php mongodb optimization sort query

Question

i need to find the most recent element, the field "data_caricamento" save the date. so i made a index with MognoDb shell:

db.collection.ensureIndex({"data_caricamento": -1})

and with the php code below i have what i need

$cursor=$collection->find();
    $cursor->sort(array("data_caricamento"=> -1));
    $cursor->limit($n);

but i think that should be a better way to do it, for example there is a way to query the directly the index? thx.

Sammaye · Accepted Answer · 2014-05-08 09:57:35Z

1

there is a way to query the directly the index?

Sort of. You can do a covered query here by doing:

$cursor = $collection
    ->find(array(), array('_id' => 0, 'data_caricamento' => 1))
    ->sort(array("data_caricamento" => -1))
    ->limit($n);

That will query only the index.

answered May 8, 2014 at 9:57

Sammaye

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4 Comments

user3535936 Over a year ago

but still sort even if the index is yet sorted. so the complexity not changed

Sammaye Over a year ago

@user3535936 wehat do you mean? The index is already sorted, your just reading from the place in the index

user3535936 Over a year ago

but on your code still have 3 command on the pipe find->sort->limit so i ask myself if it will improve performance

Sammaye Over a year ago

@user3535936 yes all I have done is added projection to let MongoDB know what it needs to pick out allowing it to say: "I don't need to look at the records to know what to pick"

Sarthak Sawhney · Accepted Answer · 2014-05-13 04:02:47Z

0

Try using the hint. And if you want to check whether the indexes got used by your query use explain().

....
$collection->find()->sort(array('data_caricamento'=>1))->hint(array('data_caricamento'=>1));
print_r($cursor->explain());

This will help you see that your queries are hitting index for faster search and sorting! Cheers!

answered May 13, 2014 at 4:02

Sarthak Sawhney

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