Fix MultiGet with PinnableSlices and Merge for WBWI (facebook#8299)

Summary:
The MultiGetFromBatchAndDB would fail if the PinnableSlice value being returned was pinned.  This could happen if the value was retrieved from the DB (not memtable) or potentially if the values were reused (and a previous iteration returned a slice that was pinned).

This change resets the pinnable value to clear it prior to attempting to use it, thereby eliminating the problem with the value already being pinned.

Pull Request resolved: facebook#8299

Reviewed By: jay-zhuang

Differential Revision: D28455426

Pulled By: mrambacher

fbshipit-source-id: a34d7d983ec9b6bb4c8a2b4892f72858d43e6972

utilities/write_batch_with_index/write_batch_with_index.cc

@@ -539,13 +539,15 @@ void WriteBatchWithIndex::MultiGetFromBatchAndDB(
   // after the transaction finishes.
   for (size_t i = 0; i < num_keys; ++i) {
     MergeContext merge_context;
-    PinnableSlice* pinnable_val = &values[i];
-    std::string& batch_value = *pinnable_val->GetSelf();
+    std::string batch_value;
     Status* s = &statuses[i];
+    PinnableSlice* pinnable_val = &values[i];
+    pinnable_val->Reset();
     auto result =
         wbwii.GetFromBatch(this, keys[i], &merge_context, &batch_value, s);
 
     if (result == WBWIIteratorImpl::kFound) {
+      *pinnable_val->GetSelf() = std::move(batch_value);
       pinnable_val->PinSelf();
       continue;
     }
@@ -581,15 +583,20 @@ void WriteBatchWithIndex::MultiGetFromBatchAndDB(
       std::pair<WBWIIteratorImpl::Result, MergeContext>& merge_result =
           merges[index];
       if (merge_result.first == WBWIIteratorImpl::kMergeInProgress) {
+        std::string merged_value;
         // Merge result from DB with merges in Batch
         if (key.s->ok()) {
           *key.s = wbwii.MergeKey(*key.key, iter->value, merge_result.second,
-                                  key.value->GetSelf());
+                                  &merged_value);
         } else {  // Key not present in db (s.IsNotFound())
           *key.s = wbwii.MergeKey(*key.key, nullptr, merge_result.second,
-                                  key.value->GetSelf());
+                                  &merged_value);
+        }
+        if (key.s->ok()) {
+          key.value->Reset();
+          *key.value->GetSelf() = std::move(merged_value);
+          key.value->PinSelf();
         }
-        key.value->PinSelf();
       }
     }
   }

utilities/write_batch_with_index/write_batch_with_index_internal.cc

@@ -621,8 +621,7 @@ WriteBatchWithIndexInternal::WriteBatchWithIndexInternal(
 Status WriteBatchWithIndexInternal::MergeKey(const Slice& key,
                                              const Slice* value,
                                              const MergeContext& context,
-                                             std::string* result,
-                                             Slice* result_operand) const {
+                                             std::string* result) const {
   if (column_family_ != nullptr) {
     auto cfh = static_cast_with_check<ColumnFamilyHandleImpl>(column_family_);
     const auto merge_operator = cfh->cfd()->ioptions()->merge_operator.get();
@@ -638,20 +637,20 @@ Status WriteBatchWithIndexInternal::MergeKey(const Slice& key,
       SystemClock* clock = immutable_db_options.clock;
       return MergeHelper::TimedFullMerge(merge_operator, key, value,
                                          context.GetOperands(), result, logger,
-                                         statistics, clock, result_operand);
+                                         statistics, clock);
     } else if (db_options_ != nullptr) {
       Statistics* statistics = db_options_->statistics.get();
       Env* env = db_options_->env;
       Logger* logger = db_options_->info_log.get();
       SystemClock* clock = env->GetSystemClock().get();
       return MergeHelper::TimedFullMerge(merge_operator, key, value,
                                          context.GetOperands(), result, logger,
-                                         statistics, clock, result_operand);
+                                         statistics, clock);
     } else {
       const auto cf_opts = cfh->cfd()->ioptions();
       return MergeHelper::TimedFullMerge(
           merge_operator, key, value, context.GetOperands(), result,
-          cf_opts->logger, cf_opts->stats, cf_opts->clock, result_operand);
+          cf_opts->logger, cf_opts->stats, cf_opts->clock);
     }
   } else {
     return Status::InvalidArgument("Must provide a column_family");

