branch-4.1: [codex] fix ANN OpenMP build budget and add concurrency test #61313#61652
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yiguolei merged 1 commit intobranch-4.1from Mar 24, 2026
Merged
branch-4.1: [codex] fix ANN OpenMP build budget and add concurrency test #61313#61652yiguolei merged 1 commit intobranch-4.1from
yiguolei merged 1 commit intobranch-4.1from
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## Summary This PR fixes ANN index build OpenMP thread budgeting and adds a BE unit test for the concurrency cap. ## Problem `ScopedOmpThreadBudget` computed available budget from `config::omp_threads_limit` directly. With the default `omp_threads_limit = -1`, each builder effectively reserved 1 thread and did not follow the documented auto behavior (80% of CPU cores). In addition, concurrent builders could overrun the intended global limit because there was no wait/coordination when the budget was exhausted. ## Root Cause In `faiss_ann_index.cpp`: - The constructor used `config::omp_threads_limit` directly instead of the auto-resolved limit from `get_omp_threads_limit()`. - No blocking mechanism existed when all OpenMP budget was already in use. ## Fix - Use `get_omp_threads_limit()` as the actual global limit for budgeting. - Add a condition variable to block builders until at least one OpenMP slot is available. - Keep the existing policy of reserving up to half of remaining budget (minimum 1). - Add concise comments to explain wait/wakeup behavior. ## Test - Added `VectorSearchTest.OmpThreadBudgetNeverExceedsLimit` in `be/test/storage/index/ann/faiss_vector_index_test.cpp`. - The test sets `config::omp_threads_limit = 1`, runs multiple concurrent ANN `add()` builds, samples `ann_index_build_index_threads`, and asserts peak usage never exceeds 1 and finally returns to 0. ## Validation - Local compilation/test run was intentionally skipped per request.
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yiguolei
approved these changes
Mar 24, 2026
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Cherry-picked from #61313