Start versions at zero in fuzz test for now

Also remove oldestVersion arg in write call tree

CMakeLists.txt

@@ -59,10 +59,6 @@ cmake_pop_check_state()
 
 option(USE_SIMD_FALLBACK
        "Use fallback implementations of functions that use SIMD" OFF)
-option(
-  USE_32_BIT_VERSIONS
-  "Store 32 bit versions internally, and rely on versions never being different by more than 2e9"
-  OFF)
 
 # This is encouraged according to
 # https://valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.clientreq
@@ -107,10 +103,6 @@ if(NOT USE_SIMD_FALLBACK)
   endif()
 endif()
 
-if(USE_32_BIT_VERSIONS)
-  add_compile_definitions(INTERNAL_VERSION_32_BIT=1)
-endif()
-
 set(CMAKE_CXX_IMPLICIT_LINK_LIBRARIES "")
 
 add_library(${PROJECT_NAME}-object OBJECT ConflictSet.cpp)

ConflictSet.cpp

@@ -78,18 +78,18 @@ constexpr void removeKey(struct Node *) {}
 
 // ==================== BEGIN IMPLEMENTATION ====================
 
-#ifndef INTERNAL_VERSION_32_BIT
+constexpr int64_t kNominalVersionWindow = 2e9;
-#define INTERNAL_VERSION_32_BIT 0
+constexpr int64_t kMaxCorrectVersionWindow =
-#endif
+    std::numeric_limits<int32_t>::max();
+static_assert(kNominalVersionWindow <= kMaxCorrectVersionWindow);
 
-#if INTERNAL_VERSION_32_BIT
 struct InternalVersionT {
   constexpr InternalVersionT() = default;
   constexpr explicit InternalVersionT(int64_t value) : value(value) {}
   constexpr int64_t toInt64() const { return value; } // GCOVR_EXCL_LINE
   constexpr auto operator<=>(const InternalVersionT &rhs) const {
     // Maintains ordering after overflow, as long as the full-precision versions
-    // are within ~2e9 of eachother.
+    // are within `kMaxCorrectVersionWindow` of eachother.
     return int32_t(value - rhs.value) <=> 0;
   }
   constexpr bool operator==(const InternalVersionT &) const = default;
@@ -99,20 +99,6 @@ private:
   uint32_t value;
 };
 thread_local InternalVersionT InternalVersionT::zero;
-#else
-struct InternalVersionT {
-  constexpr InternalVersionT() = default;
-  constexpr explicit InternalVersionT(int64_t value) : value(value) {}
-  constexpr int64_t toInt64() const { return value; } // GCOVR_EXCL_LINE
-  constexpr auto operator<=>(const InternalVersionT &rhs) const = default;
-  constexpr bool operator==(const InternalVersionT &) const = default;
-  static const InternalVersionT zero;
-
-private:
-  int64_t value;
-};
-const InternalVersionT InternalVersionT::zero{0};
-#endif
 
 struct Entry {
   InternalVersionT pointVersion;
@@ -527,13 +513,8 @@ std::string getSearchPath(Node *n);
 // Each node with an entry present gets a budget of kBytesPerKey. Node0 always
 // has an entry present.
 // Induction hypothesis is that each node's surplus is >= kMinNodeSurplus
-#if INTERNAL_VERSION_32_BIT
 constexpr int kBytesPerKey = 112;
 constexpr int kMinNodeSurplus = 80;
-#else
-constexpr int kBytesPerKey = 144;
-constexpr int kMinNodeSurplus = 104;
-#endif
 constexpr int kMinChildrenNode3 = 2;
 constexpr int kMinChildrenNode16 = 4;
 constexpr int kMinChildrenNode48 = 17;
@@ -1230,6 +1211,53 @@ void maybeDecreaseCapacity(Node *&self, NodeAllocators *allocators,
   freeAndMakeCapacityAtLeast(self, maxCapacity, allocators, impl, false);
 }
 
