Home/ Questions/Q 1108217
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-17T02:02:56+00:00

I’m thinking about trying MongoDB to use for storing our stats but have some

  • 0

I’m thinking about trying MongoDB to use for storing our stats but have some general questions about whether I’m understanding it correctly before I actually start learning it.

I understand the concept of using documents, what I’m not too clear about is how much data can be stored inside each document. The following diagram explains the layout I’m thinking of:

Website (document)
 - some keys/values about the particular document
 - statistics (tree)
   - millions of rows where each record is inserted from a pageview (key/value array containing data such as timestamp, ip, browser, etc)

What got me excited about mongodb was the grouping functions such as:
http://www.mongodb.org/display/DOCS/Aggregation

db.test.group(
{ cond: {"invoked_at.d": {$gte: "2009-11", $lt: "2009-12"}}
, key: {http_action: true}
, initial: {count: 0, total_time:0}
, reduce: function(doc, out){ out.count++; out.total_time+=doc.response_time }
, finalize: function(out){ out.avg_time = out.total_time / out.count }
} );

But my main concern is how hard would that command for example be on the server if there is say 10’s of millions of records across dozens of documents on a 512-1gb ram server on rackspace for example? Would it still run low load?

Is there any limit to the number of documents MongoDB can have (seperate databases)? Also, is there any limit to the number of records in a tree I explained above? Also, does that query I showed above run instantly or is it some sort of map/reduce query? Not very sure if I can execute that upon page load in our control panel to get those stats instantly.

Thanks!

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Every document has a size limit of 4MB (which in text is A LOT).

    It’s recommended to run MongoDB in replication mode or to use sharding as you otherwise will have problems with single-server durability. Single-server durability is not given because MongoDB only fsync’s to the disk every 60 seconds, so if your server goes down between two fsync’s the data that got inserted/updated in that time will be lost.

    There is no limit of documents other than your disk space in mongodb.

    You should try to import a dataset that matches your data (or generate some test data) to MongoDB and analyse how fast your query executes. Remember to set indexes on those fields that you use heavily in your queries. Your above query should work pretty well even with a lot of data.

    In order to analyze the speed of your query use the database profiler MongoDB comes with. On the mongo shell do:

    db.setProfilingLevel(2); // to set the profiling level
[your query]
db.system.profile.find(); // to see the results

    Remember to turn off profiling once you’re finished (log will get pretty huge otherwise).

    Regarding your database layout I suggest to change the “schema” (yeah yeah, schema less..) to:

    website (collection):
    – some keys/values about the particular document

    statistics (collection)
    – millions of rows where each record is inserted from a pageview (key/value array containing data such as timestamp, ip, browser, etc)
    + DBRef to website

    See Database References

    • 0