我有一个类似下面的查询。显然，更好的索引是“platform_1_keyuserAccountID_1_weiboAccountID_1_postTime_1”，但是mongodb选择“weiboAccountID_1”，我做错了什么？
db.inbox_weibo.find({platform: "sina", keyuserAccountID:"1665337047", weiboAccountID: "2271338624"}).explain(true);
{
"cursor" : "BtreeCursor weiboAccountID_1",
"isMultiKey" : false,
"n" : 1,
"nscannedObjects" : 1,
"nscanned" : 1,
"nscannedObjectsAllPlans" : 24,
"nscannedAllPlans" : 634425,
"scanAndOrder" : false,
"indexOnly" : false,
"nYields" : 1,
"nChunkSkips" : 0,
"millis" : 2912,
"indexBounds" : {
"weiboAccountID" : [
[
"2271338624",
"2271338624"
]
]
},
"allPlans" : [
{
"cursor" : "BtreeCursor weiboAccountID_1",
"isMultiKey" : false,
"n" : 1,
"nscannedObjects" : 1,
"nscanned" : 1,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"weiboAccountID" : [
[
"2271338624",
"2271338624"
]
]
}
},
{
"cursor" : "BtreeCursor platform_1_keyuserAccountID_1_dealed_1_operatorID_1_weiboAccountID_1_postTIme_-1",
"isMultiKey" : false,
"n" : 1,
"nscannedObjects" : 1,
"nscanned" : 62,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealed" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"operatorID" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"weiboAccountID" : [
[
"2271338624",
"2271338624"
]
],
"postTIme" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor platform_1_keyuserAccountID_1_weiboAccountID_1_postTime_-1",
"isMultiKey" : false,
"n" : 1,
"nscannedObjects" : 1,
"nscanned" : 1,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"weiboAccountID" : [
[
"2271338624",
"2271338624"
]
],
"postTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor platform_keyuserAccountID_dealed_postTime_weiboAccountID",
"isMultiKey" : false,
"n" : 1,
"nscannedObjects" : 1,
"nscanned" : 634331,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealed" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"postTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
],
"weiboAccountID" : [
[
"2271338624",
"2271338624"
]
]
}
},
{
"cursor" : "BtreeCursor platform_1_keyuserAccountID_1_mid_1",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"mid" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor platform_1_keyuserAccountID_1_dealerID_1",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealerID" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor distinctAccountAgg",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealed" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"operatorID" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"postTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor fansCountUndealed",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealed" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"fromType" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"fansCount" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
],
"postTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
],
"usePicture" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor retweetCountUndealed",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealed" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"fromType" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"sourceRetweetCount" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
],
"postTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
],
"usePicture" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor interactUndealed",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealed" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"fromType" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"userInteractionCount" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
],
"postTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
],
"usePicture" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor platform_1_keyuserAccountID_1_dealed_1_dealTime_-1",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealed" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"dealTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor platform_1_keyuserAccountID_1_dealerID_1_postTime_-1",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealerID" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"postTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor platform_1_keyuserAccountID_1_postTime_-1",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"platform" : [
[
"sina",
"sina"
]
],
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"postTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
]
}
},
{
"cursor" : "BtreeCursor keyuserAccountID_dealed_createTime_-1",
"isMultiKey" : false,
"n" : 0,
"nscannedObjects" : 2,
"nscanned" : 3,
"scanAndOrder" : false,
"indexOnly" : false,
"nChunkSkips" : 0,
"indexBounds" : {
"keyuserAccountID" : [
[
"1665337047",
"1665337047"
]
],
"dealed" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"createTime" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
]
}
}
答案 0 :(得分：1)
我不认为其他指数“更好”。似乎两个索引（你建议使用的那个和mongodb使用的索引）都会使用“nscanned：1”返回查询的对象，因此它们对于此查询同样完美。我说因为你的测试数据集中的“weiboAccountID”确切地定义了你正在寻找的那条记录，所以在这种情况下不需要其他索引 - mongodb会选择第一个合适的。尝试使用相同的weiboAccountID添加更多记录（如果重复的ID在您的数据集中完全有效）并重新运行查询，请查看它如何更改执行。