+void rezero(Node *n, InternalVersionT z) {
+#if DEBUG_VERBOSE && !defined(NDEBUG)
+  fprintf(stderr, "rezero to %" PRId64 ": %s\n", z.toInt64(),
+          getSearchPathPrintable(n).c_str());
+#endif
+  if (n->entryPresent) {
+    n->entry.pointVersion = std::max(n->entry.pointVersion, z);
+    n->entry.rangeVersion = std::max(n->entry.rangeVersion, z);
+  }
+  switch (n->getType()) {
+  case Type_Node0: {
+  } break;
+  case Type_Node3: {
+    auto *self = static_cast<Node3 *>(n);
+    for (int i = 0; i < 3; ++i) {
+      self->childMaxVersion[i] = std::max(self->childMaxVersion[i], z);
+    }
+  } break;
+  case Type_Node16: {
+    auto *self = static_cast<Node16 *>(n);
+    for (int i = 0; i < 16; ++i) {
+      self->childMaxVersion[i] = std::max(self->childMaxVersion[i], z);
+    }
+  } break;
+  case Type_Node48: {
+    auto *self = static_cast<Node48 *>(n);
+    for (int i = 0; i < 48; ++i) {
+      self->childMaxVersion[i] = std::max(self->childMaxVersion[i], z);
+    }
+    for (auto &m : self->maxOfMax) {
+      m = std::max(m, z);
+    }
+  } break;
+  case Type_Node256: {
+    auto *self = static_cast<Node256 *>(n);
+    for (int i = 0; i < 256; ++i) {
+      self->childMaxVersion[i] = std::max(self->childMaxVersion[i], z);
+    }
+    for (auto &m : self->maxOfMax) {
+      m = std::max(m, z);
+    }
+  } break;
+  default:                   // GCOVR_EXCL_LINE
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
+  }
+}
+
 void maybeDownsize(Node *self, NodeAllocators *allocators,
                    ConflictSet::Impl *impl, Node *&dontInvalidate) {
 
@@ -1281,6 +1309,9 @@ void maybeDownsize(Node *self, NodeAllocators *allocators,
       // Max versions are stored in the parent, so we need to update it now
       // that we have a new parent.
       setMaxVersion(child, impl, childMaxVersion);
+      if (child->parent) {
+        rezero(child->parent, InternalVersionT::zero);
+      }
 
       getInTree(self, impl) = child;
       allocators->node3.release(self3);
@@ -1323,7 +1354,7 @@ void maybeDownsize(Node *self, NodeAllocators *allocators,
 // the node after self. If erase invalidates the pointee of `dontInvalidate`, it
 // will update it to its new pointee as well.
 Node *erase(Node *self, NodeAllocators *allocators, ConflictSet::Impl *impl,
-            Node *&dontInvalidate) {
+            bool logical, Node *&dontInvalidate) {
   assert(self->parent != nullptr);
 
 #if DEBUG_VERBOSE && !defined(NDEBUG)
@@ -1333,7 +1364,7 @@ Node *erase(Node *self, NodeAllocators *allocators, ConflictSet::Impl *impl,
   Node *parent = self->parent;
   uint8_t parentsIndex = self->parentsIndex;
 
-  auto *result = nextLogical(self);
+  auto *result = logical ? nextLogical(self) : nextPhysical(self);
 
   removeKey(self);
   self->entryPresent = false;
@@ -1833,7 +1864,6 @@ bool scan16(const InternalVersionT *vs, const uint8_t *is, int begin, int end,
   uint64_t mask = vget_lane_u64(
       vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(results), 4)), 0);
 
-#if INTERNAL_VERSION_32_BIT
   uint32x4_t w4[4];
   memcpy(w4, vs, sizeof(w4));
   uint32_t rv;
@@ -1853,12 +1883,6 @@ bool scan16(const InternalVersionT *vs, const uint8_t *is, int begin, int end,
 
   uint64_t compared = vget_lane_u64(
       vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(combined), 4)), 0);
-#else
-  uint64_t compared = 0;
-  for (int i = 0; i < 16; ++i) {
-    compared |= uint64_t(vs[i] > readVersion) << (i << 2);
-  }
-#endif
 
   return !(compared & mask);
 
