Query time mongoose occasionally taking 3-4 seconds - node.js

Question

I've written a back end node server for a multiplayer game I'm developing and most of the time each request takes about 20-100ms to resolve. However, sometimes (Maybe 1 out of 50 requests) I will do the same request and it will take 2000+ms to resolve.
The server is written entirely in node.js and is hosted on heroku. I am using mongoose to make the calls to the database.
Here is a screenshot of the logs, at the top you can see how queries normally function. The request comes in at 19:03:03.68 and the response is sent out at 19:03:03.73, saving all the data finishes at at 19:03:03.74. Heroku logs the request as taking 58ms which is the desired and expect outcome.
Below that is when the issue occurs. You can see multiple requests come in from two separate clients (Each client sends ~1 request per second which is correct) However the requests build up and after about 2000-5000ms they will all quickly resolve one after another. I’ve tried narrowing down the issue without much luck, but I believe it’s related to when I query the database as you can see multiple requests come in but the first query to the database doesn’t actually resolve until around 2300ms later. As far as I can tell these requests are identical to the ones that resolve in 20-100ms and occur completely at random.
The actual code is similar to this on the server (Simplified for the sake of this question):
console.log (“request received”);
Game.findOne({‘id’: gameID}, function(err, theGame){
console.log("First Query");
I also opened up the mongo shell for the database to look for queries taking an excessive amount of time (>2000ms) with this code:
db.system.profile.find( {millis: {$gt : 2000} } ).sort( { ts: 1} );
Here are the slightly modified results which should include everything relevant:
{ "op" : "update", "ns" : "theDb.players", "query" :
{ "_id" : ObjectId("572b8eb242d70903005df0df")
}, "updateobj" :
{ "$set" :
{ "lastSeen" : ISODate("2016-05-05T18:19:30.761Z"), "timeElapsed" : 16
}
}, "nscanned" : 1, "nscannedObjects" : 1, "nMatched" : 1, "nModified" : 1, "fastmod" : true, "keyUpdates" : 0, "writeConflicts" : 0, "numYield" : 0, "locks" :
{ "Global" :
{ "acquireCount":
{ "r" : NumberLong(2), "w" : NumberLong(2) }
}, "MMAPV1Journal" :
{ "acquireCount" :
{ "w" : NumberLong(2) }, "acquireWaitCount" :
{ "w" : NumberLong(1) }, "timeAcquiringMicros" :
{ "w" : NumberLong(7294179) }
}, "Database" :
{ "acquireCount" :
{ "w" : NumberLong(2) }
}, "Collection" :
{ "acquireCount" :
{ "W" : NumberLong(1) }
}, "oplog" :
{ "acquireCount" :
{ "w" : NumberLong(1) }
}
}, "milli" : 2298, "execStats" : {}, "ts" : ISODate("2016-05-05T18:19:33.060Z")
Second Result:
{ "op" : "update", "ns" : "theDb.connections", "query" :
{ "_id" : ObjectId("572b8eaf42d70903005df0dd")
}, "updateobj" :
{ "$set" :
{ "internalCounter" : 3, "lastCount" : 3, "lastSeen" : ISODate("2016-05-05T18:19:30.761Z"), "playerID" : 128863276517, "sinceLast" : 0
}
}, "nscanned" : 1, "nscannedObjects" : 1, "nMatched" : 1, "nModified" : 1, "keyUpdates" : 0, "writeConflicts" : 0, "numYield" : 0, "locks" :
{ "Global" :
{ "acquireCount" :
{ "r" : NumberLong(2), "w" : NumberLong(2)
}
}, "MMAPV1Journal" :
{ "acquireCount" :
{ "w" : NumberLong(2) }, "acquireWaitCount" :
{ "w" : NumberLong(1) }, "timeAcquiringMicros" :
{ "w" :NumberLong(7294149) }
}, "Database" :
{ "acquireCount" :
{ "w" : NumberLong(2) }
}, "Collection" :
{ "acquireCount" :
{ "W" : NumberLong(1) }
}, "oplog" :
{ "acquireCount" :
{ "w" : NumberLong(1) }
}
}, "millis" : 2299, "execStats" : {},"ts" : ISODate("2016-05-05T18:19:33.061Z")
I really need to ensure the latency for any request never exceeds 500ms otherwise it extremely irritating in the game itself. I’m really at a loss for what might be causing this and how to figure out more.
I'm assuming the cause for the issue is that timeAcquiringMicros is so long. I'm unsure of what is causing this though.
*Note, the client is requesting the data with just standard http requests, I’m not currently using any sockets.

Answer 1

Alright, I've finally solved the issue. The problem wasn't actually connected to anything that I had done. I was using the sandbox plan that mlab offers in connection to heroku which had my application competing for processing time with other people also using the sandbox plan. Their queries were slowing down the database causing those spikes in response times.
The solution: I had to upgrade to their shared cluster plan. Since upgrading I haven't had any irregularities in query times.