Multi-poll backend optimization: configure CURLMOPT_MAXCONNECTS to avoid unnecessary TCP/TLS handshakes - #1034
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August 14, 2026 20:49
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| { | ||
| if (!max_concurrent_requests.has_value()) { return std::nullopt; } | ||
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| // libcurl documents this option as taking a `long`, and the value is internally store as an |
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| // libcurl documents this option as taking a `long`, and the value is internally store as an | |
| // libcurl documents this option as taking a `long`, and the value is internally stored as an |
| std::numeric_limits<std::size_t>::max() / 2, | ||
| static_cast<std::size_t>(limit), | ||
| static_cast<std::size_t>(limit) / 2 + 1}; | ||
| for (const auto ceiling : ceilings) { |
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| for (const auto ceiling : ceilings) { | |
| for (auto const ceiling : ceilings) { |
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By default libcurl sets
CURLMOPT_MAXCONNECTSto 4 x the number of easy handles attached to a multi handle. This is recomputed on every transition, and a transient dip in concurrency will cause libcurl to evict warm, reusable connections, and cause unnecessary TCP/TLS handshake. In this PR we pinCURLMOPT_MAXCONNECTSto a fixed size to avoid this problem.Benchmark on cudf-polars TPC-H SF-1K query 5 shows that, on
mainthe TCP connection opened is 618, whereas with this PR, the connection number drops to 496, which is a ~20% saving.