@@ -1871,17 +1895,11 @@ bool scan16(const InternalVersionT *vs, const uint8_t *is, int begin, int end,
       indices, _mm_max_epu8(indices, _mm_set1_epi8(end - begin))));
 
   uint32_t compared = 0;
-#if INTERNAL_VERSION_32_BIT
   if constexpr (kAVX512) {
     compared = compare16_32bit_avx512(vs, readVersion);
   } else {
     compared = compare16_32bit(vs, readVersion);
   }
-#else
-  for (int i = 0; i < 16; ++i) {
-    compared |= (vs[i] > readVersion) << i;
-  }
-#endif
   return !(compared & mask);
 
 #else
@@ -1914,7 +1932,7 @@ scan16(const InternalVersionT *vs, int begin, int end,
   assert(0 <= end && end <= 16);
   assert(begin <= end);
 
-#if INTERNAL_VERSION_32_BIT && defined(HAS_ARM_NEON)
+#if defined(HAS_ARM_NEON)
   uint32x4_t w4[4];
   memcpy(w4, vs, sizeof(w4));
   uint32_t rv;
@@ -1938,7 +1956,7 @@ scan16(const InternalVersionT *vs, int begin, int end,
   conflict &= end == 16 ? -1 : (uint64_t(1) << (end << 2)) - 1;
   conflict >>= begin << 2;
   return !conflict;
-#elif INTERNAL_VERSION_32_BIT && defined(HAS_AVX)
+#elif defined(HAS_AVX)
   uint32_t conflict;
   if constexpr (kAVX512) {
     conflict = compare16_32bit_avx512(vs, readVersion);
@@ -2678,9 +2696,9 @@ void destroyTree(Node *root) {
   }
 }
 
-void addPointWrite(Node *&root, InternalVersionT oldestVersion,
+void addPointWrite(Node *&root, std::span<const uint8_t> key,
-                   std::span<const uint8_t> key, InternalVersionT writeVersion,
+                   InternalVersionT writeVersion, NodeAllocators *allocators,
-                   NodeAllocators *allocators, ConflictSet::Impl *impl) {
+                   ConflictSet::Impl *impl) {
   auto *n = insert<true>(&root, key, writeVersion, allocators, impl);
   if (!n->entryPresent) {
     auto *p = nextLogical(n);
@@ -2691,24 +2709,23 @@ void addPointWrite(Node *&root, InternalVersionT oldestVersion,
     n->entry.pointVersion = writeVersion;
     setMaxVersion(n, impl, writeVersion);
     n->entry.rangeVersion =
-        p != nullptr ? p->entry.rangeVersion : oldestVersion;
+        p == nullptr ? InternalVersionT::zero
+                     : std::max(p->entry.rangeVersion, InternalVersionT::zero);
   } else {
     assert(writeVersion >= n->entry.pointVersion);
     n->entry.pointVersion = writeVersion;
   }
 }
 
-void addWriteRange(Node *&root, InternalVersionT oldestVersion,
+void addWriteRange(Node *&root, std::span<const uint8_t> begin,
-                   std::span<const uint8_t> begin, std::span<const uint8_t> end,
+                   std::span<const uint8_t> end, InternalVersionT writeVersion,
-                   InternalVersionT writeVersion, NodeAllocators *allocators,
+                   NodeAllocators *allocators, ConflictSet::Impl *impl) {
-                   ConflictSet::Impl *impl) {
 
