Handling of Failures-Coordinator Failure If coordinator fails while the commit protocol for T is executing then participating sites must decide on T's fate: 1.If an active site contains a <commit T>record in its log,then Tmust be committed. 2.If an active site contains an <abort T>record in its log,then T must be aborted. 3.If some active participating site does not contain a <ready T>record in its log,then the failed coordinator C cannot have decided to commit 7. Can therefore abort 7. 4.If none of the above cases holds,then all active sites must have a <ready 7>record in their logs,but no additional control records(such as <abort T>of <commit T>).In this case active sites must wait for C to recover,to find decision. Blocking problem:active sites may have to wait for failed coordinator to recover. Database System Concepts-7th Edition 23.12 @Silberschatz,Korth and SudarshanDatabase System Concepts - 7 23.12 ©Silberschatz, Korth and Sudarshan th Edition Handling of Failures- Coordinator Failure ▪ If coordinator fails while the commit protocol for T is executing then participating sites must decide on T’s fate: 1. If an active site contains a <commit T> record in its log, then T must be committed. 2. If an active site contains an <abort T> record in its log, then T must be aborted. 3. If some active participating site does not contain a <ready T> record in its log, then the failed coordinator Ci cannot have decided to commit T. Can therefore abort T. 4. If none of the above cases holds, then all active sites must have a <ready T> record in their logs, but no additional control records (such as <abort T> of <commit T>). In this case active sites must wait for Ci to recover, to find decision. ▪ Blocking problem: active sites may have to wait for failed coordinator to recover