Question

I have a node app with mongo server on an amazon ec2 instance. It works great, but I just added a new API call and every time I call it, the server freezes and I cannot access/ssh into it for several hours. While this is happening, my server goes down which makes the app that relies on it unusable and my users angry…

This code works perfectly on my localhost, but as soon as I run it on my server it freezes. My thoughts are that it may be crashing mongo? I have no idea why this would happen…

If anyone has any ideas what could be going wrong, please let me know.

node is using express. The send_error function will perform a res.send({some error}). db.CommentModel returns mongoose.model(‘comment’, Comment);

in app.js

app.get('/puzzle/comment/:id', auth.restrict, puzzle.getComments);

in the file which defines getComments

exports.getComments = function(req, res)
{   
    var userID = _u.stripNonAlphaNum(req.params.id);

    var CommentModel = db.CommentModel;
    CommentModel.find({user: userID}, function(e, comments) {
        if(e) 
        {
            err.send_error(err.DB_ERROR, res);
        }
        else if (!comments)
        {
            err.send_error(err.DB_ERROR, res);
        }
        else if (comments.length == 0)
        {
            res.send([]);
    }
    else
    {
        var commentIDs = [];
        for (var i = 0; i<comments.length; i++)
        {
            commentIDs.push({_id: comments[i].puzzle});
        }
        var TargetModel = pApp.findPuzzleModel(_u.stripNonAlphaNum(req.apiKey));
            TargetModel.find({removed: false, $or: commentIDs}, function(e, puzzles) {
                if(e) 
                {
                    err.send_error(err.DB_ERROR, res);
                }
                else if (!puzzles)
                {
                    err.send_error(err.DB_ERROR, res);
                }
                else
                {
                    res.send(puzzles);
                }
            });
        }
    });
}

Answer 1

It sounds like your query is causing something on your server (potentially mongo) to consume a very large amount of CPU – as this is commonly what causes the issue you have seen with SSH access.

You should try reading over the logs of your mongo instance and seeing if there are any long running queries.

Monngodb provides an internal profiler for examining long running commands. Try setting long running profiling level to 1, running the command and examining the logfile output.

More details on the profiler are available at http://www.mongodb.org/display/DOCS/Database+Profiler