CODEWITHSUNDEEP
javascriptmongodb
mpenkov
mpenkov

Reputation: 21906

Why is this MongoDB loop executing more times than expected?

I have this server-side JS script:

// Run processNames on all rows in cities
var cur = db.cities.find();
cur.immortal = true;
var j = 0;
var total = cur.count();
cur.forEach(function(obj) {
    processNames(obj);
    if (j % 100000 === 0) {
        print(j + "/" + total + " cities processed");
    }
    j++;
});
print("Completed load: " + j + " cities processed");

In the output, I see this:

...
4800000/3411205 cities processed
4900000/3411205 cities processed
5000000/3411205 cities processed
5100000/3411205 cities processed
5200000/3411205 cities processed
5300000/3411205 cities processed
5400000/3411205 cities processed
5500000/3411205 cities processed

How can this be happening? The cursor returns only 3411205 documents, but the forEach loop is executing over 5 million times. What's going on?

Upvotes: 1

Views: 82

Answers (1)

study
study

Reputation: 5817

I think you modify documents in processNames() method which causes MongoDB to relocate documents. You can use snapshot() to overcome this problem.

var cur = db.cities.find().snapshot();

Upvotes: 1

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