Query response time very high

fasal · October 26, 2019, 7:28am

Hi I'm running following query on dataset of count 44,000 (mongodb)

SELECT ?seqId {
GRAPH virtual://aus {
?images :existence "0707" ;
:seqId ?seqId .
}
}
LIMIT 50

Its taking almost 2 minutes to get the response. Is this the usual behavior or is there something i have to do to make it run faster...?

zachary.whitley · October 26, 2019, 1:13pm

What version of stardog are you running and can share the query plan?

Stardog query explain

fasal · October 26, 2019, 6:22pm

I'm using 7.0.1 @zachary.whitley

Plan is
Slice(offset=0, limit=50) [#50]
`─ Projection(?seqId) [#18K]
   `─ Projection(?images, ?seqId) [#18K]
      `─ ServiceJoin [#18K]
         +─ VirtualGraphMongoDB<virtual://austria> [#36212] {
         │  +─ Query=
         │  +─    { $match : {$and : [ {"frameId" : {$exists : true, $ne : null}}, {"seqId" : {$exists : true, $ne : null}} ]} },
         │  +─    {$project: {frameId: '$frameId', seqId: '$seqId'} }
         │  +─ Vars=
         │  +─    ?seqId <- COLUMN($1)^^xsd:string
         │  +─    ?var100 <- COLUMN($0)^^xsd:string
         │  }
         `─ VirtualGraphMongoDB<virtual://austria> [#9053] {
            +─ Query=
            +─    {$unwind: "$existence"},
            +─    { $match : {$and : [ {"existence" : {$eq : "0707"}}, {"frameId" : {$exists : true, $ne : null}} ]} },
            +─    {$project: {frameId: '$frameId'} }
            +─ Vars=
            +─    ?images <- TEMPLATE(http://austria.com/images/{frameId/0})
            +─    ?var100 <- COLUMN($0)^^xsd:string
            }

zachary.whitley · October 26, 2019, 6:35pm

It looks like it's breaking it into two separate queries and doing a ServiceJoin which probably isn't very performant. I'm not sure why. You might want to include you mapping if you can so you can avoid a round trip when someone more knowledgable about this takes a look at this. You might also want to add some details about your mongodb setup, schema, indexes, etc

fasal · October 26, 2019, 9:06pm

Okay.. I have shared mapping file and schema.. let me know if anything else is required

Mapping
    FROM JSON {
      "aus":{
        "_id": "?imageId",
        "frameId": "?frameId",
        "frameNo": "?frameNo",
        "seqId": "?seqId", 
        "existence": ["?existence"],
        "edge": ["?edge"],
        "population": ["?population"],
        "nearEdge": ["?nearEdge"],
        "farEdge": ["?farEdge"],
        "centerDirection": ["?centerDirection"],
        "leftDirection":["?leftDirection"],
        "rightDirection": ["?rightDirection"], 
        "dualTruncation":["?dualTruncation"],
        "leftTruncation": ["?leftTruncation"],
        "rightTruncation": ["?rightTruncation"],
        "entropy": "?entropy",
        "roadEntropy": "?roadEntropy"
      }
    }
    TO {
    ?image a :Images;
            :_id  ?imageId;
            :frameId ?frameId;
            :frameNo "?frameNo"^^xsd:integer;
            :seqId ?seqId;
            :existence ?existence;
            :edge ?edge;
            :population ?population;
            :nearEdge ?nearEdge;
            :farEdge ?farEdge;
            :centerDirection ?centerDirection;
            :leftDirection ?leftDirection;
            :rightDirection ?rightDirection;
            :dualTruncation ?dualTruncation;
            :leftTruncation ?leftTruncation;
            :rightTruncation ?rightTruncation;
            :entropy "?entropy"^^xsd:integer;
            :roadEntropy "?roadEntropy"^^xsd:integer;
        }
    WHERE {
      BIND (template("http://austria.com/images/{frameId}") AS ?image)
    }

Have attached screen shot of schema

fasal · October 28, 2019, 9:39am

Any help on this?
cc @zachary.whitley

PaulJackson · October 28, 2019, 1:19pm

Hi Fasal,

This happens because frameId is not known to be a unique field. frameId is the field that's used to create the IRI for ?image, which in turn is the variable we're joining on in the query.