   int lcp = longestCommonPrefix(begin.data(), end.data(),
                                 std::min(begin.size(), end.size()));
   if (lcp == int(begin.size()) && end.size() == begin.size() + 1 &&
       end.back() == 0) {
-    return addPointWrite(root, oldestVersion, begin, writeVersion, allocators,
+    return addPointWrite(root, begin, writeVersion, allocators, impl);
-                         impl);
   }
   const bool beginIsPrefix = lcp == int(begin.size());
   auto remaining = begin.subspan(0, lcp);
@@ -2756,7 +2773,8 @@ void addWriteRange(Node *&root, InternalVersionT oldestVersion,
   if (insertedBegin) {
     auto *p = nextLogical(beginNode);
     beginNode->entry.rangeVersion =
-        p != nullptr ? p->entry.rangeVersion : oldestVersion;
+        p == nullptr ? InternalVersionT::zero
+                     : std::max(p->entry.rangeVersion, InternalVersionT::zero);
     beginNode->entry.pointVersion = writeVersion;
     assert(maxVersion(beginNode, impl) <= writeVersion);
     setMaxVersion(beginNode, impl, writeVersion);
@@ -2775,7 +2793,8 @@ void addWriteRange(Node *&root, InternalVersionT oldestVersion,
   if (insertedEnd) {
     auto *p = nextLogical(endNode);
     endNode->entry.pointVersion =
-        p != nullptr ? p->entry.rangeVersion : oldestVersion;
+        p == nullptr ? InternalVersionT::zero
+                     : std::max(p->entry.rangeVersion, InternalVersionT::zero);
     auto m = maxVersion(endNode, impl);
     setMaxVersion(endNode, impl,
                   std::max<InternalVersionT>(m, endNode->entry.pointVersion));
@@ -2790,21 +2809,16 @@ void addWriteRange(Node *&root, InternalVersionT oldestVersion,
   }
 
   for (beginNode = nextLogical(beginNode); beginNode != endNode;
-       beginNode = erase(beginNode, allocators, impl, endNode)) {
+       beginNode =
+           erase(beginNode, allocators, impl, /*logical*/ true, endNode)) {
   }
 }
 
-Iterator firstGeq(Node *n, const std::span<const uint8_t> key) {
+Node *firstGeqPhysical(Node *n, const std::span<const uint8_t> key) {
   auto remaining = key;
   for (;;) {
     if (remaining.size() == 0) {
-      if (n->entryPresent) {
+      return n;
-        return {n, 0};
-      }
-      int c = getChildGeq(n, 0);
-      assert(c >= 0);
-      n = getChildExists(n, c);
-      goto downLeftSpine;
     }
 
     auto *child = getChild(n, remaining[0]);
@@ -2812,7 +2826,7 @@ Iterator firstGeq(Node *n, const std::span<const uint8_t> key) {
       int c = getChildGeq(n, remaining[0]);
       if (c >= 0) {
         n = getChildExists(n, c);
-        goto downLeftSpine;
+        return n;
       } else {
         n = nextSibling(n);
         if (n == nullptr) {
@@ -2820,9 +2834,9 @@ Iterator firstGeq(Node *n, const std::span<const uint8_t> key) {
           //  final library, since we can't remove a key without introducing a
           //  key after it, and the only production caller of firstGeq is for
           //  resuming the setOldestVersion scan.
-          return {nullptr, 1}; // GCOVR_EXCL_LINE
+          return nullptr; // GCOVR_EXCL_LINE
         }
-        goto downLeftSpine;
+        return n;
       }
     }
 
@@ -2835,10 +2849,10 @@ Iterator firstGeq(Node *n, const std::span<const uint8_t> key) {
       if (i < commonLen) {
         auto c = n->partialKey()[i] <=> remaining[i];
         if (c > 0) {
-          goto downLeftSpine;
+          return n;
         } else {
           n = nextSibling(n);
-          goto downLeftSpine;
+          return n;
         }
       }
       if (commonLen == n->partialKeyLen) {
@@ -2847,19 +2861,10 @@ Iterator firstGeq(Node *n, const std::span<const uint8_t> key) {
       } else if (n->partialKeyLen > int(remaining.size())) {
         // n is the first physical node greater than remaining, and there's no
         // eq node
-        goto downLeftSpine;
+        return n;
       }
     }
   }
-downLeftSpine:
-  for (;;) {
-    if (n->entryPresent) {
-      return {n, 1};
-    }
-    int c = getChildGeq(n, 0);
-    assert(c >= 0);
-    n = getChildExists(n, c);
-  }
 }
 
 struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
@@ -2870,8 +2875,9 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
       auto begin = std::span<const uint8_t>(r.begin.p, r.begin.len);
       auto end = std::span<const uint8_t>(r.end.p, r.end.len);
       result[i] =
-          InternalVersionT(reads[i].readVersion) < oldestVersion ||
+          reads[i].readVersion < oldestVersionFullPrecision ||
-                  reads[i].readVersion < newestVersionFullPrecision - 2e9
+                  reads[i].readVersion <
+                      newestVersionFullPrecision - kNominalVersionWindow
               ? TooOld
           : (end.size() > 0
                  ? checkRangeRead(root, begin, end,
@@ -2885,50 +2891,49 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
 
