Revert "db/heat_load_balance: sort using an Nlog(N) algorithm"

This reverts commit b59c9ebd660f6ba4bec074c925c619ce68647331.

db/heat_load_balance.cc

@@ -285,18 +285,20 @@ redistribute(const std::vector<float>& p, unsigned me, unsigned k) {
         // We need a list of the mixed nodes sorted in increasing deficit order.
         // Actually, we only need to sort those nodes with deficit <=
         // min(deficit[me], mixed_surplus).
+        // TODO: use NlgN sort instead of this ridiculous N^2 implementation.
         // TODO: can we do this without a NlgN (although very small N, not even
         // the full rf)? Note also the distribution code below is N^2 anyway
         // (two nested for loops).
-        auto sorted_deficits = std::views::iota(0u, rf)
-            | std::views::filter([&](unsigned i) {
-                return deficit[i] && deficit[i] <= deficit[me] && deficit[i] < mixed_surplus;
-            })
-            | std::views::transform([&](unsigned i) {
-                return std::make_pair(i, deficit[i]);
-            })
-            | std::ranges::to<std::vector>();
-        std::ranges::sort(sorted_deficits, [](const auto& a, const auto& b) { return a.second < b.second; });
+        std::list<std::pair<unsigned, float>> sorted_deficits;
+        for (unsigned i = 0; i < rf; i++) {
+            if (deficit[i] && deficit[i] <= deficit[me] &&
+                    deficit[i] < mixed_surplus) {
+                auto it = sorted_deficits.begin();
+                while (it != sorted_deficits.end() && it->second < deficit[i])
+                    ++it;
+                sorted_deficits.insert(it, std::make_pair(i, deficit[i]));
+            }
+        }
         hr_logger.trace("sorted_deficits={}{}", sorted_deficits | std::views::keys, sorted_deficits | std::views::values);
         float s = 0;
         int count = mixed_count;