some benefits of using constraints in this order are:
When an integrity constraint is defined in a CREATE TABLE or ALTER TABLE statement, it can be enabled, disabled, or validated or not validated as determined by your specification of the ENABLE/DISABLE clause. If the ENABLE/DISABLE clause is not specified in a constraint's definition, Oracle automatically enables and validates the constraint.
The following CREATE TABLE and ALTER TABLE statements both define and disable integrity constraints:
CREATE TABLE emp ( empno NUMBER(5) PRIMARY KEY DISABLE, . . . ; ALTER TABLE emp ADD PRIMARY KEY (empno) DISABLE;
An ALTER TABLE statement that defines and disables an integrity constraint never fails because of rows of the table that violate the integrity constraint. The definition of the constraint is allowed because its rule is not enforced.
For information about constraint exceptions, see "Reporting Constraint Exceptions" .
The following CREATE TABLE and ALTER TABLE statements both define and enable integrity constraints:
CREATE TABLE emp ( empno NUMBER(5) CONSTRAINT emp.pk PRIMARY KEY, . . . ; ALTER TABLE emp ADD CONSTRAINT emp.pk PRIMARY KEY (empno);
An ALTER TABLE statement that defines and attempts to enable an integrity constraint may fail because rows of the table may violate the integrity constraint. In this case, the statement is rolled back and the constraint definition is not stored and not enabled.
To enable a UNIQUE key or PRIMARY KEY, which creates an associated index, the owner of the table also needs a quota for the tablespace intended to contain the index, or the UNLIMITED TABLESPACE system privilege.
You can use the ALTER TABLE statement to enable, disable or modify a constraint.
The following statements disable integrity constraints:
ALTER TABLE dept DISABLE CONSTRAINT dname_ukey; ALTER TABLE dept DISABLE PRIMARY KEY, DISABLE UNIQUE (dname, loc);
The following statements enable novalidate disabled integrity constraints:
ALTER TABLE dept ENABLE NOVALIDATE CONSTRAINT dname_ukey; ALTER TABLE dept ENABLE NOVALIDATE PRIMARY KEY, ENABLE NOVALIDATE UNIQUE (dname, loc);
The following statements enable or validate disabled integrity constraints:
ALTER TABLE dept MODIFY CONSTRAINT dname_key VALIDATE; ALTER TABLE dept MODIFY PRIMARY KEY ENABLE NOVALIDATE;
The following statements enable disabled integrity constraints:
ALTER TABLE dept ENABLE CONSTRAINT dname_ukey; ALTER TABLE dept ENABLE PRIMARY KEY, ENABLE UNIQUE (dname, loc);
To disable or drop a UNIQUE key or PRIMARY KEY constraint and all dependent FOREIGN KEY constraints in a single step, use the CASCADE option of the DISABLE or DROP clauses. For example, the following statement disables a PRIMARY KEY constraint and any FOREIGN KEY constraints that depend on it:
ALTER TABLE dept DISABLE PRIMARY KEY CASCADE;
When Oracle checks a constraint, it signals an error if the constraint is not satisfied. You can defer checking the validity of constraints until the end of a transaction.
When you issue the SET CONSTRAINTS statement, the SET CONSTRAINTS mode lasts for the duration of the transaction, or until another SET CONSTRAINTS statement resets the mode.
Within the application being used to manipulate the data, you must set all constraints deferred before you actually begin processing any data. Use the following DML statement to set all deferrable constraints deferred:
SET CONSTRAINTS ALL DEFERRED;
You can check for constraint violations before committing by issuing the SET CONSTRAINTS ALL IMMEDIATE statement just before issuing the COMMIT. If there are any problems with a constraint, this statement will fail and the constraint causing the error will be identified. If you commit while constraints are violated, the transaction will be rolled back and you will receive an error message.
When you create a UNIQUE or PRIMARY key, Oracle checks to see if an existing index can be used to enforce uniqueness for the constraint. If there is no such index, Oracle creates one.
When Oracle is using a unique index to enforce a constraint, and constraints associated with the unique index are dropped or disabled, the index is dropped.
While enabled foreign keys reference a PRIMARY or UNIQUE key, you cannot disable or drop the PRIMARY or UNIQUE key constraint or the index.
