When we do any modification in the data, same will not be impacted in the physical table immediately. This follows a cycle to complete the action.
- Modify the data in buffer cache pages – Called ‘Logical write’.
- Write the same from buffer cache to physical table/disk and the same is recorded in the transaction log — Called ‘Physical write’.
The page which is modified in the buffer cache is called as a ‘Dirty page’. Dirty pages are copied to the disk in the physical write. Once the process of data modification is done to the disk, the dirty page will be removed.
Dirty pages are written to disk in 3 ways.
- Lazy writing
- Eager writing