Synchronization

Object Synchronization project

This is just a simple project to play a bit with IRIS Object Synchronization feature (also available in last versions in Caché and Ensemble). On the journey you can also see a sample of an Installer class that would allow you, from scratch, to define and create Namespaces + Databases, REST services, import a class model and populate it with sample data.

WARNING: As usual… be aware this is playing code, not robust enough for any production use.

Data Model

The data itself is very simple, just 8 classes:

Install and Get Ready with the Demo environment

Once we’ve downloaded the source code, we choose a folder in our server to put it, let’s say: c:/Temp/SampleApps.

Then, we open an IRIS session in a terminal, for example in MYOWNNAMESPACE, and run this code:

 do $system.OBJ.Load("c:/Temp/SampleApps/Synch/Config/Installer.cls","ck")
 set args("InstallingFromNS")="MYOWNNAMESPACE"
 set args("NamespaceMaster")="MYMASTERNODE"
 set args("NamespaceClient")="MYCLIENTNODE"
 do ##class(SampleApps.Synch.Config.Installer).setup(.args)

After execution, the demo environment will have been created for you and there will be(1):

• 2 new Namesapces: MYMASTERNODE and MYCLIENTNODE
• based also in 2 new databases: MYMASTERNODEDB and MYCLIENTNODEDB
• Both DB will be identical with already populated sample data
• 1 REST service for both new namespaces to have access to the APIs

And your environment will be ready for you to test.

(1) For the rest of the document, we will assume that the namespaces are MASTER and CLIENT.

REST Services

Just a bunch of REST services to make use and test this functionality. You can find them in SampleApps.Synch.API.v1.RestLegacyclass:

The common URL for both REST APIs are:

And the rest services themselves:

How synchronization feature works

You have a full explanation about this feature in InterSystems online documentation.

Some tips:

• if we want a solution to make use of this feature, we have to analize and decide in design time, as the classes which objects we want to synchronize will have to be defined accordingly.
• take into account that synchronization is asynchronous and bidirectional, that means, we decide when we do it, and it will require to build a SynchSet to bring data changes from MASTER to CLIENT and to build another SynchSet to bring data changes from CLIENT to MASTER.
• Metadata associated with synchronizations is stored in %SYNC.SyncTimetable.
• Data related to transactions of objects that we have decided to syncrhonize is stored internally in ^OBJ.JournalT(you don’t need to touch it).
• When we create a synchronization set (see %SYNC.SyncSet), all the synchset objects data is stored internally in ^OBJ.SYNC.<ssid>, where ssid is a unique identifier we have chosen.

How to test

Since the beginning, MASTER and CLIENT already have data and are identical. One easy and quick way to test will be adding some data to MASTER, prepare a synch set in MASTER to synchronize with CLIENT, and, finally, synchronize in CLIENT. Here it goes an example:

Example:
You can use whatever REST client, or directly from a terminal using methods in Sample.Synch.Utilclass. Below you have the curl commands (just in case you want to make use of REST services from command line). Of course you’ll have to change the commands to your authorization/IP/ports/DirPath needs

curl -X POST -H 'Authorization: Basic c3VwZXJ1c2VyOnN5cw==' -i http://localhost:52773/synchmaster/rest/v1/randomorder -
curl -X POST -H 'Authorization: Basic c3VwZXJ1c2VyOnN5cw==' -i http://localhost:52773/synchmaster/rest/v1/admin/prepsynch --data '{"syncID":3000,"dir":"c:/Temp","excludeNS":"CLIENT"}'
curl -X POST -H 'Authorization: Basic c3VwZXJ1c2VyOnN5cw==' -i http://localhost:52773/synchclient/rest/v1/admin/synchronize --data '{"syncID":3000,"dir":"c:/Temp","srcNS":"MASTER"}'

And there you go!… you just have synchronized data between 2 servers (well, 2 namespaces in this case). If you want to generate some conflicts, just modify the same object in both databases before synchronization. When trying to synchronize, it will detect that there was a modification in both sites over the same object and it will arise an event… who will win?? I’ll let you find out by yourself (Tip: look at Order class… :wink: )

End

I hope this code can help you in any way. And remember: What you code matters!

Enjoy!
Jose-Tomas Salvador