Optimizing MongoDB Compound Indexes

http://emptysquare.net/blog/optimizing-mongodb-compound-indexes/

by jiryu • 14 years ago

46 11 14 years ago

MartinMond2• 14 years ago

Is MongoDB actually able to combine 2 or more indices?

jiryu• 14 years ago

No - it can only use one for a given query. But a compound index like the ones I describe in the post can index many fields.

MartinMond2• 14 years ago

Yes of course, but it's kinda slow if you have to maintain one compound index for each possible query you're going to run, that's why I was asking.

mattparlane2• 14 years ago

You may be interested in this:

https://jira.mongodb.org/browse/SERVER-3071

It's index intersection, and it's scheduled for 2.3.1 which is the next next dev release. I'm hoping it makes it in for 2.4.

dkhenry2• 14 years ago

What should be added to this is the ability to tell Mongo to return an error if your query requires a table scan. That one configuration item can be the difference between a request returning an error and a whole site going down for an extended period.

lucian1900• 14 years ago

You can ask it to explain what it did, just like you'd ask for the last error. Then in your app enforce whatever rules related to indexes you wish.

mattparlane2• 14 years ago

explain actually runs the query. From http://www.mongodb.org/display/DOCS/Explain :

    Note that explain runs the actual query to determine the result. If the query is slow, the explain will be slow too.

pbrumm• 14 years ago

There is a config setting for that

  notablescan = true

http://docs.mongodb.org/manual/reference/configuration-optio...

dkhenry2• 14 years ago

Right I was saying that the author should add that to his article. Its a very valuable configuration item and anytime your dealing with optimizing indexes its worth enabling.

Loic• 14 years ago

About 2 years ago (time is flying) I explained how I did the same to support range queries over "n" attributes, the method ended up being in the book "MongoDB, the Definitive Guide" by Chodorow and Dirolf (O'Reilly):

http://chemeo.com/doc/technology

(Search for "Indexing For High Speed Search" to skip non MongoDB related information).

Optimizing MongoDB Compound Indexes

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