[TINKERPOP-1629] Allow reducing barriers in repeat()

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.3.0
• Component/s: process
• Assignee: Unassigned
• Reporter: Daniel Kuppitz
• Created: 10/Feb/17 22:16
• Updated: 28/Apr/21 19:08

Description

The following query transforms the modern graph into layers:

gremlin> g.V(1).aggregate("a").fold().store("x").unfold().both().where(without("a")).dedup().
......1>        aggregate("a").fold().store("x").unfold().both().where(without("a")).dedup().
......2>        aggregate("a").fold().store("x").unfold().both().where(without("a")).dedup().
......3>        cap("x").next()
==>[v[1]]
==>[v[3],v[2],v[4]]
==>[v[6],v[5]]

The index of each list represents the minimum distance of the vertices it contains from v[1].

There's obviously a lot of code duplication, but even worse: the max. depth has to be known upfront. repeat() could solve that, but currently fails if it contains a reducing barrier step (in OLTP and OLAP).

gremlin> g.V(1).repeat(aggregate("a").fold().store("x").unfold().both().where(without("a")).dedup()).cap("x").next()
The parent of a reducing barrier can not be repeat()-step: FoldStep