Hash-map based GROUP BY can now process lazy inputs

[joka921]

Since #1229, QLever supports a hash-map based GROUP BY, which can be activated via the runtime parameter group-by-hash-map-enabled (which is false by default). So far, this required a fully materialized input. With this change, the input can be processed lazily. The output is still fully materialized and never lazy (because, when the input is not sorted, we cannot output any group until we have seen the last input row).

[codecov]

Codecov Report

Attention: Patch coverage is 92.75362% with 5 lines in your changes missing coverage. Please review.

Project coverage is 89.86%. Comparing base (97c195a) to head (bbed6e7).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/engine/GroupBy.cpp	92.75%	0 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1651      +/-   ##
==========================================
+ Coverage   89.84%   89.86%   +0.02%     
==========================================
  Files         389      389              
  Lines       37268    37287      +19     
  Branches     4202     4204       +2     
==========================================
+ Hits        33482    33508      +26     
+ Misses       2485     2480       -5     
+ Partials     1301     1299       -2     

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[hannahbast]

Looks good and works fine in some test queries we tried. Minor change left.

[hannahbast]

Thanks!

As a follow-up, we should find a way to enable this automatically, in particular, for queries like SELECT ?g (COUNT(?g) AS ?count) WHERE { GRAPH ?g { ?s ?p ?o } } GROUP BY ?g

[sparql-conformance]

Conformance check passed ✅

No test result changes.

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=bbed6e7afdb4aec75bd384a4b873bc6f5b9ef1e3&prev=97c195aaf9e249f43a6417f99ea93f7e94831f39

[sonarqubecloud]

Quality Gate passed

Issues
2 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