v1.0.28 CALL... UNION performance

[v1.0.28] - 2026-03-23

Added

• Vector query embedding cache for Cypher procedures:
  • added executor-level embedding-result caching for db.index.vector.queryNodes / compatibility vector query paths when the query input is text
  • added in-flight de-duplication for concurrent identical embed requests so the same query text is embedded once and shared across waiters.
  • what this means: repeated semantic/vector query calls spend less time in embedding and create fewer duplicate embedding workloads under concurrent traffic.

Changed

• Correlated subquery execution optimizations:
  • restored safe UNION fast paths in correlated MATCH ... CALL { ... UNION ... } ... execution with strict guards for write-safety and variable-dependency correctness
  • improved correlated seed extraction and batched lookup handling in subquery execution hot paths.
  • what this means: lower fixed-cost overhead for common correlated subquery/UNION shapes while preserving Neo4j-compatible semantics.
• Query cache key normalization performance:
  • replaced allocation-heavy whitespace normalization (strings.Fields join) with a single-pass compaction strategy.
  • what this means: fewer cache-key allocations and reduced GC pressure on read-heavy workloads.
• Traversal optimization safety hardening:
  • strengthened fallback start-node pruning behavior to fail open and preserve deterministic traversal semantics for chained/complex patterns.
  • what this means: traversal optimizations remain active without sacrificing correctness on multi-segment graph patterns.

Fixed

• UNION/subquery fixed-cost overhead in hot Cypher paths:
  • reduced allocation-heavy row dedupe and subquery processing overhead for CALL/UNION shapes.
• Correlated CALL + UNION semantics in mixed query shapes:
  • fixed guarded fast-path routing to keep duplicate-row and chained-traversal result behavior consistent while optimized execution is enabled.

Tests

• Added/expanded benchmark and regression coverage for:
  • correlated subquery + UNION fixed-cost cache-miss profiling
  • real-data Cypher/fabric-style e2e benchmark harnesses
  • traversal optional/WHERE pruning safety behavior
  • vector procedure caching behavior and compatibility paths.

Technical Details

• Range covered: v1.0.27..HEAD
• Commits in range: 1 (non-merge)
• Repository delta: 13 files changed, +1,754 / -86 lines
• Non-test surface changed: 8 files
• Primary focus areas: Cypher hot-path latency, allocation/GC reduction, correlated subquery/UNION execution, and vector query embed caching.