DBMS Transactions and

Rollback Recovery

Helia / Martti Laiho

Control Buffers

Data Buffer (Buffer pool)

Log Buffer

Transaction Log files

- Connections- Transaction queueing- Locking List- etc

before image / after image

Table pagesand index pages x

Database Instance

Checkpoint:

Commit/Rollback:

Application programs - Sessions (connections) - Transactions - SQL commands

Helia / Martti Laiho, 1998-2003

DBMSListener / ServerTransaction ManagerSQL Engine (parser)Security ManagerQuery OptimizerConcurrency Manager (Lock Manager)Recovery ManagerRelational EngineMemory Manager

DBMSListener / ServerTransaction ManagerSQL Engine (parser)Security ManagerQuery OptimizerConcurrency Manager (Lock Manager)Recovery ManagerRelational EngineMemory Manager

LRU

x

Data file

Data fileFile ManagerFile Manager

Disk ManagerDisk Manager

read

write

write

Processing a Transaction

Insert into table

Update table

Delete from table

Select ..

Commit / Rollback

undo /redo data

undo / redo data

undo / redo data

commit / rollback

LGWR

OK ?

continue

User process: Data buffer Redo log buffer

Redo log files

(Rollback Segments -

Oracle only)

undo

undo data

undo data

?

On Rollback

before imagesafter images

Marking Checkpoint into Transaction Log

time

T1

T2

T3

T4

T5

Write Checkpointrecord into the log

of the current transactions

tc

Helia / Martti Laiho, 1998-2005

Commit

Rollback

Commit

Begin

Begin

Begin

Begin

Begin

Write all after imagesInto the database

A Soft Crash

time

T1

T2

T3

T4

T5

Checkpointrecord

SystemFailure

tctf

“Soft Crash”

Helia / Martti Laiho, 1998-2005

Commit

Rollback

Commit

Rollback recovery using transaction log

time

T1

T2

T3

T4

T5

Checkpointrecord

tctf

Rollback Recovery:

Undo list: T1, T2, T3 , T4, T5

Redo list: -

Helia / Martti Laiho, 1998-2005

Commit

Rollback

Commit

2. Find the last checkpoint record

3. Add transactions on undo list

1. Start up

From checkpointrecord

From the log after the checkpoint

Rollback recovery using transaction log

time

T1

T2

T3

T4

T5

Checkpointrecord

tctf

Rollback Recovery

Undo list: T1, T2, T3, T4, T5

Redo list: T1, T4

Helia / Martti Laiho, 1998-2005

Commit

Rollback

Commit

34. Move committed transactions to Redo list

Rollback recovery using transaction log

time

T1

T2

T3

T4

T5

Checkpointrecord

tc tf

Helia / Martti Laiho, 1998-2005

Commit

Rollback

Commit

Rollback Recovery

Undo list: T1, T2, T3, T4, T5

Redo list: T1, T4

5 5. Rollback transactions of the Undo list - writing the before images into the database Redo transactions of the Redo list - writing the after images into the database

6. Open the DBMS service to applications

undo

redo

redo

undo

undo