perf(memory): add expires_at to semantic cache index composite (#2030)#2042
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perf(memory): add expires_at to semantic cache index composite (#2030)#2042
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The partial index idx_response_cache_semantic previously covered (embedding_model, embedding_ts DESC) but not expires_at. This caused get_semantic() to post-filter expired rows from the heap after index scan, rather than excluding them within the index traversal. Migration 038 recreates the index with expires_at as the second column, following the canonical equality-range-sort B-tree pattern. Query plan test validates the optimizer chooses the new index for the exact get_semantic() predicates. Fixes #2030. No application code changes, index-only optimization.
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Summary
Fixes issue #2030: The partial index
idx_response_cache_semanticon the semantic response cache table was missing theexpires_atcolumn. This causedget_semantic()queries to post-filter expired rows from the heap after matching by embedding, rather than excluding them during index traversal.Changes
idx_response_cache_semanticwithexpires_atas the second column, following the canonical equality-range-sort B-tree pattern:(embedding_model, expires_at, embedding_ts DESC) WHERE embedding IS NOT NULLtest_semantic_query_uses_composite_indexto validate EXPLAIN QUERY PLAN uses the new indexDesign & Validation
Technical Details
No functional changes, pure performance optimization.