【发布时间】：2020-10-01 16:06:09
【问题描述】：
我遇到了一种特殊情况，其中一个查询似乎是在进行内存排序。查询 1 是执行内存排序的查询，而查询 2 正确执行合并排序。
查询有几个部分，所以我想知道哪个部分导致查询排序在内存中完成？
我确实有一个解决方法，但我想知道这背后的原因。它们都有 2 个输入级，所以我不确定是什么原因。
架构：
schema = {
date: Date, // date that can change
createTime: Date, // create time of document
value: Number
}
索引：
schema.index({value: 1, createTime: -1, date: 1});
查询 1：我在顶层有 $or 以避免使用不正确的索引：MongoDB query to slow when using $or operator
db.getCollection('dates').find({
$or: [
{value: {$in: [1, 2]}, date: null},
{value: {$in: [1, 2]}, date: {$gt: ISODate("2020-06-16T23:59:59.999Z")}}
]
}).sort({createTime:-1}).explain()
查询 1 计划：如您所见，它在内存中进行排序。我不确定发生这种情况的确切原因。
{
"stage" : "SUBPLAN",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "SORT",
"sortPattern" : {
"createTime" : -1.0
},
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "OR",
"inputStages" : [
{
"stage" : "FETCH",
"filter" : {
"date" : {
"$eq" : null
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"value" : 1,
"createTime" : -1,
"date" : 1
},
"indexName" : "value_1_createTime_-1_date_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"value" : [],
"createTime" : [],
"date" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"value" : [
"[1.0, 1.0]",
"[2.0, 2.0]"
],
"createTime" : [
"[MaxKey, MinKey]"
],
"date" : [
"[undefined, undefined]",
"[null, null]"
]
}
}
},
{
"stage" : "IXSCAN",
"keyPattern" : {
"value" : 1,
"createTime" : -1,
"date" : 1
},
"indexName" : "value_1_createTime_-1_date_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"value" : [],
"createTime" : [],
"date" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"value" : [
"[1.0, 1.0]",
"[2.0, 2.0]"
],
"createTime" : [
"[MaxKey, MinKey]"
],
"date" : [
"(new Date(1592351999999), new Date(9223372036854775807)]"
]
}
}
]
}
}
}
}
}
查询 2：
db.getCollection('dates').find({
value: {$in: [1, 2]},
date: {$not: {$lte: ISODate("2020-06-16T23:59:59.999Z")}}
}).sort({createTime:-1}).explain()
查询 2 计划：我使用的解决方法查询，它成功进行了合并排序。
{
"stage" : "FETCH",
"inputStage" : {
"stage" : "SORT_MERGE",
"sortPattern" : {
"createTime" : -1.0
},
"inputStages" : [
{
"stage" : "IXSCAN",
"keyPattern" : {
"value" : 1,
"createTime" : -1,
"date" : 1
},
"indexName" : "value_1_createTime_-1_date_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"value" : [],
"createTime" : [],
"date" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"value" : [
"[1.0, 1.0]"
],
"createTime" : [
"[MaxKey, MinKey]"
],
"date" : [
"[MinKey, true]",
"(new Date(1592351999999), MaxKey]"
]
}
},
{
"stage" : "IXSCAN",
"keyPattern" : {
"value" : 1,
"createTime" : -1,
"date" : 1
},
"indexName" : "value_1_createTime_-1_date_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"value" : [],
"createTime" : [],
"date" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"value" : [
"[2.0, 2.0]"
],
"createTime" : [
"[MaxKey, MinKey]"
],
"date" : [
"[MinKey, true]",
"(new Date(1592351999999), MaxKey]"
]
}
}
]
}
}
【问题讨论】：
标签： mongodb sorting mongoose indexing mongodb-query