GT.M can not be re-opened

[dlwicksell]

GT.M can not be re-opened

[dlwicksell]

That is the expected behavior. Nodem relies upon the GT.M Call-in interface, which allows a process to open the database one time, and once it has closed its database connection, that process is no longer allowed to open it. So you should only open the connection to GT.M one time in any Node.js process, and you should only close the connection to GT.M one time in any Node.js process, unless you are finished accessing it in that process.

The initialization is what adds Nodem into your Node.js process. And that is something you only need to do one time as well. Initializing Nodem creates the appropriate Nodem object that gives you access to Nodem, using a constructor method which wraps a C++ class which exposes the various Nodem methods. If you require a module more than once, Node.js will only add that module to that process's image one time.

So you only need to require Nodem one time per process, and you only need to initialize Nodem one time per process, and you only need to open the database connection one time per process, and you should only close the connection to the database after you are done talking to GT.M, as you cannot close it and then re-open it in the same process, which is a limitation in the Call-in API of GT.M. Actually you don't even need to close the database connection, because all of its resources will be released whenever a process that is linked with GT.M ends anyway.

You should therefore not try requiring, initializing, opening, or closing the Nodem interface for each function or method in your Node.js code. I hope that helps.

[wpoosanguansit]

As this is quite unusual from the normal practice with other db, I hope you do not mind I rehash it a bit. So the pattern found in the example is only for short term process. And for long running processes, we just need to open the connection, init but do not care to close it as it will be garbage collected if and when the process is terminated. And there is no memory leak as a result of not closing the db. Is my understanding correct? Thanks of your help.

[dlwicksell]

Yes, that is basically correct. When the process is terminated, its resources will be cleaned up and not leaked. That is actually a function of the operating system. When a process dies, its virtual address space is removed and any physical memory mapped to it is freed. In addition, Nodem is using V8 C++ APIs, which themselves allocate memory that is cleaned up by a garbage collector (the JavaScript garbage collector in Node.js). And when I have to allocate dynamic memory on the heap in C code, to work with GT.M, I am careful (I believe) to deallocate it properly.

But, closing the database connection will ensure that the terminal is reset to the settings it had before it opened a connection to GT.M (which changes those settings in surprising ways), as well as explicitly allowing GT.M the chance to clean up its resources. I'd still advise that you use the close API in your code. Again, only close the database connection when you no longer need to access GT.M in that process.

[dlwicksell]

For long-running Node.js processes, you should probably close the database in the handler code for stopping the Node process. E.g.

process.on('exit', function() { 
    db.close(); 
});

and

process.on('SIGINT', function() {
    db.close();
});

Where you can put your own cleanup code right before or after closing the connection to GT.M.