tailieunhanh - Hướng dẫn học Microsoft SQL Server 2008 part 146

Nó cố gắng tìm các trang liên tiếp để cải thiện hiệu suất ghi. Mặc dù tôi đã liệt kê nó ở đây là bước 10, điều này có thể xảy ra ở bất kỳ điểm nào gần trong giao dịch hoặc sau nó tùy thuộc vào số lượng dữ liệu được thay đổi và gây áp lực với bộ nhớ trên hệ thống. SQL Server nhận được một tin nhắn viết''''hoàn toàn từ Windows. 11. | Part IX Performance Tuning and Optimization 10. In the background when a checkpoint occurs a SQL Server internal event or the lazy writer runs SQL Server writes any dirty modified data pages to the data file. It tries to find sequential pages to improve the performance of the write. Even though I ve listed it here as step 10 this can happen at nearly any point during the transaction or after it depending on the amount of data being changed and the memory pressure on the system. SQL Server receives a write complete message from Windows. 11. At the conclusion of the background write operation SQL Server marks the oldest open transaction in the transaction log. All older committed transactions have been confirmed in the data file and are now confirmed in the transaction log. The DBCC OpenTran command reports the oldest open transaction. Transaction complete The sequence comes full circle and returns the database to a consistent state. 12. The database finishes in a consistent state. Transaction-log rollback If the transaction is rolled back the DML operations are reversed in memory and a transaction-abort entry is made in the log. More often than not the time taken to perform a rollback will be greater than the time taken to make the changes in the first place. Transaction log recovery The primary benefit of a write-ahead transaction log is that it maintains the atomic transactional property in the case of system failure. If SQL Server should cease functioning perhaps due to a power failure or physical disaster the transaction log is automatically examined once it recovers as follows If any entries are in the log as DML operations but are not committed they are rolled back. To test this feature you must be brave. Begin a transaction and shut down the SQL server before issuing a COMMIT transaction using the Services applet . This does a shutdown with nowait. Simply closing Query Analyzer won t do it Query Analyzer will request permission to commit the pending .