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Data Consistency, Recovery, and Migration 4-19
Dbspace Logging
Dbspace Logging
OnLine logs dbspace data operations in six steps, illustrated in Figure 4-1 on
page 4-20.
Following is an overview of steps in logging dbspace data:
1. Read the data page from disk to shared-memory page buffer.
2. Copy the unchanged page to the physical log buffer.
3. Write the new data into the page buffer; create a logical log record of
the transaction, if needed.
4. Flush physical log buffer to the physical log on disk.
5. Flush logical log buffer to a logical log file on disk.
6. Flush the page buffer and write it back to disk.