Thursday, May 18, 2006

Synchronization stability

Data Port Sync is now undergoing a testing phase and although things are looking bright, I had overlooked one important detail: what happens when something fails?

There are four phases to the synchronization process: 1) preparation of the Access database; 2) exporting the Access database to the device in SDF format; 3) tracking changes on both ends and 4) merging the changes. When I designed the tracking code I assumed it would be okay to immediately mark the changes in the database, both in the user table and in the tracking table. As a matter of fact, this is a reasonable solution if you just want to track changed data, but it is not very safe if you need to process this information subsequently. If that process fails, you essentially lose the tracking information (at least with the way I was doing it).

To solve this issue, the data tracker now makes no change to the database. It generates a list of changed rows (for both databases) and the generation of this list is only affected by the posterior changes made to the database. The importance of this is that if the merge process fails, I can roll everything back and rerun the data tracker. All changes will be there.

Data Port Sync will become a product by the end of this month, before I go to MEDC Europe in Nice. Stay tuned.

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