When you use the log-only synchronous method, update copying to the remote site is performed as follows:

• Update copying of database files is performed once during initial setup or when preparation for log application is performed.
• Update copying of system files is performed synchronously.

The log-only synchronous method updates a database by accepting transactions at the transaction execution site and by then performing update processing of the database at the log application site based on system logs copied from the transaction execution site. Normally, the main site is the transaction execution site, and the remote site is the log application site.

System log files and other information needed to recover a database are copied synchronously to guarantee that they are mirrored at the remote site. This means that if the HiRDB system at the main site terminates abnormally, the HiRDB system at the remote site can be restarted in the same status that the HiRDB system at the main site was in immediately preceding its abnormal termination. The log-only synchronous method is designed for use mainly in small to medium-sized systems.

Because copying of database files is performed once during initial setup or when preparation for log application is performed, the amount of communication traffic is generally less than with the other methods. This reduces adverse effects on transaction performance. Because the database at the remote site is updated based on system logs, the HiRDB at the remote site must always be operational.

Note

To use the log-only synchronous method, you must have installed the HiRDB Disaster Recovery Light Edition optional program product and have used the pdopsetup command to set it up.

Reference note

Although the log-only synchronous method generally requires less communication traffic than the other methods, this method is more difficult to use than the hybrid method.

The following figure provides an overview of the log-only synchronous method, and the table below it shows the processing methods used with the log-only synchronous method when update copying to the log application site is performed.

Figure 8-19 Overview of log-only synchronous method

Explanation

1. The database files are copied only during initial setup or when preparation for log application is performed; copying is not performed at other times.
2. Database update processing is performed by reading the logs that have been copied synchronously from the transaction execution site. This is called log application.
   

   Table 8-10 Processing methods when update copying is performed at the log application site (for the log-only synchronous method)

   Files copied to the log application site		Processing method used when update copying is performed
   Database files		Copied only during initial setup or when preparation for log application is performed.
   System file 1	System log files	Synchronous copy
   	Synchronization point dump file for transaction processing
   	Status file for transaction processing
   System file 2	Synchronization point dump file for log application processing	Not copied
   	Status file for log application processing

   Reference note

   The synchronization point dump file for transaction processing and status file for transaction processing are used in log application processing (they are the same synchronization point dump file and status file normally used in HiRDB operations). The synchronization point dump file for log application processing and status file for log application processing are used to obtain synchronization point dump and system status information while log application processing is being performed.

   Note

   Unlike the all synchronous, all asynchronous, and hybrid methods, the log-only synchronous method requires system file 2 (synchronization point dump file for log application processing and status file for log application processing). Therefore, take into account the need for these additional files when you configure the hardware.