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 pages and index pages x Database Instance Checkpoint: Commit/Rollback: Application programs - Sessions (connections) - Transactions - SQL commands Helia / Martti Laiho, DBMS Listener / Server Transaction Manager SQL Engine (parser) Security Manager Query Optimizer Concurrency Manager (Lock Manager) Recovery Manager Relational Engine Memory Manager DBMS Listener / Server Transaction Manager SQL Engine (parser) Security Manager Query Optimizer Concurrency Manager (Lock Manager) Recovery Manager Relational Engine Memory Manager LRU x Data file File Manager Disk Manager read write

Processing a Transaction Insert into table Update table Delete from table Select.. Commit / Rollback undo /redo data commit / rollback LGWR OK ? continue User process:Data bufferRedo log buffer Redo log files (Rollback Segments - Oracle only) undo undo data ? On Rollback before imagesafter images

Marking Checkpoint into Transaction Log time T1 T2 T3 T4 T5 Write Checkpoint record into the log of the current transactions tctc Helia / Martti Laiho, Commit Rollback Commit Begin Write all after images Into the database

A Soft Crash time T1 T2 T3 T4 T5 Checkpoint record System Failure tctc tftf “Soft Crash” Helia / Martti Laiho, Commit Rollback Commit

Rollback recovery using transaction log time T1 T2 T3 T4 T5 Checkpoint record tctc tftf Rollback Recovery: Undo list: T1, T2, T3, T4, T5 Redo list: - Helia / Martti Laiho, Commit Rollback Commit 2. Find the last checkpoint record 3. Add transactions on undo list 1. Start up From checkpoint record From the log after the checkpoint

Rollback recovery using transaction log time T1 T2 T3 T4 T5 Checkpoint record tctc tftf Rollback Recovery Undo list: T1, T2, T3, T4, T5 Redo list: T1, T4 Helia / Martti Laiho, Commit Rollback Commit 3 4. Move committed transactions to Redo list

Rollback recovery using transaction log time T1 T2 T3 T4 T5 Checkpoint record tctc tftf Helia / Martti Laiho, Commit Rollback Commit Rollback Recovery Undo list: T1, T2, T3, T4, T5 Redo list: T1, T 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 undo