You can drop an integrity constraint if the rule that it enforces is no longer true, or if the constraint is no longer needed. You can drop the constraint using the ALTER TABLE statement with the DROP clause. The following two statements drop integrity constraints:
ALTER TABLE dept DROP UNIQUE (dname, loc); ALTER TABLE emp DROP PRIMARY KEY, DROP CONSTRAINT dept_fkey;
Dropping UNIQUE key and PRIMARY KEY constraints drops the associated unique indexes. Also, if FOREIGN KEYs reference a UNIQUE or PRIMARY KEY, you must include the CASCADE CONSTRAINTS clause in the DROP statement, or you cannot drop the constraint.
If exceptions exist when a constraint is validated, an error is returned and the integrity constraint remains novalidated. When a statement is not successfully executed because integrity constraint exceptions exist, the statement is rolled back. If exceptions exist, you cannot validate the constraint until all exceptions to the constraint are either updated or deleted.
You cannot use the CREATE TABLE statement to determine which rows are in violation. To determine which rows violate the integrity constraint, issue the ALTER TABLE statement with the EXCEPTIONS option in the ENABLE clause. The EXCEPTIONS option places the ROWID, table owner, table name, and constraint name of all exception rows into a specified table.
The following statement attempts to validate the PRIMARY KEY of the DEPT table, and if exceptions exist, information is inserted into a table named EXCEPTIONS:
ALTER TABLE dept ENABLE PRIMARY KEY EXCEPTIONS INTO exceptions;
If duplicate primary key values exist in the DEPT table and the name of the PRIMARY KEY constraint on DEPT is SYS_C00610, the following rows might be placed in the table EXCEPTIONS by the previous statement:
SELECT * FROM exceptions; ROWID OWNER TABLE_NAME CONSTRAINT ------------------ --------- -------------- ----------- AAAAZ9AABAAABvqAAB SCOTT DEPT SYS_C00610 AAAAZ9AABAAABvqAAG SCOTT DEPT SYS_C00610
A more informative query would be to join the rows in an exception report table and the master table to list the actual rows that violate a specific constraint, as shown in the following example:
SELECT deptno, dname, loc FROM dept, exceptions WHERE exceptions.constraint = 'SYS_C00610' AND dept.rowid = exceptions.row_id; DEPTNO DNAME LOC ---------- -------------- ----------- 10 ACCOUNTING NEW YORK 10 RESEARCH DALLAS
All rows that violate a constraint must be either updated or deleted from the table containing the constraint. When updating exceptions, you must change the value violating the constraint to a value consistent with the constraint or a null. After the row in the master table is updated or deleted, the corresponding rows for the exception in the exception report table should be deleted to avoid confusion with later exception reports. The statements that update the master table and the exception report table should be in the same transaction to ensure transaction consistency.
To correct the exceptions in the previous examples, you might issue the following transaction:
UPDATE dept SET deptno = 20 WHERE dname = 'RESEARCH'; DELETE FROM exceptions WHERE constraint = 'SYS_C00610'; COMMIT;
When managing exceptions, the goal is to eliminate all exceptions in your exception report table.
This section describes the various object dependencies, and includes the following topics:
First, review Table 19-1, which shows how objects are affected by changes in other objects on which they depend.
Oracle automatically recompiles an invalid view or PL/SQL program unit the next time it is used. In addition, a user can force Oracle to recompile a view or program unit using the appropriate SQL statement with the COMPILE clause. Forced compilations are most often used to test for errors when a dependent view or program unit is invalid, but is not currently being used. In these cases, automatic recompilation would not otherwise occur until the view or program unit was executed. To identify invalid dependent objects, query the views USER_/ALL_/DBA_OBJECTS.
To recompile a view manually, you must have the ALTER ANY TABLE system privilege or the view must be contained in your schema. Use the ALTER VIEW statement with the COMPILE clause to recompile a view. The following statement recompiles the view EMP_DEPT contained in your schema:
ALTER VIEW emp_dept COMPILE;
To recompile a stand-alone procedure manually, you must have the ALTER ANY PROCEDURE system privilege or the procedure must be contained in your schema. Use the ALTER PROCEDURE/FUNCTION statement with the COMPILE clause to recompile a stand-alone procedure or function. The following statement recompiles the stored procedure UPDATE_SALARY contained in your schema:
ALTER PROCEDURE update_salary COMPILE;
To recompile a package manually, you must have the ALTER ANY PROCEDURE system privilege or the package must be contained in your schema. Use the ALTER PACKAGE statement with the COMPILE clause to recompile either a package body or both a package specification and body. The following statements recompile just the body, and the body and specification of the package ACCT_MGMT, respectively:
ALTER PACKAGE acct_mgmt COMPILE BODY; ALTER PACKAGE acct_mgmt COMPILE PACKAGE;
This section describes how Oracle resolves an object name.
