fix: optimize queries with leading unbounded expansion BED-8779

[urangel]

Description

This changeset implements an optimization strategy for multistep traversals which begin with an unbounded expansion such that the query is first flipped in direction before translating into pg sql.

The idea is that a more tightly defined end is better for selectivity since this circumvents first continuing down an indefinite expansion which may or may not satisfy later evaluated constraints.

We already do some traversal direction reversing within a traversal step itself so this a similar approach but affecting the entire traversal rather than only step by step.

Resolves: BED-8779

Type of Change

• Chore (a change that does not modify the application functionality)
• Bug fix (a change that fixes an issue)
• New feature / enhancement (a change that adds new functionality)
• Refactor (no behaviour change)
• Test coverage
• Build / CI / tooling
• Documentation

Testing

• Unit tests added / updated
• Integration tests added / updated
• Full test suite run (make test_all with CONNECTION_STRING set)

Screenshots (if appropriate):

Driver Impact

• PostgreSQL driver (drivers/pg)
• Neo4j driver (drivers/neo4j)

Checklist

• Code is formatted
• All existing tests pass
• go.mod / go.sum are up to date if dependencies changed

Summary by CodeRabbit

• New Features

  • Improved traversal planning by starting eligible variable-length searches from more selective endpoints.
  • Preserved the original logical path order when traversals are optimized in reverse.
  • Added relationship uniqueness handling to prevent reused edges during path expansion.

• Bug Fixes

  • Prevented recursive path segments from reusing previously matched relationships.
  • Improved path reconstruction and filtering for multipart and repeated patterns.

• Tests

  • Added coverage for traversal reversal, path reuse prevention, endpoint constraints, and unsupported reversal scenarios.

[coderabbitai]

Note

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⚙️ Run configuration

Configuration used: Organization UI

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Run ID: 627084fc-203a-4852-a7f8-ff5d06f86b84

📥 Commits

Reviewing files that changed from the base of the PR and between 7e219be and b89473c.

📒 Files selected for processing (16)

• cypher/models/cypher/model.go
• cypher/models/pgsql/optimize/direction.go
• cypher/models/pgsql/optimize/optimizer.go
• cypher/models/pgsql/optimize/optimizer_test.go
• cypher/models/pgsql/optimize/reordering.go
• cypher/models/pgsql/test/translation_cases/multipart.sql
• cypher/models/pgsql/test/translation_cases/pattern_binding.sql
• cypher/models/pgsql/test/translation_cases/pattern_expansion.sql
• cypher/models/pgsql/translate/expansion.go
• cypher/models/pgsql/translate/model.go
• cypher/models/pgsql/translate/optimizer_safety_test.go
• cypher/models/pgsql/translate/path_functions.go
• cypher/models/pgsql/translate/pattern.go
• cypher/models/pgsql/translate/projection.go
• cypher/models/pgsql/translate/tracking.go
• cypher/models/pgsql/translate/traversal.go

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch BED-8779

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