我有一個基於組合索引構建的查詢,並且我已經從mongo shell驗證此查詢可以作爲僅索引查詢運行。無法使用mongoid執行覆蓋(indexOnly)查詢
輸出:
db.merchants.find({st:{"$regex" : "cr", "$options": "i"}}, {n:1, _id:1})
{ "n" : "Crab shack", "_id" : ObjectId("51c908cc1925f3ca51000001") }
{ "n" : "Tacos R Us", "_id" : ObjectId("51c16f201925f3df4300001b") }
db.merchants.find({st:{"$regex" : "cr", "$options": "i"}}, {n:1, _id:1}).explain()
{
"cursor" : "BtreeCursor st_1_n_1__id_1 multi",
"isMultiKey" : false,
"n" : 2,
"nscannedObjects" : 2,
"nscanned" : 2,
"nscannedObjectsAllPlans" : 2,
"nscannedAllPlans" : 2,
"scanAndOrder" : false,
"indexOnly" : true,
"nYields" : 0,
"nChunkSkips" : 0,
"millis" : 0,
"indexBounds" : {
"st" : [
[
"",
{
}
],
[
/cr/i,
/cr/i
]
],
"n" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"_id" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
]
},
"server" : "MacBook-Pro.local:27017"
}
但是從使用mongoid軌道控制檯運行的同一查詢給我:
Merchant.where({:st => { '$regex'=> "cr", '$options' => 'i' } }).only(:_id, :n).explain
=> {
"cursor"=>"BtreeCursor st_1_n_1__id_1 multi",
"isMultiKey"=>false,
"n"=>2,
"nscannedObjects"=>2,
"nscanned"=>2,
"nscannedObjectsAllPlans"=>2,
"nscannedAllPlans"=>2,
"scanAndOrder"=>false,
"indexOnly"=>false,
"nYields"=>0,
"nChunkSkips"=>0,
"millis"=>0,
"indexBounds"=>{
"st"=>[["", {}], [/cr/i, /cr/i]],
"n"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]], "_id"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]]
},
"allPlans"=>[{"cursor"=>"BtreeCursor st_1_n_1__id_1 multi", "n"=>2, "nscannedObjects"=>2, "nscanned"=>2, "index
Bounds"=>{"st"=>[["", {}], [/cr/i, /cr/i]], "n"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]], "_id"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]]}}], "oldPlan"=>{"cursor"=>"Btr
eeCursor st_1_n_1__id_1 multi", "indexBounds"=>{"st"=>[["", {}], [/cr/i, /cr/i]], "n"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]], "_id"=>[[{"$minElement"=>1}, {"$maxElement
"=>1}]]}}, "server"=>"Arvinds-MacBook-Pro.local:27017"}
我懷疑這是因爲只有()改性劑。或者這是一個錯誤?
編輯: 我使用Mongoid v3.1.4和mongod的V2.2
這裏是mongod的查詢從mongoid看到: 週一7月15日10時47分26秒[conn14] runQuery稱爲spl_development .merchants {$ query:{st:{$ regex:「cr」,$ options:「i」}},$ explain:true} Mon Jul 15 10:47:26 [conn14] query spl_development.merchants query:{ $ query:{st:{$ regex:「cr」,$ options:「i」}},$ explain:true} ntoreturn:0 keyUpdates:0 locks(micros)r:212 nreturned:1 reslen:393 0ms
所以投影沒有被髮送到mongod層,只在應用程序中處理它層。不理想!
您是否嘗試啓用mongod日誌並查看mongoid發送給服務器的查詢? –
你使用的是什麼版本的mongod?看起來像你得到不正確的nscannedObjects,這表明比當前版本更舊。 –