Datastore solution for tag search

Question

I\'ve got millions of items ordered by a precomputed score. Each item has many boolean attributes. Let says that there is about ten thousand possible attributes totally, each

Answer 1

Mongodb can handle what you want, if you stored your objects like this

{ score:2131, attributes: ["attr1", "attr2", "attr3"], ... }

Then the following query will match all the items that have att1 and attr2

c = db.mycol.find({ attributes: { $all: [ "attr1", "attr2" ] } })

but this won't match it

c = db.mycol.find({ attributes: { $all: [ "attr1", "attr4" ] } })

the query returns a cursor, if you want this cursor to be sorted, then just add the sort parameters to the query like so

c = db.mycol.find({ attributes: { $all: [ "attr1", "attr2" ] }}).sort({score:1})

Have a look at Advanced Queries to see what's possible.

Appropriate indexes can be setup as follows

db.mycol.ensureIndex({attributes:1, score:1})

And you can get performance information using

db.mycol.find({ attributes: { $all: [ "attr1" ] }}).explain()

Mongo explains how many objects were scanned, how long the operation took and various other statistics.