"max of max" for Node48

ConflictSet.cpp

@@ -294,6 +294,8 @@ struct Node48 : Node {
   int8_t nextFree;
   int8_t index[256];
   Child children[kMaxNodes];
+  // Max of each "page" of 16 children
+  int64_t maxOfMax[16];
 
   uint8_t *partialKey() { return (uint8_t *)(this + 1); }
 
@@ -417,6 +419,7 @@ inline void Node48::copyChildrenAndKeyFrom(const Node16 &other) {
     children[i] = other.children[i];
     assert(children[i].child->parent == &other);
     children[i].child->parent = this;
+    maxOfMax[x >> 4] = std::max(maxOfMax[x >> 4], children[i].childMaxVersion);
     ++i;
   }
 }
@@ -431,6 +434,7 @@ inline void Node48::copyChildrenAndKeyFrom(const Node48 &other) {
     assert(children[i].child->parent == &other);
     children[i].child->parent = this;
   }
+  memcpy(maxOfMax, other.maxOfMax, sizeof(maxOfMax));
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
@@ -453,6 +457,7 @@ inline void Node48::copyChildrenAndKeyFrom(const Node256 &other) {
         ++i;
       },
       0, 256);
+  memcpy(maxOfMax, other.maxOfMax, sizeof(maxOfMax));
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
@@ -467,10 +472,9 @@ inline void Node256::copyChildrenAndKeyFrom(const Node48 &other) {
         children[c] = other.children[other.index[c]];
         assert(children[c].child->parent == &other);
         children[c].child->parent = this;
-        maxOfMax[c >> 4] =
-            std::max(maxOfMax[c >> 4], children[c].childMaxVersion);
       },
       0, 256);
+  memcpy(maxOfMax, other.maxOfMax, sizeof(maxOfMax));
   memcpy(partialKey(), &other + 1, partialKeyLen);
 }
 
@@ -571,7 +575,7 @@ template <class T> struct BoundedFreeListAllocator {
     if constexpr (!std::is_same_v<T, Node0>) {
       memset(result->children, 0, sizeof(result->children));
     }
-    if constexpr (std::is_same_v<T, Node256>) {
+    if constexpr (std::is_same_v<T, Node48> || std::is_same_v<T, Node256>) {
       memset(result->maxOfMax, 0, sizeof(result->maxOfMax));
     }
     return result;
@@ -1688,13 +1692,37 @@ bool checkMaxBetweenExclusive(Node *n, int begin, int end,
   } break;
   case Type_Node48: {
     auto *self = static_cast<Node48 *>(n);
+    // Check the first page
+    if (self->maxOfMax[begin >> 4] > readVersion) {
       bool result = true;
       self->bitSet.forEachInRange(
           [&](int i) {
             result &=
                 self->children[self->index[i]].childMaxVersion <= readVersion;
           },
-        begin, end);
+          begin, std::min((begin & ~15) + 16, end));
+      if (!result) {
+        return result;
+      }
+    }
+    // Check the last page
+    if (end >= 1 && self->maxOfMax[(end - 1) >> 4] > readVersion) {
+      bool result = true;
+      self->bitSet.forEachInRange(
+          [&](int i) {
+            result &=
+                self->children[self->index[i]].childMaxVersion <= readVersion;
+          },
+          std::max(begin, end & ~15), end);
+      if (!result) {
+        return result;
+      }
+    }
+    // Check inner pages
+    bool result = true;
+    for (int i = (begin >> 4) + 1; i < (end - 1) >> 4; ++i) {
+      result &= self->maxOfMax[i] <= readVersion;
+    }
     return result;
   }
   case Type_Node256: {
@@ -2656,6 +2684,7 @@ void setMaxVersion(Node *n, ConflictSet::Impl *impl, int64_t newMax) {
     auto *n48 = static_cast<Node48 *>(n);
     assert(n48->bitSet.test(index));
     n48->children[n48->index[index]].childMaxVersion = newMax;
+    n48->maxOfMax[index >> 4] = std::max(n48->maxOfMax[index >> 4], newMax);
     return;
   }
   case Type_Node256: {