Change server bench to point write heavy workload

Previously, with a finite set of keys, latest_extant_version could fall all the way behind so that a call to addWrites would have to do O(n) work eventually.

ConflictSet.cpp

@@ -4412,6 +4412,9 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
     assert(writeContext.accum.entries_erased == 0);
     assert(writeContext.accum.entries_inserted == 0);
 
+    // Queue up some gc work just for (potentially) increasing the version
+    ++keyUpdates;
+
     if (oldestExtantVersion < writeVersion - kMaxCorrectVersionWindow)
         [[unlikely]] {
       if (writeVersion > newestVersionFullPrecision + kNominalVersionWindow) {

ServerBench.cpp

@@ -1,5 +1,6 @@
 #include <atomic>
 #include <cstdint>
+#include <cstdlib>
 #include <errno.h>
 #include <netdb.h>
 #include <stdio.h>
@@ -37,41 +38,20 @@ std::string makeKey(int64_t num, int suffixLen) {
 
 void workload(weaselab::ConflictSet *cs) {
   int64_t version = kWindowSize;
-  for (int i = 0; i < kNumPrefixes; ++i) {
-    for (int j = 0; j < 50; ++j) {
-      weaselab::ConflictSet::WriteRange wr;
-      auto k = makeKey(i, j);
-      wr.begin.p = (const uint8_t *)k.data();
-      wr.begin.len = k.size();
-      wr.end.len = 0;
-      cs->addWrites(&wr, 1, version);
-    }
-  }
-  ++version;
-  for (int i = 0; i < kNumPrefixes; ++i) {
-    weaselab::ConflictSet::WriteRange wr;
-    auto k = makeKey(i, 50);
-    wr.begin.p = (const uint8_t *)k.data();
-    wr.begin.len = k.size();
-    wr.end.len = 0;
-    cs->addWrites(&wr, 1, version);
-  }
-
-  constexpr int kNumReads = 1;
-  std::vector<weaselab::ConflictSet::Result> results(kNumReads);
+  constexpr int kNumWrites = 16;
   for (;; transactions.fetch_add(1, std::memory_order_relaxed)) {
-    std::vector<std::string> keys(kNumReads);
-    for (auto &k : keys) {
-      k = makeKey(rand() % kNumPrefixes, 49);
+    std::vector<std::string> keys;
+    std::vector<weaselab::ConflictSet::WriteRange> writes;
+    for (int i = 0; i < kNumWrites; ++i) {
+      keys.push_back(makeKey(rand() % kNumPrefixes, rand() % 50));
     }
-    std::vector<weaselab::ConflictSet::ReadRange> reads(kNumReads);
-    for (int i = 0; i < reads.size(); ++i) {
-      reads[i].begin.p = (const uint8_t *)(keys[i].data());
-      reads[i].begin.len = keys[i].size();
-      reads[i].end.len = 0;
-      reads[i].readVersion = version - 1;
+    for (int i = 0; i < kNumWrites; ++i) {
+      writes.push_back({{(const uint8_t *)keys[i].data(), int(keys[i].size())},
+                        {nullptr, 0}});
     }
-    cs->check(reads.data(), results.data(), kNumReads);
+    cs->addWrites(writes.data(), writes.size(), version);
+    cs->setOldestVersion(version - kWindowSize);
+    ++version;
   }
 }