BACKUP OF THE DATA

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Partitions should be used for the behavioral information. This is usually, by far, the largest part of the data warehouse and is the most problematic to back up because of its sheer size . By placing the behavioral information into partitions based on dates, we can switch old partitions into a read-only mode. This means that no further data is expected to be placed into the partition and, therefore, once it is backed up, no further backups will be needed. Figure 7.10 shows the gathering of data into daily partitions.

Figure 7.10. Daily partitions.

Figure 7.10 shows a typical take-on of behavioral information into the warehouse using a partitioned approach. Each day has its own partition within the same physical table. Day (0) represents the latest data to be collected. Usually, this is yesterday's data. We cannot expect all of yesterday 's data to be available to us today. Delays in the transmission of data are inevitable. After three days in our example, however, all the data has been collected. Once a partition reaches the point at which all the data is deemed to have been received, it can be switched to read-only mode, which means that it is not expected to change again. At this point it can be backed up for the last time.

The backup strategy for behavioral data, in this example, is to make copies of Day (0) through to Day (-3) each day. Days (-4) backward are not required to be saved further.

Backup of circumstances data is slightly different. In most cases, the approach to be taken is, periodically, a full backup of the circumstances and, daily, a backup of the changes. Usually, the best way to backup changes is to copy the RDBMS transaction log files.

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