   void addWrites(const WriteRange *writes, int count, int64_t writeVersion) {
     assert(writeVersion >= newestVersionFullPrecision);
+
+    // TODO allow this condition
+    assert(writeVersion < newestVersionFullPrecision + kNominalVersionWindow);
+
     newestVersionFullPrecision = writeVersion;
-#if INTERNAL_VERSION_32_BIT
+    setOldestVersion(
-    InternalVersionT::zero = oldestVersion;
+        std::max(oldestVersionFullPrecision,
-#endif
+                 newestVersionFullPrecision - kNominalVersionWindow));
+    while (oldestExtantVersion <
+           newestVersionFullPrecision - kMaxCorrectVersionWindow) {
+      gcScanStep(1000);
+    }
+
     for (int i = 0; i < count; ++i) {
       const auto &w = writes[i];
       auto begin = std::span<const uint8_t>(w.begin.p, w.begin.len);
       auto end = std::span<const uint8_t>(w.end.p, w.end.len);
       if (w.end.len > 0) {
         keyUpdates += 3;
-        addWriteRange(root, oldestVersion, begin, end,
+        addWriteRange(root, begin, end, InternalVersionT(writeVersion),
-                      InternalVersionT(writeVersion), &allocators, this);
+                      &allocators, this);
       } else {
         keyUpdates += 2;
-        addPointWrite(root, oldestVersion, begin,
+        addPointWrite(root, begin, InternalVersionT(writeVersion), &allocators,
-                      InternalVersionT(writeVersion), &allocators, this);
+                      this);
       }
     }
   }
 
-  void setOldestVersion(int64_t o) {
+  // Spends up to `fuel` gc'ing, and returns its unused fuel. Reclaims memory
-    InternalVersionT oldestVersion{o};
+  // and updates oldestExtantVersion after spending enough fuel.
-    assert(o >= oldestVersionFullPrecision);
+  int64_t gcScanStep(int64_t fuel) {
-    this->oldestVersionFullPrecision = o;
+    Node *n = firstGeqPhysical(root, removalKey);
-    this->oldestVersion = oldestVersion;
-#if INTERNAL_VERSION_32_BIT
-    InternalVersionT::zero = oldestVersion;
-#endif
-#ifdef NDEBUG
-    // This is here for performance reasons, since we want to amortize the cost
-    // of storing the search path as a string. In tests, we want to exercise the
-    // rest of the code often.
-    if (keyUpdates < 100) {
-      return;
-    }
-#endif
-    Node *n = firstGeq(root, removalKey).n;
     // There's no way to erase removalKey without introducing a key after it
     assert(n != nullptr);
     // Don't erase the root
     if (n == root) {
+      rezero(n, oldestVersion);
+      rootMaxVersion = std::max(rootMaxVersion, oldestVersion);
       n = nextPhysical(n);
     }
-    for (; keyUpdates > 0 && n != nullptr; --keyUpdates) {
+    for (; fuel > 0 && n != nullptr; --fuel) {
+      rezero(n, oldestVersion);
       if (n->entryPresent && std::max(n->entry.pointVersion,
                                       n->entry.rangeVersion) <= oldestVersion) {
         // Any transaction n would have prevented from committing is
@@ -2938,7 +2943,7 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
         // node is greater than the point version of the left node
         assert(n->entry.rangeVersion <= oldestVersion);
         Node *dummy = nullptr;
-        n = erase(n, &allocators, this, dummy);
+        n = erase(n, &allocators, this, /*logical*/ false, dummy);
       } else {
         maybeDecreaseCapacity(n, &allocators, this);
         n = nextPhysical(n);
@@ -2946,14 +2951,44 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
     }
     if (n == nullptr) {
       removalKey = {};
+      oldestExtantVersion = oldestVersionAtGcBegin;
+      oldestVersionAtGcBegin = oldestVersionFullPrecision;
+#if DEBUG_VERBOSE && !defined(NDEBUG)
+      fprintf(stderr,
+              "new oldestExtantVersion: %" PRId64
+              ", new oldestVersionAtGcBegin: %" PRId64 "\n",
+              oldestExtantVersion, oldestVersionAtGcBegin);
+#endif
     } else {
       removalKeyArena = Arena();
       removalKey = getSearchPath(removalKeyArena, n);
     }
+    return fuel;
+  }
+
+  void setOldestVersion(int64_t o) {
+    if (o <= oldestVersionFullPrecision) {
+      return;
+    }
+    InternalVersionT oldestVersion{o};
+    this->oldestVersionFullPrecision = o;
+    this->oldestVersion = oldestVersion;
+    InternalVersionT::zero = oldestVersion;
+#ifdef NDEBUG
+    // This is here for performance reasons, since we want to amortize the cost
+    // of storing the search path as a string. In tests, we want to exercise the
+    // rest of the code often.
+    if (keyUpdates < 100) {
+      return;
+    }
+#endif
+    keyUpdates = gcScanStep(keyUpdates);
   }
 
