MongoDB indexes and the $or operator
Sorry if this has been asked before. I couldn't find a definitive answer. Can I query on a mongodb index if my query contains the $or operator? My query looks something like this:
// find everything in the collection
$cursor = $collection->find(array(
'$or' => array(
array('album_id' => array(
'$in' => $this->my_album_ids
),
'type' => array(
'$in' => array('like','comment')
)
),
array(
'user_id' => (int)session_item('user_id'),
'type' => 'message',
'reply' => 'no'
)
),
'timestamp' => array('$gt' => (int)$since)))->sort(array('timestamp'=>-1))->skip($start)->limit($amount);
The Example is in PHP, but I guess this is applicable to any language.
Update:
The following are my indexes, but the above query does not use them. It looks right to me though.
$collection->ensureIndex(array(
'album_id' => 1,
'type' => 1,
'timestamp' => -1,
));
$collection->ensureIndex(array(
'user_id' => 1,
'type' => 1,
'reply' => 1,
'timestamp' => -1,
));
Here is my explain()
Array
(
[cursor] => BasicCursor
[nscanned] => 12
[nscannedObjects] => 12
[n] => 6
[scanAndOrder] => 1
[millis] => 0
[nYields] => 0
[nChunkSkips] => 0
[isMultiKey] =>
[ind开发者_Python百科exOnly] =>
[indexBounds] => Array
(
)
[allPlans] => Array
(
[0] => Array
(
[cursor] => BasicCursor
[indexBounds] => Array
(
)
)
)
[oldPlan] => Array
(
[cursor] => BasicCursor
[indexBounds] => Array
(
)
)
)
Yes, an $or query will use indexes as appropriate. For example :
> db.test.ensureIndex({a:1})
> db.test.ensureIndex({b:1})
> db.test.find({$or:[{a:1}, {b:2}]}).explain()
{
"clauses" : [
{
"cursor" : "BtreeCursor a_1",
"nscanned" : 0,
"nscannedObjects" : 0,
"n" : 0,
"millis" : 0,
"nYields" : 0,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
"a" : [
[
1,
1
]
]
}
},
{
"cursor" : "BtreeCursor b_1",
"nscanned" : 0,
"nscannedObjects" : 0,
"n" : 0,
"millis" : 1,
"nYields" : 0,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
"b" : [
[
2,
2
]
]
}
}
],
"nscanned" : 0,
"nscannedObjects" : 0,
"n" : 0,
"millis" : 1
}
Mongo use no IndexBounds on an sorted OR Query. Try
db.test.find({$or:[{a:1}, {b:2}]}).sort(somesort).explain();
and IndexBounds use with $minElement
and $maxElement
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