Question

In my app (node / express / redis), I use some code to update several items in DB at the same time:

app.put('myaction', function(req, res){
    // delete stuff
    db.del("key1");
    db.srem("set1", "test");

    // Add stuff
    db.sadd("set2", "test2");
    db.sadd("set3", "test3");
    db.hmset("hash1", "k11", "v11", "k21", "v21");
    db.hmset("hash2", "k12", "v12", "k22", "v22");
    // ...

    // Send response back
    res.writeHead(200, {'content-type': 'application/json'});
    res.write(JSON.stringify({ "status" : "ok" }));

    res.end(); 
});

Can I be sure ALL those actions will be performed before the method returns ? My concern is the asynchronous processing. As I do not use callback function in the db actions, will this be alright ?

Answer 1

Use the MULTI/EXEC command to create a queue of your commands and execute them in a row. Then use a callback to send a coherent response back (success/failure).
Note that you must use Redis’ AOF to avoid that – in case of crash – the db state is not coherent with your logic because only a part of the commands in the queue were executed: i.e. MULTI/EXEC is not transactional upon execution. This is a useful reference.