   explicit Impl(int64_t oldestVersion)
       : oldestVersion(oldestVersion), oldestVersionFullPrecision(oldestVersion),
+        oldestExtantVersion(oldestVersion),
+        oldestVersionAtGcBegin(oldestVersion),
         newestVersionFullPrecision(oldestVersion) {
 #if DEBUG_VERBOSE
     fprintf(stderr, "radix_tree: create\n");
@@ -2972,6 +3007,8 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
     root->entryPresent = true;
     root->entry.pointVersion = this->oldestVersion;
     root->entry.rangeVersion = this->oldestVersion;
+
+    InternalVersionT::zero = this->oldestVersion;
   }
   ~Impl() {
 #if DEBUG_VERBOSE
@@ -2991,8 +3028,10 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
   InternalVersionT oldestVersion;
   // TODO this doesn't fully mitigate the 32-bit precision issue, since we still
   // need to make sure we clean up versions in the tree before they fall out of
-  // the 2e9 window.
+  // the `kMaxCorrectVersionWindow` window.
   int64_t oldestVersionFullPrecision;
+  int64_t oldestExtantVersion;
+  int64_t oldestVersionAtGcBegin;
   int64_t newestVersionFullPrecision;
   int64_t totalBytes = 0;
 };
@@ -3130,6 +3169,74 @@ int64_t internal_getBytes(ConflictSet::Impl *impl) { return impl->totalBytes; }
 
 // GCOVR_EXCL_START
 
+Iterator firstGeqLogical(Node *n, const std::span<const uint8_t> key) {
+  auto remaining = key;
+  for (;;) {
+    if (remaining.size() == 0) {
+      if (n->entryPresent) {
+        return {n, 0};
+      }
+      int c = getChildGeq(n, 0);
+      assert(c >= 0);
+      n = getChildExists(n, c);
+      goto downLeftSpine;
+    }
+
+    auto *child = getChild(n, remaining[0]);
+    if (child == nullptr) {
+      int c = getChildGeq(n, remaining[0]);
+      if (c >= 0) {
+        n = getChildExists(n, c);
+        goto downLeftSpine;
+      } else {
+        n = nextSibling(n);
+        if (n == nullptr) {
+          //  This line is genuinely unreachable from any entry point of the
+          //  final library, since we can't remove a key without introducing a
+          //  key after it, and the only production caller of firstGeq is for
+          //  resuming the setOldestVersion scan.
+          return {nullptr, 1}; // GCOVR_EXCL_LINE
+        }
+        goto downLeftSpine;
+      }
+    }
+
+    n = child;
+    remaining = remaining.subspan(1, remaining.size() - 1);
+
+    if (n->partialKeyLen > 0) {
+      int commonLen = std::min<int>(n->partialKeyLen, remaining.size());
+      int i = longestCommonPrefix(n->partialKey(), remaining.data(), commonLen);
+      if (i < commonLen) {
+        auto c = n->partialKey()[i] <=> remaining[i];
+        if (c > 0) {
+          goto downLeftSpine;
+        } else {
+          n = nextSibling(n);
+          goto downLeftSpine;
+        }
+      }
+      if (commonLen == n->partialKeyLen) {
+        // partial key matches
+        remaining = remaining.subspan(commonLen, remaining.size() - commonLen);
+      } else if (n->partialKeyLen > int(remaining.size())) {
+        // n is the first physical node greater than remaining, and there's no
+        // eq node
+        goto downLeftSpine;
+      }
+    }
+  }
+downLeftSpine:
+  for (;;) {
+    if (n->entryPresent) {
+      return {n, 1};
+    }
+    int c = getChildGeq(n, 0);
+    assert(c >= 0);
+    n = getChildExists(n, c);
+  }
+}
+
 void ConflictSet::check(const ReadRange *reads, Result *results,
                         int count) const {
   internal_check(impl, reads, results, count);
@@ -3326,14 +3433,60 @@ void checkParentPointers(Node *node, bool &success) {
 }
 
