Mongoose limit/offset and count query

Question

Bit of an odd one on query performance... I need to run a query which does a total count of documents, and can also return a result set that can be limited and offset.

So, I have 57 documents in total, and the user wants 10 documents offset by 20.

I can think of 2 ways of doing this, first is query for all 57 documents (returned as an array), then using array.slice return the documents they want. The second option is to run 2 queries, the first one using mongo's native 'count' method, then run a second query using mongo's native $limit and $skip aggregators.

Which do you think would scale better? Doing it all in one query, or running two separate ones?

Edit:

// 1 query var limit = 10; var offset = 20;  Animals.find({}, function (err, animals) {     if (err) {         return next(err);     }      res.send({count: animals.length, animals: animals.slice(offset, limit + offset)}); });   // 2 queries Animals.find({}, {limit:10, skip:20} function (err, animals) {                 if (err) {         return next(err);     }      Animals.count({}, function (err, count) {         if (err) {             return next(err);         }          res.send({count: count, animals: animals});     }); }); 

Answer 1

I suggest you to use 2 queries:

1. db.collection.count() will return total number of items. This value is stored somewhere in Mongo and it is not calculated.

2. db.collection.find().skip(20).limit(10) here I assume you could use a sort by some field, so do not forget to add an index on this field. This query will be fast too.

I think that you shouldn't query all items and than perform skip and take, cause later when you have big data you will have problems with data transferring and processing.