If frameId is not a unique field in the aus collection, then Stardog needs this join to create the cross product of existence and seqId fields per frameId.

If this is not what's intended, you have a couple options, depending on your data, what it means, and how you wish to model it.

If the combination of the _id and frameId fields represent some concept (an image element, say) you could change your model such that each aus document represents an "ImageFrame" with an IRI who's template includes both the _id and frameId fields. See this blog post for a detailed explanation: Mapping Denormalized Data | Stardog

If there is a 1 to 1 relationship between frames and documents (between the frameId field and the _id field), then you have a couple choices.

You could use the _id field in place of the frameId field in the image template.
You could indicate to Stardog that frameId is a unique field in aus collection using the unique.key.sets virtual graph property.

In this example, the property would be set to:
unique.key.sets=(aus.[].frameId)

See Home | Stardog Documentation Latest for details.

-Paul

fasal · October 29, 2019, 3:13pm

Hi @PaulJackson,

Thanks for the response..
frameId is unique in my dataset but as you suggested I tried following things:

I did set unique.key.sets=(aus.[].frameId) in my stardog studio virtual graph configuration options under other options as property & value keys..
Output:- I couldn't find any improvement in the response time of the query.
Then i tried using _id in place of frameId field to create IRI
WHERE { BIND (template("http://austria.com/images/{_id}") AS ?image) }

In this case simple query like

SELECT * {GRAPH <virtual://austria> { ?image a :Images ; :frameId ?frameId ;}}

fetches around 44k records in just a second which is what i'm looking for.. But now when i add one more condition to this query I don't get any output.. This happens when I try to add a condition from any of the array fields (in this query existence is an array object)..

SELECT * {GRAPH <virtual://austria> {?image a :Images ; :frameId ?frameId ; :existence "0707" .}}

I just see header fields as image and frameId without any data.

Observation: In 2nd case queries are working fine if I query only on int and string fields but when I'm including array objects not able to see any result..

Other option you suggested was combination of frameId and _id for IRI, again with this change query is behaving like 2nd case..

Not sure where i'm going wrong!!!

jess · October 29, 2019, 3:16pm

Hi Fasal,

The inclusion of [] in the unique.key.sets property indicates an array.

What was the result of using _id in the subject? Can you share the query plan?

jess · October 29, 2019, 3:18pm

I was wrong about the []. Can you include the query plan for both changes you tried?

fasal · October 29, 2019, 3:36pm

I have updated my response above @jess please have a re-look

jess · October 29, 2019, 3:41pm

Hi Fasal,

It sounds like you're describing a case where you query for images where one of the values of the existence field is "0707". You used this query as an example:

SELECT * {GRAPH <virtual://austria> {
?image a :Images ; :frameId ?frameId ; :existence "0707" .}}

Can you share the query plan for this query?

What result do you get if you replace the constant value for existence with a variable, eg:

SELECT * {GRAPH <virtual://austria> {
?image a :Images ; :frameId ?frameId ; :existence ?existence .}}

What values are bound to the ?existence variable?

