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Clase 11 manejo tablas modificada
This document discusses managing Oracle database tables. It covers how to create tables with different storage options, control space usage through parameters like PCTFREE and PCTUSED, analyze and retrieve table information from the data dictionary, and convert between ROWID formats. Functions of the DBMS_ROWID package allow accessing the components of a ROWID, like the object identifier, block number, and row number. Maintaining tables involves operations such as allocating and deallocating extents, truncating or dropping tables and columns.
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Clase 11 manejo tablas modificada
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- 2. Objectives After completing thislesson, you should be able to do the following: • Create tables using appropriate storage settings • Control the space used by tables • Analyze tables to check integrity and migration • Retrieve information about tables from the data dictionary • Convert between different formats of ROWID
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- 4. Structure of aRow Database block Row header Column length Column value
- 5. Oracle Data Types CHAR(N),NCHAR(N) VARCHAR2(N), NVARCHAR2(N) NUMBER(P,S) DATE RAW(N) BLOB, CLOB, NCLOB, BFILE LONG, LONG RAW ROWID, UROWID VARRAY TABLE REF Data type Built-inUser-defined Scalar RelationshipCollection
- 6. Data Types forStoring Large Objects LONG, LONG RAW Single column per table Up to 2 gigabytes SELECT returns data Data stored in-line No object type support Sequential access to chunks LOB Multiple columns per table Up to 4 gigabytes SELECT returns locator Data stored in-line or out-of-line Supports object types Random access to chunks
- 7. ROWID Data Type •Unique identifier for a row • Used to locate a row OOOOOO BBBBBBFFF RRR Data object number Relative file number Row numberBlock number ROWID Format
- 8. Restricted ROWID • Canidentify rows within a segment • Needs less space BBBBBBBB FFFFRRRR Block number Row number File number . .
- 9. Collections • Collections areobjects that contain objects. • VARRAYs are ordered sets of elements containing a count and a limit. • Nested tables are tables with a column or variable of the TABLE data type. VARRAY Nested table
- 10. Creating a Table CREATETABLE employee( id NUMBER(7), last_name VARCHAR2(25), dept_id NUMBER(7)) PCTFREE 20 PCTUSED 50 STORAGE(INITIAL 200K NEXT 200K PCTINCREASE 0 MAXEXTENTS 50) TABLESPACE data;
- 11. Temporary Tables • Therows are private to the session. • Tables retain data only for the duration of a transaction or session. • DML locks are not acquired on the data. • DMLs do not generate redo logs. ON COMMIT PRESERVE ROWS; CREATE GLOBAL TEMPORARY TABLE employee_temp AS SELECT * FROM employee;
- 12. Creating a Table:Guidelines • Use a few standard extent sizes for tables to reduce tablespace fragmentation. • Use locally managed tablespaces to avoid fragmentation. • Use the CACHE clause for frequently used, small tables.
- 13. Setting PCTFREE andPCTUSED • Compute PCTFREE (Average Row Size - Initial Row Size) * 100 Average Row Size • Compute PCTUSED Average Row Size * 100 100 - PCTFREE - Available Data Space
- 14. Row Migration andChaining Before update After update Pointer
- 15. Changing Storage andBlock Utilization Parameters ALTER TABLE summit.employee PCTFREE 30 PCTUSED 50 STORAGE(NEXT 500K MINEXTENTS 2 MAXEXTENTS 100);
- 16. Manually Allocating Extents ALTERTABLE summit.employee ALLOCATE EXTENT(SIZE 500K DATAFILE ‘/DISK3/DATA01.DBF’);
- 17. Nonpartitioned Table Reorganization ALTERTABLE employee MOVE TABLESPACE data1; • Moves data into a new segment while preserving indexes, constraints, privileges, and so on, on the table • Is being used to move a table to a different tablespace or to reorganize extents
- 18. Free space after delete Unusedblock Extent ID 0 1 2 3 4 Extent ID 0 1 2 3 4 Used block High-Water Mark After inserts: After deletes: High-water mark
- 19. Finding the High-WaterMark: DBMS_SPACE.UNUSED_SPACE Extent ID 0 1 2 3 4 High-water mark LAST_USED_EXTENT_FILE_ID, LAST_USED_EXTENT_BLOCK_ID TOTAL_BLOCKS UNUSED_BLOCKS
- 20. Free space after delete Unusedblock Before deallocation Used block Deallocation of Unused Space ALTER TABLE summit.employee DEALLOCATE UNUSED; After deallocation High-water mark Extent ID 43210 43210Extent ID
- 21. Truncating a Table TRUNCATETABLE summit.employee; Extent ID 0 1 High-water mark Free space
- 22. Dropping a Table DROPTABLE summit.department CASCADE CONSTRAINTS;
- 23. Dropping a Column ALTERTABLE employee DROP COLUMN comments CASCADE CONSTRAINTS CHECKPOINT 1000; Remove a column from a table • This removes the column length and data from each row, freeing space in the data block. • Dropping a column in a large table takes a considerable amount of time.
- 24. Using the UNUSEDOption ALTER TABLE orders SET UNUSED COLUMN comments CASCADE CONSTRAINTS; • Drop unused columns ALTER TABLE orders DROP UNUSED COLUMNS CHECKPOINT 1000; • Mark a column as unused • Continue to drop column operation ALTER TABLE orders DROP COLUMNS CONTINUE CHECKPOINT 1000;
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- 26. DBA_EXTENTS • OWNER • SEGMENT_NAME •EXTENT_ID • FILE_ID • BLOCK_ID • BLOCKS Retrieving Extent Information
- 27. DBMS_ROWID Package Function Name ROWID_CREATE ROWID_OBJECT ROWID_RELATIVE_FNO ROWID_BLOCK_NUMBER ROWID_ROW_NUMBER ROWID_TO_ABSOLUTE_FNO ROWID_TO_EXTENDED ROWID_TO_RESTRICTED Description Createsa ROWID from individual components Returns the object identifier for a ROWID Returns the relative file number for a ROWID Returns the block number for a ROWID Returns the row number for a ROWID Returns the absolute file number for a ROWID Converts a ROWID from restricted to extended Converts a ROWID from extended to restricted Commonly used functions:
- 28. Summary In this lesson,you should have learned how to: • Create a table with appropriate storage and block utilization parameters • Control table storage • Use the DBMS_ROWID package