B Copyright © Oracle Corporation, 2002. All rights reserved. B Manually Managing Undo Data (Rollback Segments) Copyright © Oracle Corporation, 2002. All rights reserved. B-2 Objectives After completing this lesson, you should be able to do the following: • Create rollback segments using appropriate storage settings • Maintain rollback segments • Plan the number and size of rollback segments • Troubleshoot common rollback segment problems Copyright © Oracle Corporation, 2002. All rights reserved. B-3 Creating Rollback Segments CREATE ROLLBACK SEGMENT rbs01 TABLESPACE rbs STORAGE ( INITIAL 100K NEXT 100K MINEXTENTS 20 MAXEXTENTS 100 OPTIMAL 2000K ); Copyright © Oracle Corporation, 2002. All rights reserved. B-5 Transactions and Rollback Segments Transaction 1 Active extent Inactive extent 4 3 1 2 Transaction 2 Copyright © Oracle Corporation, 2002. All rights reserved. B-7 Growth of Rollback Segments Active extent Inactive extent 1 2 4 3 1 2 3 4 5 New extent Copyright © Oracle Corporation, 2002. All rights reserved. B-8 Shrinkage of Rollback Segments Active extent Inactive extent 1 2 6 3 1 2 3 4 5 6 OPTIMAL Copyright © Oracle Corporation, 2002. All rights reserved. B-9 Bringing Rollback Segments Online • Use the following command to make a rollback segment available: – • Specify the following initialization parameter to ensure that rollback segments are brought online at startup: ROLLBACK_SEGMENTS=(rbs01, rbs02) ALTER ROLLBACK SEGMENT rbs01 ONLINE; Copyright © Oracle Corporation, 2002. All rights reserved. B-10 How Instances Acquire Rollback Segments Bring all acquired rollback segments online. Acquire named private rollback segments. Are there enough RBS’s? Acquire public rollback segments. Compute the required number of rollback segments. Yes No Copyright © Oracle Corporation, 2002. All rights reserved. B-11 Changing Rollback Segment Storage Settings • Use the ALTER ROLLBACK SEGMENT command. • You can change OPTIMAL or MAXEXTENTS. ALTER ROLLBACK SEGMENT rbs01 STORAGE( MAXEXTENTS 200 ); Copyright © Oracle Corporation, 2002. All rights reserved. B-12 Deallocating Space From Rollback Segments • Use the ALTER ROLLBACK SEGMENT command. • If extents are active, they might not shrink to the requested size. ALTER ROLLBACK SEGMENT rbs01 SHRINK TO 4M; [...]... sessions Errors in taking a tablespace offline Copyright © Oracle Corporation, 2002 All rights reserved Insufficient Space for Transactions • No space in tablespace: – Extend data files – Enables automatic extension of data files – Add data files • MAXEXTENTS reached for segment – Increase MAXEXTENTS – Re-create segments with larger extent sizes B-18 Copyright © Oracle Corporation, 2002 All rights reserved . B Copyright © Oracle Corporation, 2002. All rights reserved. B Manually Managing Undo Data (Rollback Segments) Copyright © Oracle Corporation, 2002. All rights reserved. B-2 Objectives After. reserved. B-18 Insufficient Space for Transactions • No space in tablespace: – Extend data files – Enables automatic extension of data files – Add data files • MAXEXTENTS reached for segment – Increase MAXEXTENTS – Re-create