utilities/write_batch_with_index/write_batch_with_index_internal.h

@@ -306,13 +306,12 @@ class WriteBatchWithIndexInternal {
                                         const Slice& key,
                                         MergeContext* merge_context,
                                         std::string* value, Status* s);
-  Status MergeKey(const Slice& key, const Slice* value, std::string* result,
-                  Slice* result_operand = nullptr) const {
-    return MergeKey(key, value, merge_context_, result, result_operand);
+  Status MergeKey(const Slice& key, const Slice* value,
+                  std::string* result) const {
+    return MergeKey(key, value, merge_context_, result);
   }
   Status MergeKey(const Slice& key, const Slice* value,
-                  const MergeContext& context, std::string* result,
-                  Slice* result_operand = nullptr) const;
+                  const MergeContext& context, std::string* result) const;
   size_t GetNumOperands() const { return merge_context_.GetNumOperands(); }
   MergeContext* GetMergeContext() { return &merge_context_; }
   Slice GetOperand(int index) const { return merge_context_.GetOperand(index); }

utilities/write_batch_with_index/write_batch_with_index_test.cc

@@ -1412,6 +1412,49 @@ TEST_P(WriteBatchWithIndexTest, TestGetFromBatchAndDBMerge3) {
   ASSERT_EQ(value, "1,2");
 }
 