If no schema is found in Step c, the object cannot be qualified and Oracle returns an error.
When global object names are used in a distributed database, either explicitly or indirectly within a synonym, the local Oracle resolves the reference locally. For example, it resolves a synonym to a remote table's global object name. The partially resolved statement is shipped to the remote database, and the remote Oracle completes the resolution of the object as described here.
This section describes aspects of changing data dictionary storage parameters, and includes the following topics:
If your database is very large or contains an unusually large number of objects, columns in tables, constraint definitions, users, or other definitions, the tables that make up the data dictionary might at some point be unable to acquire additional extents. For example, a data dictionary table may need an additional extent, but there is not enough contiguous space in the SYSTEM tablespace. If this happens, you cannot create new objects, even though the tablespace intended to hold the objects seems to have sufficient space. To remedy this situation, you can change the storage parameters of the underlying data dictionary tables to allow them to be allocated more extents, in the same way that you can change the storage settings for user-created segments. For example, you can adjust the values of NEXT or PCTINCREASE for the data dictionary table.
The following tables and clusters contain the definitions of all the user-created objects in the database:
Of all of the data dictionary segments, the following are the most likely to require change:
For the clustered tables, you must change the storage settings for the cluster, not for the table.
Oracle returns an error if a user tries to create a new object that requires Oracle to allocate an additional extent to the data dictionary when it is unable to allocate an extent. The error message ORA-1653, "failed to allocate extent of size num in tablespace 'name'" indicates this kind of problem.
If you receive this error message and the segment you were trying to change (such as a table or rollback segment) has not reached the limits specified for it in its definition, check the storage settings for the object that contains its definition.
For example, if you received an ORA-1547 while trying to define a new PRIMARY KEY constraint on a table and there is sufficient space for the index that Oracle must create for the key, check if CON$ or C_COBJ# cannot be allocated another extent; to do this, query DBA_SEGMENTS and consider changing the storage parameters for CON$ or C_COBJ#.
For more information, see "Example 7: Displaying Segments that Cannot Allocate Additional Extents".
The data dictionary provides many views about the schema objects described in this book. The following list summarizes the views associated with schema objects:
The following data dictionary views contain information about the segments of a database:
The following data dictionary views contain information about a database's extents:
Additionally, the following Oracle supplied PL/SQL packages provide information about space usage and free blocks in objects:
The following examples demonstrate ways to display miscellaneous schema objects.
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See Also:
For a complete description of data dictionary views, see Oracle8i Reference. For a description of PL/SQL packages, see Oracle8i Supplied PL/SQL Packages Reference. |
The following query lists all of the objects owned by the user issuing the query:
SELECT object_name, object_type FROM user_objects; OBJECT_NAME OBJECT_TYPE ------------------------- ------------------- EMP_DEPT CLUSTER EMP TABLE DEPT TABLE EMP_DEPT_INDEX INDEX PUBLIC_EMP SYNONYM EMP_MGR VIEW
Column information, such as name, datatype, length, precision, scale, and default data values can be listed using one of the views ending with the _COLUMNS suffix. For example, the following query lists all of the default column values for the EMP and DEPT tables:
SELECT table_name, column_name, data_default FROM user_tab_columns WHERE table_name = 'DEPT' OR table_name = 'EMP'; TABLE_NAME COLUMN_NAME DATA_DEFAULT ---------- ------------- -------------------- DEPT DEPTNO DEPT DNAME DEPT LOC 'NEW YORK' EMP EMPNO EMP ENAME EMP JOB EMP MGR EMP HIREDATE SYSDATE EMP SAL EMP COMM EMP DEPTNO
Notice that not all columns have user-specified defaults. These columns automatically have NULL as the default.