 Iterator firstGeq(Node *n, std::string_view key) {
-  return firstGeq(
+  return firstGeqLogical(
       n, std::span<const uint8_t>((const uint8_t *)key.data(), key.size()));
 }
 
+void checkVersionsGeqOldestExtant(Node *n,
+                                  InternalVersionT oldestExtantVersion) {
+  if (n->entryPresent) {
+    assert(n->entry.pointVersion >= oldestExtantVersion);
+    assert(n->entry.rangeVersion >= oldestExtantVersion);
+  }
+  switch (n->getType()) {
+  case Type_Node0: {
+  } break;
+  case Type_Node3: {
+    auto *self = static_cast<Node3 *>(n);
+    for (int i = 0; i < 3; ++i) {
+      assert(self->childMaxVersion[i] >= oldestExtantVersion);
+    }
+  } break;
+  case Type_Node16: {
+    auto *self = static_cast<Node16 *>(n);
+    for (int i = 0; i < 16; ++i) {
+      assert(self->childMaxVersion[i] >= oldestExtantVersion);
+    }
+  } break;
+  case Type_Node48: {
+    auto *self = static_cast<Node48 *>(n);
+    for (int i = 0; i < 48; ++i) {
+      assert(self->childMaxVersion[i] >= oldestExtantVersion);
+    }
+    for (auto m : self->maxOfMax) {
+      assert(m >= oldestExtantVersion);
+    }
+  } break;
+  case Type_Node256: {
+    auto *self = static_cast<Node256 *>(n);
+    for (int i = 0; i < 256; ++i) {
+      assert(self->childMaxVersion[i] >= oldestExtantVersion);
+    }
+    for (auto m : self->maxOfMax) {
+      assert(m >= oldestExtantVersion);
+    }
+  } break;
+  default:                   // GCOVR_EXCL_LINE
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
+  }
+}
+
 [[maybe_unused]] InternalVersionT
 checkMaxVersion(Node *root, Node *node, InternalVersionT oldestVersion,
                 bool &success, ConflictSet::Impl *impl) {
-  InternalVersionT expected{0};
+  checkVersionsGeqOldestExtant(node,
+                               InternalVersionT(impl->oldestExtantVersion));
+  auto expected = InternalVersionT::zero;
   if (node->entryPresent) {
     expected = std::max(expected, node->entry.pointVersion);
   }

Internal.h

@@ -467,13 +467,15 @@ inline uint32_t Arbitrary::bounded(uint32_t s) {
 // ==================== END ARBITRARY IMPL ====================
 
