MongoDB. How to set up indexes? - mongodb

Question

Please help me with indexes in mongoDB.
There is a collection in which 800,000 documents.
There is a request that is very long runs. About 5 seconds!
{
"$or":[
{
"performer":"534ba408f9cd0ecb51711673",
"$or":[
{
"performersRole":"534ba30bf9cd0ec151a69522"
},
{
"performersRole":{
"$exists":false
}
}
]
},
{
"performersRole":"534ba30bf9cd0ec151a69522",
"notShowInToDo":{
"$ne":true
}
}
],
"taskTime":{
"$gte":1409774400,
"$lt":1409860799
},
"$and":[
{
"$or":[
{
"department":{
"$in":[
"5356134ef9cd0e4805672a15",
"53561368f9cd0e4b05645f3f",
"53a0357ff9cd0e670537c4b7",
"53a03594f9cd0e6705389449"
]
}
},
{
"department":{
"$exists":false
}
}
]
},
{
"$or":[
{
"salon":"534f7b3bf9cd0e311e77896f"
},
{
"salon":{
"$exists":false
}
}
]
}
],
"isDone":{
"$ne":true
}
}
Which indexes to add to optimize? Thanks for any advice!
Almost all documents about this format:
{
"_id": "541da66cf535a4a8569dd0ed",
"title": "test task",
"taskTime": NumberLong(1411229292),
"client": "53f876b2f535a4187f9e1264",
"salon": "534f7c3cf9cd0e91206dd948",
"track": "541da66cf535a4a8569dd0ec",
"department": "53a0357ff9cd0e670537c4b7",
"type": "invitePBP",
"performersRole": [
"534ba30bf9cd0ec151a69522"
],
"notShowInToDo": true,
"#createTime": NumberLong(1411229292),
"#updateTime": NumberLong(1411229292)
}

Answer 1

Before the creation of index, consider following points:
1. Cut down the number of query hierarchy as possible as you can;
2. Avoid to use $add and $or if possible;
3. Avoid to use $exists if possible as it will access the collection even though having index on the field;
4. Design the index according to the sequence executed as you want to.
Suppose I have understood your requirements correctly, then I reconstruct the query as below:
var query = {
"taskTime" : {
"$gte" : 1409774400,
"$lt" : 1409860799
},
"isDone" : {
"$ne" : true
},
"$and" : [
{
"salon" : {
"$in" : [ null, "534f7b3bf9cd0e311e77896f" ]
}
}, {
"department" : {
"$in" : [ null,
"5356134ef9cd0e4805672a15",
"53561368f9cd0e4b05645f3f",
"53a0357ff9cd0e670537c4b7",
"53a03594f9cd0e6705389449" ]
}
}],
"$or" : [ {
"performer" : "534ba408f9cd0ecb51711673",
"performersRole" : {
"$in" : [ null, "534ba30bf9cd0ec151a69522" ]
}
}, {
"performersRole" : "534ba30bf9cd0ec151a69522",
"notShowInToDo" : {
"$ne" : true
}
} ]
};
Be careful of null:
Be attentioned that {"salon" : {"$in" : [ null, "534f7b3bf9cd0e311e77896f" ]} can work completely on index {salon:1} in v2.4 but will still access the collection in v2.6, I don't know the exact reason but just guess that it's possible to the definition of null has been changed (include undefined type).
To avoid this issue in v2.6, an alternative is to initialize a real value to field salon instead of doing nothing.
You can try this way to create index and your feedback is appriciated since I haven't the real data to make a test.
db.c.ensureIndex({taskTime:1, isDone:1, salon:1, department:1}, {name:"bigIndex"});
Add my test result - 1010,000 documents
var a = {
"taskTime" : {
"$gte" : 1410443932781,
"$lt" : 1412443932781
},
"isDone" : {
"$ne" : true
},
"$and" : [
{
"salon" : {
"$in" : [ null, "534f7b3bf9cd0e311e77896f", "5420ecdc218ba2fb5353ad5b" ]
}
}, {
"department" : {
"$in" : [ null,
"5356134ef9cd0e4805672a15",
"53561368f9cd0e4b05645f3f",
"53a0357ff9cd0e670537c4b7", "5420ecdc218ba2fb5353ad5d",
"53a03594f9cd0e6705389449" ]
}
}],
"$or" : [ {
"performer" : "534ba408f9cd0ecb51711673",
"performersRole" : {
"$in" : [ null, "5420ecdc218ba2fb5353ad5e" ]
}
}, {
"performersRole" : "5420ecdc218ba2fb5353ad5e",
"notShowInToDo" : {
"$ne" : true
}
} ]
};
db.c.find(a).explain();
{
"cursor" : "BtreeCursor bigIndex",
"isMultiKey" : false,
"n" : 1,
"nscannedObjects" : 1,
"nscanned" : 54290,
"nscannedObjectsAllPlans" : 1,
"nscannedAllPlans" : 54290,
"scanAndOrder" : false,
"indexOnly" : false,
"nYields" : 425,
"nChunkSkips" : 0,
"millis" : 261,
"indexBounds" : {
"taskTime" : [
[
1410443932781,
1412443932781
]
],
"isDone" : [
[
{
"$minElement" : 1
},
true
],
[
true,
{
"$maxElement" : 1
}
]
],
"salon" : [
[
null,
null
],
[
"534f7b3bf9cd0e311e77896f",
"534f7b3bf9cd0e311e77896f"
],
[
"5420ecdc218ba2fb5353ad5b",
"5420ecdc218ba2fb5353ad5b"
]
],
"department" : [
[
null,
null
],
[
"5356134ef9cd0e4805672a15",
"5356134ef9cd0e4805672a15"
],
[
"53561368f9cd0e4b05645f3f",
"53561368f9cd0e4b05645f3f"
],
[
"53a0357ff9cd0e670537c4b7",
"53a0357ff9cd0e670537c4b7"
],
[
"53a03594f9cd0e6705389449",
"53a03594f9cd0e6705389449"
],
[
"5420ecdc218ba2fb5353ad5d",
"5420ecdc218ba2fb5353ad5d"
]
]
},
"server" : "Mars-PC:27017",
"filterSet" : false
}