When you create a view or a synonym, the view or synonym is based on its underlying base object. The ALL/USER/DBA_DEPENDENCIES data dictionary views can be used to reveal the dependencies for a view and the ALL/USER/DBA_SYNONYMS data dictionary views can be used to list the base object of a synonym. For example, the following query lists the base objects for the synonyms created by the user JWARD:
SELECT table_owner, table_name, synonym_name FROM sys.dba_synonyms WHERE owner = 'JWARD'; TABLE_OWNER TABLE_NAME SYNONYM_NAME ---------------------- ----------- ----------------- SCOTT DEPT DEPT SCOTT EMP EMP
The following query returns the name of each rollback segment, the tablespace that contains each, and the size of each rollback segment:
SELECT segment_name, tablespace_name, bytes, blocks, extents FROM sys.dba_segments WHERE segment_type = 'ROLLBACK'; SEGMENT_NAME TABLESPACE_NAME BYTES BLOCKS EXTENTS ------------ --------------- --------- ------- --------- RS1 SYSTEM 20480 10 2 RS2 TS1 40960 20 3 SYSTEM SYSTEM 184320 90 3
General information about the currently allocated extents in a database is stored in the DBA_EXTENTS data dictionary view. For example, the following query identifies the extents associated with rollback segments and the size of each of those extents:
SELECT segment_name, bytes, blocks FROM sys.dba_extents WHERE segment_type = 'ROLLBACK'; SEGMENT_NAME BYTES BLOCKS --------------- --------- -------- RS1 10240 5 RS1 10240 5 SYSTEM 51200 25 SYSTEM 51200 25 SYSTEM 51200 25
Notice that the RS1 rollback segment is comprised of two extents, both 10K, while the SYSTEM rollback segment is comprised of three equally sized extents of 50K.
Information about the free extents (extents not allocated to any segment) in a database is stored in the DBA_FREE_SPACE data dictionary view. For example, the following query reveals the amount of free space available via free extents in each tablespace:
SELECT tablespace_name, file_id, bytes, blocks FROM sys.dba_free_space; TABLESPACE_NAME FILE_ID BYTES BLOCKS ------------------- --------- -------- ---------- SYSTEM 1 8120320 3965 SYSTEM 1 10240 5 TS1 2 10432512 5094
You can also use DBA_FREE_SPACE, in combination with the views DBA_SEGMENTS, DBA_TABLES, DBA_CLUSTERS, DBA_INDEXES, and DBA_ROLLBACK_SEGS, to determine if any other segment is unable to allocate additional extents for data dictionary objects only.
A segment may not be allocated to an extent for any of the following reasons:
The following query returns the names, owners, and tablespaces of all segments that fit any of the above criteria:
SELECT seg.owner, seg.segment_name, seg.segment_type, seg.tablespace_name, DECODE(seg.segment_type, 'TABLE', t.next_extent, 'CLUSTER', c.next_extent, 'INDEX', i.next_extent, 'ROLLBACK', r.next_extent) FROM sys.dba_segments seg, sys.dba_tables t, sys.dba_clusters c, sys.dba_indexes i, sys.dba_rollback_segs r WHERE ((seg.segment_type = 'TABLE' AND seg.segment_name = t.table_name AND seg.owner = t.owner AND NOT EXISTS (SELECT tablespace_name FROM dba_free_space free WHERE free.tablespace_name = t.tablespace_name AND free.bytes >= t.next_extent)) OR (seg.segment_type = 'CLUSTER' AND seg.segment_name = c.cluster_name AND seg.owner = c.owner AND NOT EXISTS (SELECT tablespace_name FROM dba_free_space free WHERE free.tablespace_name = c.tablespace_name AND free.bytes >= c.next_extent)) OR (seg.segment_type = 'INDEX' AND seg.segment_name = i.index_name AND seg.owner = i.owner AND NOT EXISTS (SELECT tablespace_name FROM dba_free_space free WHERE free.tablespace_name = i.tablespace_name AND free.bytes >= i.next_extent)) OR (seg.segment_type = 'ROLLBACK' AND seg.segment_name = r.segment_name AND seg.owner = r.owner AND NOT EXISTS (SELECT tablespace_name FROM dba_free_space free WHERE free.tablespace_name = r.tablespace_name AND free.bytes >= r.next_extent))) OR seg.extents = seg.max_extents OR seg.extents = data_block_size;
Once you have identified a segment that cannot allocate additional extents, you can solve the problem in either of two ways, depending on its cause:
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