Optimize binding of multiple columns in transitive paths

[schaetzr]

This PR aims to improve query planning for special queries where both sides of a triple are already bound (= are variables that have values already assigned to them). Currently, this would invoke a scan over the whole dataset and then execute a multi-column join instead of picking one column as start node and thereby vastly improving query runtime.

Example:

PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>
SELECT * WHERE {
  VALUES (?s ?o) {(wd:Q2 wd:Q1)} .
  ?s wdt:P361* ?o
}

... creates a multicolumn join, but it'd be better if it ran like:

PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>
SELECT * WHERE {
  VALUES (?s) {(wd:Q2)} .
  ?s wdt:P361* wd:Q1
}

which instead calls a transitive path operation in the query planer.

This PR is WIP and currently, nothing regarding this optimization is working as expected. Tests should also fail.

[schaetzr]

In the first attempt, I tried to make the bindLeftOrRightSide function inside the TransitivePathBase accept a second column, however, I am currently running into the following error:

Assertion `!plan->variableColumns_.contains(variable)` failed. Please report this to the developers. In file "/bproj/qlever/src/engine/TransitivePathBase.cpp " at line 640

This happens on my toy example dataset:

<Q1> <P1> <Q2> .
<Q2> <P1> <Q3> .
<Q1> <P1> <Q1> .

with the query

SELECT * WHERE {
  VALUES (?s ?o) {(<Q1> <Q2>)} .
  ?s <P1>* ?o 
}

i am working on finding out what mistake I made and how to fix the error

[sparql-conformance]

Overview

Number of Tests	Passed ✅	Intended ✅	Failed ❌	Not tested
548	445	73	30	0

Conformance check failed ❌

Test Status Changes 📊

Number of Tests	Previous Status	Current Status
2	Passed	Failed

Details: https://qlever.dev/sparql-conformance-ui?cur=9f8f19f123717da6e7f5cc6e03a29a017318235d&prev=b2f2e101de954c81794a5c4167f9f404da689ff0

[sonarqubecloud]

Quality Gate passed

Issues
5 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud