From dff976ec0af2684b821d72157da16fa1c86414e4 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <anoyes34@gmail.com>
Date: Thu, 18 Jan 2024 16:23:37 -0800
Subject: [PATCH] Shuffle keys before inserting

---
 ConflictSet.cpp | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 23eb785..fb967bd 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -3,13 +3,14 @@
 #include <cassert>
 #include <compare>
 #include <memory>
+#include <random>
 #include <span>
 #include <string_view>
 #include <utility>
 #include <vector>
 
-#define SHOW_PRIORITY 1
-#define DEBUG 1
+#define SHOW_PRIORITY 0
+#define DEBUG 0
 
 using Key = ConflictSet::Key;
 
@@ -527,6 +528,13 @@ struct ConflictSet::Impl {
 
     // TODO Descend until queries for front and back diverge
 
+    // Mitigate potential n^2 behavior of insertion by shuffling the insertion
+    // order. Not sure how this interacts with interleaved insertion but it's
+    // probably fine.
+    // TODO better/faster RNG?
+    std::mt19937 g(fastRand());
+    std::shuffle(stepwiseInserts.get(), stepwiseInserts.get() + count, g);
+
     runInterleaved(std::span<StepwiseInsert>(stepwiseInserts.get(), count));
 
     std::vector<Node *> workList;
@@ -538,6 +546,10 @@ struct ConflictSet::Impl {
     while (!workList.empty()) {
       Node *n = workList.back();
       workList.pop_back();
+#if DEBUG
+      fprintf(stderr, "\tcheck heap invariant %.*s\n", n->len,
+              (const char *)(n + 1));
+#endif
       if (n->parent == nullptr) {
         continue;
       }
@@ -561,8 +573,6 @@ struct ConflictSet::Impl {
         if (lr != nullptr) {
           workList.push_back(lr);
         }
-      } else {
-        continue;
       }
     }
   }
@@ -621,7 +631,7 @@ ConflictSet &ConflictSet::operator=(ConflictSet &&other) noexcept {
 int main(void) {
   int64_t writeVersion = 0;
   ConflictSet::Impl cs{writeVersion};
-  constexpr int kNumKeys = 3;
+  constexpr int kNumKeys = 5;
   ConflictSet::WriteRange write[kNumKeys];
   for (int i = 0; i < kNumKeys; ++i) {
     write[i].begin = toKey(i);