同步机制，例如Java / Android中的Google云端硬盘

Question

I am trying to develop a mechanism for Sync data with app & server, like Google Drive/Dropbox for one of my android based application where data are stored locally on device and I would like to sync data with server.

Ways thought -

1) Observer which looks for change and call web service

2) Background service which runs in background and check for changes

3) Set Alarm which checks at particular time and sync all the data with server

I have not started to which option to go with, I would like to get experts view on this and like to get some guidance so that I can achieve the sync mechanism in best possible way for my app.

All suggestion are welcome.

Answer 1

Thinking on same line as you have been,the aim should be to achieve a balance between the number of times the server is queried for same set of information AND the data consistency.

for this, I would fire a GCM message from my server to the device for which the data on the server has changed, I would maintain a count for these Update Messages(No Notification genereated). If this count Exceeds the minimum-threshold-count-value, I would immediately call for an UPDATE. Or otherwise, if this count still is less than the threshold-count-value, for a certain period, that I would call the threshold-waiting-period, then too I call for an UPDATE.

The UPDATE would be using Sync Adapters and Services. This link explains its basics.

Hope this prooves to be helpful!

Answer 2

...so that I can achieve the sync mechanism in best possible way for my app

Well, the BEST mechanism depends completely on what kind of application, you are developing. Also, your option 1 and 2 seems very similar to me except few implementation changes. However, how frequently your device data is changing, that also matters a lot. If you have authentication mechanism, you can configure sync up, at the time, whenever you login to your app. Like in case of confidential data, sync up should happen immediately.

If data is managed well based on authentication and authorization based on user roles or so, you also need to take care of synchronization among them. For example, one user has updated an entity which is not yet sync and another user tries to update the same, then first user will see his changes are not synced or has been lost.

The best way (means having least drawbacks) to do this would be sync up trigger at a particular interval of time OR at every login time. (still as I said, depends on your app).

Hope this would clear some or all of your doubts.