Traverse strategy breadth_first won't work with LIMIT keyword

[giacomoParigi]

I already posted a question in the issue tracker here : #5314 , but I realized that the question is too wide and decided to try and break it into smaller issues.

The first issue is a bug on the parsing of the Traverse operator. If the keyword <limit> is added, both with -1 or with an actual positive limit, the statement <strategy breadh_first> is ignored in turn, as shown by the results of these two simple queries on the GratefulDeadConcerts default database (start node is chosen randomly):

First query (without <limit>):

  select $current.traversedVertex(-1), $path from
  (
  traverse * from #9:24
    while $depth < 4

    strategy breadth_first
  ) 

Results (only first 20):

$current	$path
#9:24	(#9:24)
#9:15	(#9:24).in_followed_by0
#9:15	(#9:24).in_followed_by1
#9:15	(#9:24).in_followed_by2
#9:15	(#9:24).in_followed_by3
#9:15	(#9:24).in_followed_by4
#9:15	(#9:24).out_followed_by0
#9:15	(#9:24).out_followed_by1
#9:15	(#9:24).out_followed_by2
#9:15	(#9:24).out_followed_by3
#9:15	(#9:24).out_followed_by4
#9:15	(#9:24).out_followed_by5
#9:15	(#9:24).out_followed_by6
#9:15	(#9:24).out_followed_by7
#9:15	(#9:24).out_followed_by8
#9:15	(#9:24).out_followed_by9
#9:15	(#9:24).out_followed_by10
#9:15	(#9:24).out_followed_by11
#9:15	(#9:24).out_followed_by12
#9:15	(#9:24).out_followed_by13

Second query (with <limit>):

  select $current.traversedVertex(-1), $path from
  (
  traverse * from #9:24
    while $depth < 4
    limit -1
    strategy breadth_first
  ) 

Results (only first 20):

$current	$path
#9:24	(#9:24)
#9:15	(#9:24).in_followed_by0
#9:15	(#9:24).in_followed_by0.out(#9:15)
#9:3	(#9:24).in_followed_by0.out(#9:15).in_followed_by0
#9:4	(#9:24).in_followed_by0.out(#9:15).in_followed_by1
#9:5	(#9:24).in_followed_by0.out(#9:15).in_followed_by2
#9:11	(#9:24).in_followed_by0.out(#9:15).in_followed_by3
#9:12	(#9:24).in_followed_by0.out(#9:15).in_followed_by4
#9:14	(#9:24).in_followed_by0.out(#9:15).in_followed_by5
#9:17	(#9:24).in_followed_by0.out(#9:15).in_followed_by6
#9:16	(#9:24).in_followed_by0.out(#9:15).in_followed_by7
#9:92	(#9:24).in_followed_by0.out(#9:15).in_followed_by8
#9:109	(#9:24).in_followed_by0.out(#9:15).in_followed_by9
#9:54	(#9:24).in_followed_by0.out(#9:15).in_followed_by10
#9:83	(#9:24).in_followed_by0.out(#9:15).in_followed_by11
#9:48	(#9:24).in_followed_by0.out(#9:15).in_followed_by12
#9:53	(#9:24).in_followed_by0.out(#9:15).in_followed_by13
#9:41	(#9:24).in_followed_by0.out(#9:15).in_followed_by14
#9:160	(#9:24).in_followed_by0.out(#9:15).in_followed_by15
#9:146	(#9:24).in_followed_by0.out(#9:15).in_followed_by16

[luigidellaquila]

Hi @giacomoParigi

you should apply the LIMIT clause to the outer query, otherwise Studio will apply a 20 by default,
eg.

  select $current.traversedVertex(-1), $path from
  (
  traverse * from #9:24
    while $depth < 4
    strategy breadth_first
  ) 
  limit -1

[luigidellaquila]

I'm closing this, please reopen in case I missed something

Thanks

Luigi

[giacomoParigi]

The problem is not on the number of results (in that case you would be right pointing at the position of the LIMIT clause), but on their order. When the LIMIT clause is applied to the inner query - i.e. the TRAVERSE - the strategy falls back to the default depth_first, ignoring the following strategy statement.

[giacomoParigi]

To replicate it should be enough to copy and paste the queries - the results are from the public GratefulDeadConcerts database - but if it is useful I can add a scripted toy example.

[luigidellaquila]

ouch... ok, reopening

[luigidellaquila]

Ciao @giacomoParigi

I just pushed a fix on 2.1.x branch, it was a trivial parsing problem.
Now I'm porting the fix to develop branch

Thanks

Luigi

[luigidellaquila]

Ok, it's also fixed in develop branch.
I'm closing this, please reopen in case something is missing

Thanks

Luigi