Don't count no prefix as Bloom hit (#10244)

Summary:
When a key is "out of domain" for the prefix_extractor (no
prefix assigned) then the Bloom filter is not queried. PerfContext
was counting this as a Bloom "hit" while Statistics doesn't count this
as a prefix Bloom checked. I think it's more accurate to call it neither
hit nor miss, so changing the counting to make it PerfContext coounting
more like Statistics.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10244

Test Plan:
tests updates and expanded (Get and MultiGet). Iterator test
coverage of the change will come in next PR

Reviewed By: bjlemaire

Differential Revision: D37371297

Pulled By: pdillinger

fbshipit-source-id: fed132fba6a92b2314ab898d449fce2d1586c157

db/db_basic_test.cc

@@ -2467,35 +2467,37 @@ TEST_P(MultiGetPrefixExtractorTest, Batched) {
   SetPerfLevel(kEnableCount);
   get_perf_context()->Reset();
 
-  // First key is not in the prefix_extractor domain
   ASSERT_OK(Put("k", "v0"));
   ASSERT_OK(Put("kk1", "v1"));
   ASSERT_OK(Put("kk2", "v2"));
   ASSERT_OK(Put("kk3", "v3"));
   ASSERT_OK(Put("kk4", "v4"));
-  std::vector<std::string> mem_keys(
+  std::vector<std::string> keys(
       {"k", "kk1", "kk2", "kk3", "kk4", "rofl", "lmho"});
-  std::vector<std::string> inmem_values;
-  inmem_values = MultiGet(mem_keys, nullptr);
-  ASSERT_EQ(inmem_values[0], "v0");
-  ASSERT_EQ(inmem_values[1], "v1");
-  ASSERT_EQ(inmem_values[2], "v2");
-  ASSERT_EQ(inmem_values[3], "v3");
-  ASSERT_EQ(inmem_values[4], "v4");
+  std::vector<std::string> expected(
+      {"v0", "v1", "v2", "v3", "v4", "NOT_FOUND", "NOT_FOUND"});
+  std::vector<std::string> values;
+  values = MultiGet(keys, nullptr);
+  ASSERT_EQ(values, expected);
+  // One key ("k") is not queried against the filter because it is outside
+  // the prefix_extractor domain, leaving 6 keys with queried prefixes.
   ASSERT_EQ(get_perf_context()->bloom_memtable_miss_count, 2);
-  ASSERT_EQ(get_perf_context()->bloom_memtable_hit_count, 5);
+  ASSERT_EQ(get_perf_context()->bloom_memtable_hit_count, 4);
   ASSERT_OK(Flush());
 
-  std::vector<std::string> keys({"k", "kk1", "kk2", "kk3", "kk4"});
-  std::vector<std::string> values;
   get_perf_context()->Reset();
   values = MultiGet(keys, nullptr);
-  ASSERT_EQ(values[0], "v0");
-  ASSERT_EQ(values[1], "v1");
-  ASSERT_EQ(values[2], "v2");
-  ASSERT_EQ(values[3], "v3");
-  ASSERT_EQ(values[4], "v4");
-  // Filter hits for 4 in-domain keys
+  ASSERT_EQ(values, expected);
+  ASSERT_EQ(get_perf_context()->bloom_sst_miss_count, 2);
+  ASSERT_EQ(get_perf_context()->bloom_sst_hit_count, 4);
+
+  // Also check Get stat
+  get_perf_context()->Reset();
+  for (size_t i = 0; i < keys.size(); ++i) {
+    values[i] = Get(keys[i]);
+  }
+  ASSERT_EQ(values, expected);
+  ASSERT_EQ(get_perf_context()->bloom_sst_miss_count, 2);
   ASSERT_EQ(get_perf_context()->bloom_sst_hit_count, 4);
 }
 