 struct ReferenceImpl {
-  explicit ReferenceImpl(int64_t oldestVersion) : oldestVersion(oldestVersion) {
+  explicit ReferenceImpl(int64_t oldestVersion)
+      : oldestVersion(oldestVersion), newestVersion(oldestVersion) {
     writeVersionMap[""] = oldestVersion;
   }
   void check(const ConflictSet::ReadRange *reads, ConflictSet::Result *results,
              int count) const {
     for (int i = 0; i < count; ++i) {
-      if (reads[i].readVersion < oldestVersion) {
+      if (reads[i].readVersion < oldestVersion ||
+          reads[i].readVersion < newestVersion - 2e9) {
         results[i] = ConflictSet::TooOld;
         continue;
       }
@@ -495,6 +497,8 @@ struct ReferenceImpl {
   }
   void addWrites(const ConflictSet::WriteRange *writes, int count,
                  int64_t writeVersion) {
+    assert(writeVersion >= newestVersion);
+    newestVersion = writeVersion;
     for (int i = 0; i < count; ++i) {
       auto begin =
           std::string((const char *)writes[i].begin.p, writes[i].begin.len);
@@ -519,6 +523,7 @@ struct ReferenceImpl {
   }
 
   int64_t oldestVersion;
+  int64_t newestVersion;
   std::map<std::string, int64_t> writeVersionMap;
 };
 
@@ -578,8 +583,8 @@ template <class ConflictSetImpl> struct TestDriver {
   explicit TestDriver(const uint8_t *data, size_t size)
       : arbitrary({data, size}) {}
 
-  int64_t oldestVersion = arbitrary.bounded(2) ? 0 : 0xfffffff0;
+  int64_t oldestVersion = 0;
-  int64_t writeVersion = oldestVersion + 100;
+  int64_t writeVersion = 0;
   ConflictSetImpl cs{oldestVersion};
   ReferenceImpl refImpl{oldestVersion};
 
@@ -600,7 +605,7 @@ template <class ConflictSetImpl> struct TestDriver {
     {
       int numPointWrites = arbitrary.bounded(100);
       int numRangeWrites = arbitrary.bounded(100);
-      int64_t v = (writeVersion += arbitrary.bounded(10));
+      int64_t v = (writeVersion += arbitrary.bounded(2e9));
       auto *writes =
           new (arena) ConflictSet::WriteRange[numPointWrites + numRangeWrites];
       auto keys = set<std::string_view>(arena);
@@ -642,18 +647,21 @@ template <class ConflictSetImpl> struct TestDriver {
         }
 #if DEBUG_VERBOSE && !defined(NDEBUG)
         if (writes[i].end.len == 0) {
-          fprintf(stderr, "Write: {%s} -> %" PRId64 "\n",
+          fprintf(stderr, "Write: {%s}\n", printable(writes[i].begin).c_str());
-                  printable(writes[i].begin).c_str(), writeVersion);
         } else {
-          fprintf(stderr, "Write: [%s, %s) -> %" PRId64 "\n",
+          fprintf(stderr, "Write: [%s, %s)\n",
                   printable(writes[i].begin).c_str(),
-                  printable(writes[i].end).c_str(), writeVersion);
+                  printable(writes[i].end).c_str());
         }
 #endif
       }
       assert(iter == keys.end());
       assert(i == numPointWrites + numRangeWrites);
 
+#if DEBUG_VERBOSE && !defined(NDEBUG)
+      fprintf(stderr, "Write @ %" PRId64 "\n", v);
+#endif
+
       CALLGRIND_START_INSTRUMENTATION;
       cs.addWrites(writes, numPointWrites + numRangeWrites, v);
       CALLGRIND_STOP_INSTRUMENTATION;
@@ -710,12 +718,12 @@ template <class ConflictSetImpl> struct TestDriver {
         reads[i].readVersion = v;
 #if DEBUG_VERBOSE && !defined(NDEBUG)
         if (reads[i].end.len == 0) {
-          fprintf(stderr, "Read: {%s} @ %d\n",
+          fprintf(stderr, "Read: {%s} @ %" PRId64 "\n",
-                  printable(reads[i].begin).c_str(), int(reads[i].readVersion));
+                  printable(reads[i].begin).c_str(), reads[i].readVersion);
         } else {
-          fprintf(stderr, "Read: [%s, %s) @ %d\n",
+          fprintf(stderr, "Read: [%s, %s) @ %" PRId64 "\n",
                   printable(reads[i].begin).c_str(),
-                  printable(reads[i].end).c_str(), int(reads[i].readVersion));
+                  printable(reads[i].end).c_str(), reads[i].readVersion);
         }
 #endif
       }