When a jBASE application performs a database update, it writes to the log file (if active). It does this to a memory image and normally it is up to the platform file system to flush the memory image to disk every so often, by default on most platforms this is usually every minute.
You can use options in jlogadmin so that the jBASE processes themselves do this file synchronization more often. The default is every 10 seconds. This means in the event of a system failure, you will lose at the most 10 seconds worth of updates.
The use of the jlogsync program means this file synchronization is performed by the jlogsync process instead of individual jBASE processes and therefore alleviates the overhead of the synchronization from the update processes. Thus the jlogsync process is not mandatory, but in a large installation may provide performance gains.
jlogsync is available only on Unix platforms.