db/memtable.cc

@@ -334,8 +334,8 @@ class MemTableIterator : public InternalIterator {
       // iterator should only use prefix bloom filter
       auto ts_sz = comparator_.comparator.user_comparator()->timestamp_size();
       Slice user_k_without_ts(ExtractUserKeyAndStripTimestamp(k, ts_sz));
-      if (prefix_extractor_->InDomain(user_k_without_ts) &&
-          !bloom_->MayContain(
+      if (prefix_extractor_->InDomain(user_k_without_ts)) {
+        if (!bloom_->MayContain(
                 prefix_extractor_->Transform(user_k_without_ts))) {
           PERF_COUNTER_ADD(bloom_memtable_miss_count, 1);
           valid_ = false;
@@ -344,6 +344,7 @@ class MemTableIterator : public InternalIterator {
           PERF_COUNTER_ADD(bloom_memtable_hit_count, 1);
         }
       }
+    }
     iter_->Seek(k, nullptr);
     valid_ = iter_->Valid();
   }
@@ -353,8 +354,8 @@ class MemTableIterator : public InternalIterator {
     if (bloom_) {
       auto ts_sz = comparator_.comparator.user_comparator()->timestamp_size();
       Slice user_k_without_ts(ExtractUserKeyAndStripTimestamp(k, ts_sz));
-      if (prefix_extractor_->InDomain(user_k_without_ts) &&
-          !bloom_->MayContain(
+      if (prefix_extractor_->InDomain(user_k_without_ts)) {
+        if (!bloom_->MayContain(
                 prefix_extractor_->Transform(user_k_without_ts))) {
           PERF_COUNTER_ADD(bloom_memtable_miss_count, 1);
           valid_ = false;
@@ -363,6 +364,7 @@ class MemTableIterator : public InternalIterator {
           PERF_COUNTER_ADD(bloom_memtable_hit_count, 1);
         }
       }
+    }
     iter_->Seek(k, nullptr);
     valid_ = iter_->Valid();
     if (!Valid()) {
@@ -893,16 +895,20 @@ bool MemTable::Get(const LookupKey& key, std::string* value,
   bool may_contain = true;
   size_t ts_sz = GetInternalKeyComparator().user_comparator()->timestamp_size();
   Slice user_key_without_ts = StripTimestampFromUserKey(key.user_key(), ts_sz);
+  bool bloom_checked = false;
   if (bloom_filter_) {
     // when both memtable_whole_key_filtering and prefix_extractor_ are set,
     // only do whole key filtering for Get() to save CPU
     if (moptions_.memtable_whole_key_filtering) {
       may_contain = bloom_filter_->MayContain(user_key_without_ts);
+      bloom_checked = true;
     } else {
       assert(prefix_extractor_);
-      may_contain = !prefix_extractor_->InDomain(user_key_without_ts) ||
-                    bloom_filter_->MayContain(
+      if (prefix_extractor_->InDomain(user_key_without_ts)) {
+        may_contain = bloom_filter_->MayContain(
             prefix_extractor_->Transform(user_key_without_ts));
+        bloom_checked = true;
+      }
     }
   }
 
@@ -911,7 +917,7 @@ bool MemTable::Get(const LookupKey& key, std::string* value,
     PERF_COUNTER_ADD(bloom_memtable_miss_count, 1);
     *seq = kMaxSequenceNumber;
   } else {
-    if (bloom_filter_) {
+    if (bloom_checked) {
       PERF_COUNTER_ADD(bloom_memtable_hit_count, 1);
     }
     GetFromTable(key, *max_covering_tombstone_seq, do_merge, callback,
@@ -988,10 +994,6 @@ void MemTable::MultiGet(const ReadOptions& read_options, MultiGetRange* range,
         bloom_keys[num_keys] =
             prefix_extractor_->Transform(iter->ukey_without_ts);
         range_indexes[num_keys++] = iter.index();
-      } else {
-        // TODO: consider not counting these as Bloom hits to more closely
-        // match bloom_sst_hit_count
-        PERF_COUNTER_ADD(bloom_memtable_hit_count, 1);
       }
     }
     bloom_filter_->MayContain(num_keys, &bloom_keys[0], &may_match[0]);