What the meaning of lazy-load when calling the perl find() function for mongoDB?

Question

I use perl script as a client to query mongoDB databases.my code is as below:

my $some_users = $users->find({"name" => "Joe"});
 while (my $doc = $all_users->next) {
        print $doc->{'name'}."\n";
    }

cpan tutorial says:

find returns a MongoDB::Cursor, which can be iterated over. It lazily loads results from the database.

And yes, after my careful observation，I find that it takes a very short time when calling the find() , instead, the iteration of MongoDB::Cursor will take a long time if the find() function returns many data.So ,I becomes very confused,what does it mean by lazy load?Lazy load means "do nothing" ?lazy load means cheating?

It's only cheating if you get caught.

friedo
– friedo

2013-10-08 15:36:26 +00:00
Commented Oct 8, 2013 at 15:36 — friedo
– friedo, Commented Oct 8, 2013 at 15:36

friedo · Accepted Answer · 2013-10-08 15:29:39Z

1

Lazy load means returning an iterator instead of whole data.

So in your loop :

This does not return and store full data in $some_users, only a reference/iterator to the data matching the query.

    my $some_users = $users->find({"name" => "Joe"});

Now you can iterate over that data using the iterator, the records are fetched by the Perl Mongodb driver in the loop, it may fetch them one by one, or prefetch a batch of say 1000 records,and then refetch after 1000, that depends on the driver implementation.

     while (my $doc = $all_users->next) {
            print $doc->{'name'}."\n";
        }

edited Oct 8, 2013 at 15:29

friedo

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answered Oct 8, 2013 at 13:33

DhruvPathak

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