Dbspace logging

The database server uses the following logging process for operations that involve data stored in dbspaces:

1. Reads the data page from disk to the shared-memory page buffer
2. Copies the unchanged page to the physical-log buffer, if required
3. Writes the new data to the page buffer and creates a logical-log record of the transaction, if required
4. Flushes the physical-log buffer to the physical log on disk
5. Flushes the logical-log buffer to a logical-log file on disk
6. Flushes the page buffer and writes it back to disk