考虑以下查询，这是一个相当简单的用例：
db.Transactions.find({
$or: [
{ "from.addresses" : "name@domain.com" },
{ "to.addresses" : "name@domain.com" }
]
}).sort({ "time" : -1 });
“from.addresses”和“to.addresses”是索引字段（数组）。那些指数不是复合的。目前没有关于“时间”的索引。 请注意，我在此集合上使用分片，这可能会影响查询的行为。
问题是：
是否可以使MongoDB使用索引？ 我目前正在考虑运行2个单独的查询（$或每一个一个）并自己合并（比$或行为更快）。
请在下面找到完整的.explain（）（在比真实的小集合上运行，在真正的集合上运行需要几个小时）：
{
"clusteredType" : "ParallelSort",
"shards" : {
"rs/mongo-a:27017,mongo-b:27017" : [
{
"cursor" : "BasicCursor",
"isMultiKey" : false,
"n" : 1356,
"nscannedObjects" : 45589,
"nscanned" : 45589,
"nscannedObjectsAllPlans" : 45589,
"nscannedAllPlans" : 45589,
"scanAndOrder" : true,
"indexOnly" : false,
"nYields" : 356,
"nChunkSkips" : 8014,
"millis" : 44726,
"indexBounds" : {
},
"server" : "mongo-a:27017"
}
],
"rs1/mongo-a1:27018,mongo-b1:27018" : [
{
"cursor" : "BasicCursor",
"isMultiKey" : false,
"n" : 3435,
"nscannedObjects" : 15663,
"nscanned" : 15663,
"nscannedObjectsAllPlans" : 15663,
"nscannedAllPlans" : 15663,
"scanAndOrder" : true,
"indexOnly" : false,
"nYields" : 4,
"nChunkSkips" : 0,
"millis" : 505,
"indexBounds" : {
},
"server" : "mongo-a1:27018"
}
],
"rs2/mongo-a2:27018,mongo-b2:27018" : [
{
"cursor" : "BasicCursor",
"isMultiKey" : false,
"n" : 2208,
"nscannedObjects" : 10489,
"nscanned" : 10489,
"nscannedObjectsAllPlans" : 10489,
"nscannedAllPlans" : 10489,
"scanAndOrder" : true,
"indexOnly" : false,
"nYields" : 2,
"nChunkSkips" : 0,
"millis" : 329,
"indexBounds" : {
},
"server" : "mongo-a2:27018"
}
],
"rs3/mongo-a3:27018,mongo-b3:27018" : [
{
"cursor" : "BasicCursor",
"isMultiKey" : false,
"n" : 2249,
"nscannedObjects" : 10500,
"nscanned" : 10500,
"nscannedObjectsAllPlans" : 10500,
"nscannedAllPlans" : 10500,
"scanAndOrder" : true,
"indexOnly" : false,
"nYields" : 7,
"nChunkSkips" : 0,
"millis" : 439,
"indexBounds" : {
},
"server" : "mongo-a3:27018"
}
],
"rs4/mongo-a4:27018,mongo-b4:27018" : [
{
"cursor" : "BasicCursor",
"isMultiKey" : false,
"n" : 2251,
"nscannedObjects" : 10488,
"nscanned" : 10488,
"nscannedObjectsAllPlans" : 10488,
"nscannedAllPlans" : 10488,
"scanAndOrder" : true,
"indexOnly" : false,
"nYields" : 4,
"nChunkSkips" : 0,
"millis" : 336,
"indexBounds" : {
},
"server" : "mongo-a4:27018"
}
],
"rs5/mongo-a5:27018,mongo-b5:27018" : [
{
"cursor" : "BasicCursor",
"isMultiKey" : false,
"n" : 1175,
"nscannedObjects" : 5220,
"nscanned" : 5220,
"nscannedObjectsAllPlans" : 5220,
"nscannedAllPlans" : 5220,
"scanAndOrder" : true,
"indexOnly" : false,
"nYields" : 2,
"nChunkSkips" : 0,
"millis" : 376,
"indexBounds" : {
},
"server" : "mongo-a5:27018"
}
]
},
"cursor" : "BasicCursor",
"n" : 12674,
"nChunkSkips" : 8014,
"nYields" : 375,
"nscanned" : 97949,
"nscannedAllPlans" : 97949,
"nscannedObjects" : 97949,
"nscannedObjectsAllPlans" : 97949,
"millisShardTotal" : 46711,
"millisShardAvg" : 7785,
"numQueries" : 6,
"numShards" : 6,
"millis" : 44939
}