我有一个包含地理JSON点坐标数据的集合,需要查询在某个区域内最新的10个条目。现在有100万条目,但将来会增加到约10倍。
当所需区域内有大量条目时,我的查询性能会急剧下降(情况3)。我目前使用的测试数据是随机的,但真实数据不会这样,因此不能仅基于区域维度选择另一个索引(如情况4)。
为了使其无论区域如何都能表现出可预测的性能,我该怎么做?
1.集合统计信息:
当所需区域内有大量条目时,我的查询性能会急剧下降(情况3)。我目前使用的测试数据是随机的,但真实数据不会这样,因此不能仅基于区域维度选择另一个索引(如情况4)。
为了使其无论区域如何都能表现出可预测的性能,我该怎么做?
1.集合统计信息:
> db.randomcoordinates.stats()
{
"ns" : "test.randomcoordinates",
"count" : 1000000,
"size" : 224000000,
"avgObjSize" : 224,
"storageSize" : 315006976,
"numExtents" : 15,
"nindexes" : 3,
"lastExtentSize" : 84426752,
"paddingFactor" : 1,
"systemFlags" : 0,
"userFlags" : 0,
"totalIndexSize" : 120416128,
"indexSizes" : {
"_id_" : 32458720,
"position_2dsphere_timestamp_-1" : 55629504,
"timestamp_-1" : 32327904
},
"ok" : 1
}
2. 索引:
> db.randomcoordinates.getIndexes()
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"ns" : "test.randomcoordinates",
"name" : "_id_"
},
{
"v" : 1,
"key" : {
"position" : "2dsphere",
"timestamp" : -1
},
"ns" : "test.randomcoordinates",
"name" : "position_2dsphere_timestamp_-1"
},
{
"v" : 1,
"key" : {
"timestamp" : -1
},
"ns" : "test.randomcoordinates",
"name" : "timestamp_-1"
}
]
3. 使用2dsphere复合索引查找:
> db.randomcoordinates.find({position: {$geoWithin: {$geometry: {type: "Polygon", coordinates: [[[1, 1], [1, 90], [180, 90], [180, 1], [1, 1]]]}}}}).sort({timestamp: -1}).limit(10).hint("position_2dsphere_timestamp_-1").explain()
{
"cursor" : "S2Cursor",
"isMultiKey" : true,
"n" : 10,
"nscannedObjects" : 116775,
"nscanned" : 283424,
"nscannedObjectsAllPlans" : 116775,
"nscannedAllPlans" : 283424,
"scanAndOrder" : true,
"indexOnly" : false,
"nYields" : 4,
"nChunkSkips" : 0,
"millis" : 3876,
"indexBounds" : {
},
"nscanned" : 283424,
"matchTested" : NumberLong(166649),
"geoTested" : NumberLong(166649),
"cellsInCover" : NumberLong(14),
"server" : "chan:27017"
}
4. 通过时间戳索引查找:
> db.randomcoordinates.find({position: {$geoWithin: {$geometry: {type: "Polygon", coordinates: [[[1, 1], [1, 90], [180, 90], [180, 1], [1, 1]]]}}}}).sort({timestamp: -1}).limit(10).hint("timestamp_-1").explain()
{
"cursor" : "BtreeCursor timestamp_-1",
"isMultiKey" : false,
"n" : 10,
"nscannedObjects" : 63,
"nscanned" : 63,
"nscannedObjectsAllPlans" : 63,
"nscannedAllPlans" : 63,
"scanAndOrder" : false,
"indexOnly" : false,
"nYields" : 0,
"nChunkSkips" : 0,
"millis" : 0,
"indexBounds" : {
"timestamp" : [
[
{
"$maxElement" : 1
},
{
"$minElement" : 1
}
]
]
},
"server" : "chan:27017"
}
有人建议使用{timestamp: -1, position: "2dsphere"}
索引,所以我也尝试了一下,但似乎表现还不够好。
5. 使用时间戳和2dsphere复合索引进行查找
> db.randomcoordinates.find({position: {$geoWithin: {$geometry: {type: "Polygon", coordinates: [[[1, 1], [1, 90], [180, 90], [180, 1], [1, 1]]]}}}}).sort({timestamp: -1}).limit(10).hint("timestamp_-1_position_2dsphere").explain()
{
"cursor" : "S2Cursor",
"isMultiKey" : true,
"n" : 10,
"nscannedObjects" : 116953,
"nscanned" : 286513,
"nscannedObjectsAllPlans" : 116953,
"nscannedAllPlans" : 286513,
"scanAndOrder" : true,
"indexOnly" : false,
"nYields" : 4,
"nChunkSkips" : 0,
"millis" : 4597,
"indexBounds" : {
},
"nscanned" : 286513,
"matchTested" : NumberLong(169560),
"geoTested" : NumberLong(169560),
"cellsInCover" : NumberLong(14),
"server" : "chan:27017"
}