fasal · October 29, 2019, 3:53pm

@jess query plan

   ` Projection(?image, ?frameId) [#9.1K]
    `─ Projection(?image, ?frameId) [#9.1K]
       `─ ServiceJoin [#9.1K]
          +─ VirtualGraphMongoDB<virtual://austria> [#36212] {
          │  +─ Query=
          │  +─    { $match : {$and : [ {"_id" : {$exists : true, $ne : null}}, {"frameId" : {$exists : true, $ne : null}} ]} },
          │  +─    {$project: {_id: '$_id', frameId: '$frameId'} }
          │  +─ Vars=
          │  +─    ?image <- TEMPLATE(http://austria.com/images/{_id/0})
          │  +─    ?frameId <- COLUMN($1)^^xsd:string
          │  +─    ?var100 <- COLUMN($0)^^xsd:string
          │  }
          `─ VirtualGraphMongoDB<virtual://austria> [#9053] {
             +─ Query=
             +─    {$unwind: "$existence"},
             +─    { $match : {$and : [ {"existence" : {$eq : "0707"}}, {"_id" : {$exists : true, $ne : null}} ]} },
             +─    {$project: {_id: '$_id'} }
             +─ Vars=
             +─    ?var100 <- COLUMN($0)^^xsd:string
             } `

for this query
SELECT * {GRAPH virtual://austria {
?image a :Images ; :frameId ?frameId ; :existence ?existence .}}
Nothing gets displayed

fasal · October 29, 2019, 3:58pm

Deleted!!!!!!!!!!!!!!!!!!!!!!

jess · October 29, 2019, 4:19pm

Do you get results for this query:

?image :existence ?existence

fasal · October 29, 2019, 4:25pm

@jess No results... nothing gets displayed .

query plan follows:

Projection(?image, ?frameId, ?existence) [#72K]
─ Projection(?image, ?frameId, ?existence) [#72K] ─ ServiceJoin [#72K]
+─ VirtualGraphMongoDBvirtual://austria [#54319] {
│ +─ Query=
│ +─ {$unwind: "$existence"},
│ +─ { $match : {$and : [ {"_id" : {$exists : true, $ne : null}}, {"existence" : {$exists : true, $ne : null}} ]} }
│ +─ Vars=
│ +─ ?existence <- COLUMN($1)^^xsd:string
│ +─ ?var100 <- COLUMN($0)^^xsd:string
│ }
`─ VirtualGraphMongoDBvirtual://austria [#36212] {
+─ Query=
+─ { $match : {$and : [ {"_id" : {$exists : true, $ne : null}}, {"frameId" : {$exists : true, $ne : null}} ]} },
+─ {$project: {_id: '$_id', frameId: '$frameId'} }
+─ Vars=
+─ ?image <- TEMPLATE(http://austria.com/images/{_id/0})
+─ ?frameId <- COLUMN($1)^^xsd:string
+─ ?var100 <- COLUMN($0)^^xsd:string
}

jess · October 29, 2019, 4:27pm

SELECT * {GRAPH <virtual://austria> {
?image :existence ?existence .}}

Please use this exact query. Can you share the query plan?

fasal · October 29, 2019, 4:31pm

Oh okay!! yeah i got the results for

SELECT * {GRAPH virtual://austria {
?image :existence ?existence .}}

plan is

Projection(?image, ?existence) [#54K]
`─ VirtualGraphMongoDBvirtual://austria [#54319] {
+─ Query=
+─ {$unwind: "$existence"},
+─ { $match : {$and : [ {"_id" : {$exists : true, $ne : null}}, {"existence" : {$exists : true, $ne : null}} ]} }
+─ Vars=
+─ ?image <- TEMPLATE(http://austria.com/images/{_id/0})
+─ ?existence <- COLUMN($1)^^xsd:string
}

jess · October 29, 2019, 4:34pm

Great, and what about if you include the constant:

SELECT * {GRAPH <virtual://austria> {
?image :existence "0707" .}}

fasal · October 29, 2019, 4:36pm

Yes records are displayed following is the query plan

Projection(?image) [#9.1K]
`─ VirtualGraphMongoDBvirtual://austria [#9053] {
+─ Query=
+─ {$unwind: "$existence"},
+─ { $match : {$and : [ {"existence" : {$eq : "0707"}}, {"_id" : {$exists : true, $ne : null}} ]} },
+─ {$project: {_id: '$_id'} }
+─ Vars=
+─ ?image <- TEMPLATE(http://austria.com/images/{_id/0})
}

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