Mongo index issue I can't figure out

mongo_index_problem

I have a pretty complicated query. It looks like this - 

db.articles.find({"online_product_id": ObjectId("4e8910b27fd0dc66ef000006"), "draft": { "$ne":true }, "approval_status":"approved", "publish_time": { "$lte":ISODate("2013-10-24T16:45:35.000Z")}, "$or": [{"section":{"$in":["weekender"]}}, {"labels.identifier":{"$in":["weekender", "news local"]}}]}).sort({"publish_time":-1,"rank":1}).hint("article_lookup")

running that on my 2million record articles collection takes about 2 seconds. I added the following index:

{
		"v" : 1,
		"key" : {
			"online_product_id" : 1,
			"section" : 1,
			"labels.identifier" : 1,
			"draft" : 1,
			"approval_status" : 1,
			"publish_time" : -1
		},
		"ns" : "articlesite_development.articles",
		"name" : "article_lookup"
	}
	
	even with that index it's pretty slow but if i get rid of the sort and run this instead:
	
	db.articles.find({"online_product_id": ObjectId("4e8910b27fd0dc66ef000006"), "draft": { "$ne":true }, "approval_status":"approved", "publish_time": { "$lte":ISODate("2013-10-24T16:45:35.000Z")}, "$or": [{"section":{"$in":["weekender"]}}, {"labels.identifier":{"$in":["weekender", "news local"]}}]}).hint("article_lookup")
	
	it's really fast < 300ms. 
	
If i get rid of the second clause of the $OR but leave the sort and instead run this: 

	db.articles.find({"online_product_id": ObjectId("4e8910b27fd0dc66ef000006"), "draft": { "$ne":true }, "approval_status":"approved", "publish_time": { "$lte":ISODate("2013-10-24T16:45:35.000Z")}, "$or": [{"section":{"$in":["weekender"]}}]}).hint("article_lookup")
	
It's also really fast. Same results if i switch which clause of the or i include and put back the labels.identifier but eliminate the section. 

So 2 questions. 

1) Why does the sort break my index?
2) If you noticed I'm explicitley using hint() in the queries. That's because without it mongo doesn't use the right index for the query. Any idea why it's not picking the right index?



Thanks to anyone who sees this!




EDIT: Posting explains for the slow query and one of the quicker ones. 

EXPLAIN FOR - db.articles.find({"online_product_id": ObjectId("4e8910b27fd0dc66ef000006"), "draft": { "$ne":true }, "approval_status":"approved", "publish_time": { "$lte":ISODate("2013-10-24T16:45:35.000Z")}, "$or": [{"section":{"$in":["weekender"]}}, {"labels.identifier":{"$in":["weekender", "news local"]}}]}).sort({"publish_time":-1,"rank":1}).hint("article_lookup")

{
	"cursor" : "BtreeCursor article_lookup multi",
	"isMultiKey" : true,
	"n" : 254,
	"nscannedObjects" : 195182,
	"nscanned" : 195188,
	"nscannedObjectsAllPlans" : 195182,
	"nscannedAllPlans" : 195188,
	"scanAndOrder" : true,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 1682,
	"indexBounds" : {
		"online_product_id" : [
			[
				ObjectId("4e8910b27fd0dc66ef000006"),
				ObjectId("4e8910b27fd0dc66ef000006")
			]
		],
		"section" : [
			[
				{
					"$minElement" : 1
				},
				{
					"$maxElement" : 1
				}
			]
		],
		"labels.identifier" : [
			[
				{
					"$minElement" : 1
				},
				{
					"$maxElement" : 1
				}
			]
		],
		"draft" : [
			[
				{
					"$minElement" : 1
				},
				true
			],
			[
				true,
				{
					"$maxElement" : 1
				}
			]
		],
		"approval_status" : [
			[
				"approved",
				"approved"
			]
		],
		"publish_time" : [
			[
				ISODate("2013-10-24T16:45:35Z"),
				true
			]
		]
	},
	"server" : "Joshs-MacBook-Pro.local:27017"
}



EXPLAIN FOR - db.articles.find({"online_product_id": ObjectId("4e8910b27fd0dc66ef000006"), "draft": { "$ne":true }, "approval_status":"approved", "publish_time": { "$lte":ISODate("2013-10-24T16:45:35.000Z")}, "$or": [{"section":{"$in":["weekender"]}}]}).hint("article_lookup")




