scratch_defaults.hpp

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#pragma once
 
#include <pineforge/detail/scratch_errors.hpp>
#include <pineforge/detail/scratch_tables.hpp>
 
#include <cstddef>
#include <cstdint>
#include <limits>
 
namespace pineforge::detail {
 
// Physical resident rows <= 2x the rows kept at the last spill pass + 64
// (+ pinned rows); this is not a bound in terms of currently live rows.
// Admission still limits non-spillable cohort rows in the bounded scratch
// profile. This does not bound the number or heap size of pending orders.
inline constexpr std::size_t kMaxResidentCohorts = 4096;
 
// P0 is a POLICY admission tier, not a measured bound or a proof that a
// strategy fits. Counts include historical keys and internally generated
// successors. The finite-batch replacement reserve deliberately scales with
// input bars; actual exhaustion must fail, never grow or fall back to disk.
inline ScratchManifest default_scratch_manifest(std::uint64_t bars) {
    if (bars > std::numeric_limits<std::uint64_t>::max() / 2)
        throw ScratchCapacityError(ScratchResource::layout,
                                   "default scratch replacement reserve overflow");
    return {
        0, 0, // K_q/B_q retained in the descriptor; the q store is removed.
        262144, 25165824,
        32768, 4227072,
        65536, 4194304,
        27, 6912,
        2 * bars,
    };
}
 
// A stream without a declared lifetime bar count has its own fixed policy
// tier. A zero-bar finite batch remains distinct and admits zero roots.
inline ScratchManifest default_scratch_manifest() {
    auto manifest = default_scratch_manifest(0);
    manifest.R = 65536;
    return manifest;
}
 
} // namespace pineforge::detail