TRANSACTION PROCESSING MONITOR OVERVIEW OF TPM FOR DISTRIBUTED TRANSACTION PROCESSING

Transcription

1 TPM Transaction Processing TPM Monitor TRANSACTION PROCESSING MONITOR OVERVIEW OF TPM FOR DISTRIBUTED TRANSACTION PROCESSING Peter R. Egli 1/9

2 Contents 1. What are Transaction Processing Monitors?. Properties of transactions 3. Two-Phase Commit architecture 4. Two-Phase Commit sequence 5. TPM structure /9

3 1. What are Transaction Processing Monitors (TPM)? Typical problem of distributed applications: Operations involving multiple databases () require transactional access. The operation is either successful or fails, but always has to leave all involved databases in a consistent state. Debit account Server 1 Transfer Credit account Server TPM: TPMs are an early solution for distributed transactions (booking systems, bank account transfers etc.). TPMs support distributed database transactions by coordinating multiple accesses. TPM Server 1 Server 3/9

4 . Properties of transactions (1/) Relational databases support ACID properties: 1. Atomicity. Consistency 3. Isolation 4. Durability Atomicity: Consistent state before & after transaction. Transfer Account CHF Account Consistency: No integrity constraint violations or Case 1: Successful transaction Case : Failed transaction Account 1 Account -1'000 CHF +1'000 CHF Account 1 Account -0 CHF +0 CHF Key Name balance_key 1 Egli 3 Müller 1 3 Meier 5 4 Huber 7 5 Gates Key balance 1.95 CHF 56'34'786'19.98 CHF CHF CHF 5 14'78 CHF Integrity violation (missing entry with key=7) 4/9

5 . Properties of transactions (/) Isolation: accesses are isolated from each other so they do not impact each other. Typically this is done with some sort of locking of resources (tables in ) and serialization of the requests. Request 1 Request Request Execution Execution Execution Time Durability: Transaction is persistent, even in case of errors (crash of, error etc.) Write to Write data to disk buffer Successful transaction Commit data to disk Crash of Failed transaction Commit data to disk after restart 5/9

6 3. Two-Phase Commit architecture TPMs employ a mechanism called Two-Phase Commit to support distributed transactions. Transaction (Coordinator): The coordinator serves as coordination point in the distributed transaction. : The resource s (aka "Cohort") perform the individual transactional accesses and are able to either commit or rollback an individual access. Undo / redo logs: Undo / redo logs are used by the transaction s for transactional access to their respective. (cohort) Undo/Redo logs interface for distributed transactions Transaction Manager (Coordinator) Undo/Redo logs (cohort) 6/9

7 4. Two-Phase Commit sequence (1/) A. Successful transaction: When all transaction s agree with the commit (vote "yes"), the transaction can be successfully committed. Transaction Manager 1 Request Query to commit Query to commit Commit request phase (=voting phase) 4 (agreement) 3 * Prepare for commit * Write undo / redo logs 3 * Prepare for commit * Write undo / redo logs 4 (agreement) 5 Commit Commit phase (=completion phase) 5 Commit 7 6 * Commit * Release all locks 6 * Commit * Release all locks 7 8 7/9

8 4. Two-Phase Commit sequence (/) A. Failed transaction: When either of the transaction does not positively acknowledge the transaction, the coordinator sends a rollback command to all transaction s. Transaction Manager 1 Request Query to commit Query to commit Commit request phase (=voting phase) 4 (agreement) 3 * Prepare for commit * Write undo / redo logs 3 * Prepare for commit * Write undo / redo logs 4 Not (or timeout) 5 Rollback Commit phase (=completion phase) 5 Rollback 7 6 * Undo transaction * Release all locks 6 * Undo transaction * Release all locks 7 8 Negative 8/9

9 Presentation TPM Transaction Processing Monitor 5. TPM structure TPMs represent complete systems akin to operating systems capable of running entire applications. s may be internal or external to the TPM. Request Queue Authentication E.g. transactional RPC XA interface=pc (X/Open) Service (application) TPM Response Queue Transaction Manager Log (undo/redo) Recovery Binding Scheduling Load Balancing Appl. Lifecycle 9/9