{
	"clauses" : [
		{
			"cursor" : "BtreeCursor article_lookup multi",
			"isMultiKey" : true,
			"n" : 251,
			"nscannedObjects" : 265,
			"nscanned" : 265,
			"nscannedObjectsAllPlans" : 265,
			"nscannedAllPlans" : 265,
			"scanAndOrder" : false,
			"indexOnly" : false,
			"nYields" : 0,
			"nChunkSkips" : 0,
			"millis" : 3,
			"indexBounds" : {
				"online_product_id" : [
					[
						ObjectId("4e8910b27fd0dc66ef000006"),
						ObjectId("4e8910b27fd0dc66ef000006")
					]
				],
				"section" : [
					[
						"weekender",
						"weekender"
					]
				],
				"labels.identifier" : [
					[
						{
							"$minElement" : 1
						},
						{
							"$maxElement" : 1
						}
					]
				],
				"draft" : [
					[
						{
							"$minElement" : 1
						},
						true
					],
					[
						true,
						{
							"$maxElement" : 1
						}
					]
				],
				"approval_status" : [
					[
						"approved",
						"approved"
					]
				],
				"publish_time" : [
					[
						ISODate("2013-10-24T16:45:35Z"),
						true
					]
				]
			}
		},
		{
			"cursor" : "BtreeCursor article_lookup multi",
			"isMultiKey" : true,
			"n" : 3,
			"nscannedObjects" : 4,
			"nscanned" : 50,
			"nscannedObjectsAllPlans" : 4,
			"nscannedAllPlans" : 50,
			"scanAndOrder" : false,
			"indexOnly" : false,
			"nYields" : 0,
			"nChunkSkips" : 0,
			"millis" : 0,
			"indexBounds" : {
				"online_product_id" : [
					[
						ObjectId("4e8910b27fd0dc66ef000006"),
						ObjectId("4e8910b27fd0dc66ef000006")
					]
				],
				"section" : [
					[
						{
							"$minElement" : 1
						},
						{
							"$maxElement" : 1
						}
					]
				],
				"labels.identifier" : [
					[
						"news local",
						"news local"
					],
					[
						"weekender",
						"weekender"
					]
				],
				"draft" : [
					[
						{
							"$minElement" : 1
						},
						true
					],
					[
						true,
						{
							"$maxElement" : 1
						}
					]
				],
				"approval_status" : [
					[
						"approved",
						"approved"
					]
				],
				"publish_time" : [
					[
						ISODate("2013-10-24T16:45:35Z"),
						true
					]
				]
			}
		}
	],
	"n" : 254,
	"nscannedObjects" : 269,
	"nscanned" : 315,
	"nscannedObjectsAllPlans" : 269,
	"nscannedAllPlans" : 315,
	"millis" : 4,
	"server" : "Joshs-MacBook-Pro.local:27017"
}


I also forgot that I tried it with one or clause removed and the sort added back in, that was fast. 

db.articles.find({"online_product_id": ObjectId("4e8910b27fd0dc66ef000006"), "draft": { "$ne":true }, "approval_status":"approved", "publish_time": { "$lte":ISODate("2013-10-24T16:45:35.000Z")}, "$or": [{"section":{"$in":["weekender"]}}]}).sort({"publish_time":-1,"rank":1}).hint("article_lookup").explain()
{
	"cursor" : "BtreeCursor article_lookup multi",
	"isMultiKey" : true,
	"n" : 251,
	"nscannedObjects" : 265,
	"nscanned" : 265,
	"nscannedObjectsAllPlans" : 265,
	"nscannedAllPlans" : 265,
	"scanAndOrder" : true,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 7,
	"indexBounds" : {
		"online_product_id" : [
			[
				ObjectId("4e8910b27fd0dc66ef000006"),
				ObjectId("4e8910b27fd0dc66ef000006")
			]
		],
		"section" : [
			[
				"weekender",
				"weekender"
			]
		],
		"labels.identifier" : [
			[
				{
					"$minElement" : 1
				},
				{
					"$maxElement" : 1
				}
			]
		],
		"draft" : [
			[
				{
					"$minElement" : 1
				},
				true
			],
			[
				true,
				{
					"$maxElement" : 1
				}
			]
		],
		"approval_status" : [
			[
				"approved",
				"approved"
			]
		],
		"publish_time" : [
			[
				ISODate("2013-10-24T16:45:35Z"),
				true
			]
		]
	},
	"server" : "Joshs-MacBook-Pro.local:27017"
}

bummer. thanks for the help though. i'll try looking at 2 indexes and if that doesn't work i'll investigate a migration.