Bugfix for issue 33; reduce lock contention in Get(), parallel benchmarks.

- Fix for issue 33 (non-null-terminated result from
  leveldb_property_value())

- Support for running multiple instances of a benchmark in parallel.

- Reduce lock contention on Get():
  (1) Do not hold the lock while searching memtables.
  (2) Shard block and table caches 16-ways.

  Benchmark for evaluating this change:
  $ db_bench --benchmarks=fillseq1,readrandom --threads=$n
  (fillseq1 is a small hack to make sure fillseq runs once regardless
  of number of threads specified on the command line).



git-svn-id: https://leveldb.googlecode.com/svn/trunk@49 62dab493-f737-651d-591e-8d6aee1b9529

util/cache_test.cc

@@ -32,7 +32,7 @@ class CacheTest {
     current_->deleted_values_.push_back(DecodeValue(v));
   }
 
-  static const int kCacheSize = 100;
+  static const int kCacheSize = 1000;
   std::vector<int> deleted_keys_;
   std::vector<int> deleted_values_;
   Cache* cache_;
@@ -137,23 +137,40 @@ TEST(CacheTest, EvictionPolicy) {
   Insert(200, 201);
 
   // Frequently used entry must be kept around
-  for (int i = 0; i < kCacheSize; i++) {
+  for (int i = 0; i < kCacheSize + 100; i++) {
     Insert(1000+i, 2000+i);
     ASSERT_EQ(2000+i, Lookup(1000+i));
     ASSERT_EQ(101, Lookup(100));
   }
   ASSERT_EQ(101, Lookup(100));
-  ASSERT_EQ(2, deleted_keys_.size());
-  ASSERT_EQ(200, deleted_keys_[0]);
-  ASSERT_EQ(201, deleted_values_[0]);
+  ASSERT_EQ(-1, Lookup(200));
 }
 
-TEST(CacheTest, HeavyEntry) {
-  Insert(100, 101);
-  Insert(200, 201, kCacheSize);
-  ASSERT_EQ(1, deleted_keys_.size());
-  ASSERT_EQ(100, deleted_keys_[0]);
-  ASSERT_EQ(101, deleted_values_[0]);
+TEST(CacheTest, HeavyEntries) {
+  // Add a bunch of light and heavy entries and then count the combined
+  // size of items still in the cache, which must be approximately the
+  // same as the total capacity.
+  const int kLight = 1;
+  const int kHeavy = 10;
+  int added = 0;
+  int index = 0;
+  while (added < 2*kCacheSize) {
+    const int weight = (index & 1) ? kLight : kHeavy;
+    Insert(index, 1000+index, weight);
+    added += weight;
+    index++;
+  }
+
+  int cached_weight = 0;
+  for (int i = 0; i < index; i++) {
+    const int weight = (i & 1 ? kLight : kHeavy);
+    int r = Lookup(i);
+    if (r >= 0) {
+      cached_weight += weight;
+      ASSERT_EQ(1000+i, r);
+    }
+  }
+  ASSERT_LE(cached_weight, kCacheSize + kCacheSize/10);
 }
 
 TEST(CacheTest, NewId) {