Databases
StackOverflow2013
Postsdbo
POSlow (high latency) upon queries with sort mongoDB
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POSlow (high latency) upon queries with sort mongoDB
    primarykey
    data
    text
    <p>I am currently migrating from couchdb to mongodb, still learning this stuff and have a problem anytime I do some queries with sorting in my webpage. I am using codeigniter as the framework and using <a href="https://github.com/alexbilbie/codeigniter-mongodb-library/tree/v2" rel="nofollow">alexbilbie</a> lib for mongodb php library.</p> <p>So, here is my problem: I intend to do queries from sensors in a room that updated each second (thus, already saved thousands docs in collection) and to get each latest sensor value I use this query from model:</p> <pre><code>function mongoGetDocLatestDoc($sensorid){ $doc = $this-&gt;mongo_db-&gt;where(array('SensorId'=&gt;$sensorid))-&gt;limit(1)-&gt;order_by(array('_id'=&gt;'DESC'))-&gt;get('my_mongo'); return $doc; } </code></pre> <p>if I called this with my controller, it took a lot of time to process the query and even worse if I change the sort by timestamp. and it is double the latency each time I called this again for the second sensor, let alone I have more than 10 sensors that need this query in the same page. Am I doing it wrong or there is some more efficient way to get the latest data from collection?</p> <p>edit: @Sammaye : I tried making an index based on your suggestion and here is the explain generated after I executed the query:</p> <pre><code>"cursor" : "BtreeCursor timestamp_desc", "nscanned" : 326678, "nscannedObjects" : 326678, "n" : 50, "millis" : 4402, "nYields" : 7, "nChunkSkips" : 0, "isMultiKey" : false, "indexOnly" : false, "indexBounds" : { "timestamp" : [ [ { "$maxElement" : 1 }, { "$minElement" : 1 } ] ] } </code></pre> <p>as per comparison, this explain the first query without using index (that executed faster) :</p> <pre><code>"cursor" : "BasicCursor", "nscanned" : 385517, "nscannedObjects" : 385517, "n" : 50, "millis" : 1138, "nYields" : 0, "nChunkSkips" : 0, "isMultiKey" : false, "indexOnly" : false, "indexBounds" : { } </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USZuzu Softman
    1. USZuzu Softman
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. COWhat does the indexes look like?
      singulars
      1. POSlow (high latency) upon queries with sort mongoDB
      1. USSammaye
    2. COforgive me for my lack of knowledge. but my index only based on default provided by mongodb. which is by {"_id":1} maybe this explains why it took time to sort it using timestamp since it has not indexed yet. but still even using _id to sort, I could not have a satisfying time latency.
      singulars
      1. POSlow (high latency) upon queries with sort mongoDB
      1. USZuzu Softman
    3. COYou will to add compound index on sensorid and _id to make this efficient. The index would look like {"sensorid": 1, "_id": -1}, which is first sensorid ascending order and _id decending order. See the following page for docs on compound indexes in MongoDB: http://docs.mongodb.org/manual/core/indexes/#compound-indexes
      singulars
      1. POSlow (high latency) upon queries with sort mongoDB
      1. USJames Wahlin
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload