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MongoDB: How to deal with big collection

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Recently, I am involved in a project where I have a collection of posts (comments). In this collection, I have around 20 millions posts where each document contains some information about each post (id, URL, content, author, likes, dislikes).

Yesterday, I tried to identify the number of posts per user meaning that as a result I would like to have the list of author with their number of posts.

To this end, I have used a simple java code... After around 10 hours, I got the result of only 180 users whereas I have more than 500 000 users in my collection. So, using my code I will need months :)

Please can you recommend me some tips to improve the efficiently of my queries.

posted Mar 16, 2016 by anonymous

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1 Answer

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you are provide some more information about your current schema and the Java code you have written?
Can you also tell if you have indexes, and if so what are they?

My first guess would be that you are looping over the complete collection in code instead of using a query / aggregation.
Maybe you would need to adjust your model to your query if this is needed/possible.

Also,

this is an example of what might work for you :

db.comments.aggregate([ {$group: {_id:"$author",total:{$sum:1}}},{ $sort: { total: -1 } } ])

The sort is optional and if you could, you should do a match first to make you working set smaller.

answer Apr 6, 2016 by Manikandan J
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