MongoDB : query result size greater than collection size

Question

I'm analyzing a MongoDB data source to check its quality. I'm wondering if every document contains the attribute time: so I used this two command

> db.droppay.find().count();  
291822   
> db.droppay.find({time: {$exists : true}}).count()   
293525

How can I have more elements with a given field than the elements contained in whole collection ? What's going wrong ? I'm unable to find the mistake. If it's necessary I can post you the expected structure of the document.

Mongo Shell version is 1.8.3. Mongo Db version is 1.8.3.

Thanks in advance

---

This is the expected structure of the document entry:

{
  "_id" : ObjectId("4e6729cc96babe974c710611"), 
  "action" : "send",
  "event" : "sent",
  "job_id" : "50a1b7ac-7482-4ad6-ba7d-853249d6a123",    
  "result_code" : "0",
  "sender" : "",
  "service" : "webcontents",
  "service_name" : "webcontents",
  "tariff" : "0",
  "time" : "2011-09-07 10:22:35",
  "timestamp" : "1315383755",
  "trace_id" : "372",
  "ts" : "2011-09-07 09:28:42"
}

Answer 1

My guess is that is an issue with the index. I bet that droppay has an index on :time, and some unsafe operation updated the underlying collection without updating the index.

Can you try repairing the db, and see if that makes it better.

Good luck.