Rid Bag threshold and strategy for fetching and assembling data

[Davide Neri]

Hi,

I am developing a web app on node.js and using OrientDB.

For some functionalities I need to make queries on a structure like this:

User (V)

Post (V)

author (E)

User -- author --› Post

And queries should retrieve the User(s) element(s) and the posts he is author of...all in the same structure:

[ {

    @rid: #9:1,

    @class: User,

    name: user1,

    posts: [ {

                   @rid: #10:1,

                   @class: Post,

                   name: post1

                 }, {

                   @rid: #10:2,

                   @class: Post,

                   name: post2

                 } ]

  }, {

    @rid: #9:2,

    @class: User,

    name: user2,

    posts: [ ... ]

  } ]

Basically, I'm currently doing this in 2 steps:

select * from User where ...

where I get something like:

[ {

    @rid: #9:1,

    @class: User,

    name: user1,

    out_author: [#10:1, #10:2]

  }, {

    @rid: #9:2,

    @class: User,

    name: user2,

    out_author: [#10:3, #10:3]

  } ]

From this result I collect all the rids of the first query and make a second query:

select expand(out('author')) from Post where @rid in [USERS_RIDS]

where I get something like:

[ {

    @rid: #10:1,

    @class: Post,

    name: post1

  }, {

    @rid: #10:2,

    @class: Post,

    name: post2

  } ]

And in the end I merge the results of the two queries by matching the @rids in out_author of the first results and @rids of the Posts in the second results.

This all works well, until I have just a few edges.. but when edges start to become more than 40 the out_author becomes blank...and my whole algorithm breaks. So here are my two questions:

- I was reading that to have more rids returned I need to change the RID_BAG_EMBEDDED_TO_SBTREEBONSAI_THRESHOLD to a bigger number... I tried to change the orientdb-server-config.xml adding an entry in properties....but I can't see any results. I'm pretty sure I'm adding a wrong entry, but I can't understand any clear explanation of what I should do. Do you know what exactly should I do to change this value?

- Also... is there another better way to achieve the same result I need to have with my algorithm? Is it possible to be achieved with a single query or in some way that doesn't rely on matching rids?

Thank you very much for your help!

[Johan Sjöberg]

A better way could be:

select *, $posts 

from User 

let $posts = (select expand(in('author')) from $parent.$current)

where username = ..

The $parent.$current would be a specific user, you then expand the edge to the posts. Which you then return as $posts

Not entirely sure of the direction of you edge but I'm sure you figure it out!

I know nothing about RID_BAG_EMBEDDED_TO_SBTREEBONSAI_THRESHOLD  thou.

/ Johan

[Davide Neri]

Wow, thank you,

I just tried it and this goes around the limit problem, so it is definitely a possible solution!

If anybody knows how to set the Rid Bag threshold higher, would be probably faster and lighter on the server as it would use only a simple query.

Otherwise at least for now I might implement this solution. Thanks again

[d]

[Davide Neri]

Heyhey,

With this query I'm able to get only the RIDs of the linked vertices going around the RID Bag limits, but I still need to fetch linked vertex with another query later.

I would have thought that, since there is an expand(in(...)) it would have returned the vertices and not their RIDs only, but I must be wrong : D

Do you know a way to have the result all in once, avoiding the use of a second query and nested loops?

Aaaand... otherwise, does anybody know how to change RID_BAG_EMBEDDED_TO_SBTREEBONSAI_THRESHOLD value?

[user.w...@gmail.com]

Hi Davide,

Try this:

select *, @this.toJSON('rid,version,fetchPlan:[*]out_author:-1 [*]in_author*:-2') from User where name = "user1"

Regards,

Michela