+TEST_P(WriteBatchWithIndexTest, TestPinnedGetFromBatchAndDB) {
+  Status s = OpenDB();
+  ASSERT_OK(s);
+
+  PinnableSlice value;
+
+  ASSERT_OK(db_->Put(write_opts_, "a", "a0"));
+  ASSERT_OK(db_->Put(write_opts_, "b", "b0"));
+  ASSERT_OK(db_->Merge(write_opts_, "b", "b1"));
+  ASSERT_OK(db_->Merge(write_opts_, "c", "c0"));
+  ASSERT_OK(db_->Merge(write_opts_, "d", "d0"));
+  ASSERT_OK(batch_->Merge("a", "a1"));
+  ASSERT_OK(batch_->Merge("a", "a2"));
+  ASSERT_OK(batch_->Merge("b", "b2"));
+  ASSERT_OK(batch_->Merge("d", "d1"));
+  ASSERT_OK(batch_->Merge("e", "e0"));
+
+  for (int i = 0; i < 2; i++) {
+    if (i == 1) {
+      // Do it again with a flushed DB...
+      ASSERT_OK(db_->Flush(FlushOptions(), db_->DefaultColumnFamily()));
+    }
+    ASSERT_OK(batch_->GetFromBatchAndDB(db_, read_opts_, "a", &value));
+    ASSERT_EQ("a0,a1,a2", value.ToString());
+
+    ASSERT_OK(batch_->GetFromBatchAndDB(db_, read_opts_, "b", &value));
+    ASSERT_EQ("b0,b1,b2", value.ToString());
+
+    ASSERT_OK(batch_->GetFromBatchAndDB(db_, read_opts_, "c", &value));
+    ASSERT_EQ("c0", value.ToString());
+
+    ASSERT_OK(batch_->GetFromBatchAndDB(db_, read_opts_, "d", &value));
+    ASSERT_EQ("d0,d1", value.ToString());
+
+    ASSERT_OK(batch_->GetFromBatchAndDB(db_, read_opts_, "e", &value));
+    ASSERT_EQ("e0", value.ToString());
+    ASSERT_OK(db_->Delete(write_opts_, "x"));
+
+    s = batch_->GetFromBatchAndDB(db_, read_opts_, "x", &value);
+    ASSERT_TRUE(s.IsNotFound());
+  }
+}
+
 void AssertKey(std::string key, WBWIIterator* iter) {
   ASSERT_TRUE(iter->Valid());
   ASSERT_EQ(key, iter->Entry().key.ToString());
@@ -1808,12 +1851,12 @@ TEST_P(WriteBatchWithIndexTest, MultiGetTest) {
   // Write some data to the db for the even numbered keys
   {
     WriteBatch wb;
-    for (size_t i = 1; i < keys.size(); ++i) {
+    for (size_t i = 0; i < keys.size(); i += 2) {
       std::string val = "val" + std::to_string(i);
       ASSERT_OK(wb.Put(cf0, keys[i], val));
     }
     ASSERT_OK(db_->Write(write_opts_, &wb));
-    for (size_t i = 1; i < keys.size(); ++i) {
+    for (size_t i = 0; i < keys.size(); i += 2) {
       std::string value;
       ASSERT_OK(db_->Get(read_opts_, cf0, keys[i], &value));
     }
@@ -1852,21 +1895,111 @@ TEST_P(WriteBatchWithIndexTest, MultiGetTest) {
       } else if ((i % 7) == 0) {  // Merge after Put
         std::string val = "new" + std::to_string(i);
         ASSERT_EQ(values[i], val + ",merge");
-      } else {
+      } else if ((i % 2) == 0) {
         std::string val = "val" + std::to_string(i);
         ASSERT_EQ(values[i], val + ",merge");
+      } else {
+        ASSERT_EQ(values[i], "merge");
       }
     } else if ((i % 5) == 0) {
       ASSERT_TRUE(statuses[i].IsNotFound());
     } else if ((i % 7) == 0) {
       ASSERT_OK(statuses[i]);
       ASSERT_EQ(values[i], "new" + std::to_string(i));
-    } else {
+    } else if ((i % 2) == 0) {
       ASSERT_OK(statuses[i]);
       ASSERT_EQ(values[i], "val" + std::to_string(i));
+    } else {
+      ASSERT_TRUE(statuses[i].IsNotFound());
     }
   }
 }
+TEST_P(WriteBatchWithIndexTest, MultiGetTest2) {
+  // MultiGet a lot of keys in order to force std::vector reallocations
+  const int num_keys = 700;
+  const int keys_per_pass = 100;
+  std::vector<std::string> keys;
+  for (size_t i = 0; i < num_keys; ++i) {
+    keys.emplace_back(std::to_string(i));
+  }
+  ASSERT_OK(OpenDB());
+  ColumnFamilyHandle* cf0 = db_->DefaultColumnFamily();
+
+  // Keys   0- 99 have a PUT in the batch but not DB
+  // Keys 100-199 have a PUT in the DB
+  // Keys 200-299 Have a PUT/DELETE
+  // Keys 300-399 Have a PUT/DELETE/MERGE
+  // Keys 400-499 have a PUT/MERGE
+  // Keys 500-599 have a MERGE only
+  // Keys 600-699 were never written
+  {
+    WriteBatch wb;
+    for (size_t i = 100; i < 500; i++) {
+      std::string val = std::to_string(i);
+      ASSERT_OK(wb.Put(cf0, keys[i], val));
+    }
+    ASSERT_OK(db_->Write(write_opts_, &wb));
+  }
+  ASSERT_OK(db_->Flush(FlushOptions(), cf0));
+  for (size_t i = 0; i < 100; i++) {
+    ASSERT_OK(batch_->Put(cf0, keys[i], keys[i]));
+  }
+  for (size_t i = 200; i < 400; i++) {
+    ASSERT_OK(batch_->Delete(cf0, keys[i]));
+  }
+  for (size_t i = 300; i < 600; i++) {
+    std::string val = std::to_string(i) + "m";
+    ASSERT_OK(batch_->Merge(cf0, keys[i], val));
+  }
+
+  Random rnd(301);
+  std::vector<PinnableSlice> values(keys_per_pass);
+  std::vector<Status> statuses(keys_per_pass);
+  for (int pass = 0; pass < 40; pass++) {
+    std::vector<Slice> key_slices;
+    for (size_t i = 0; i < keys_per_pass; i++) {
+      int random = rnd.Uniform(num_keys);
+      key_slices.emplace_back(keys[random]);
+    }
+    batch_->MultiGetFromBatchAndDB(db_, read_opts_, cf0, keys_per_pass,
+                                   key_slices.data(), values.data(),
+                                   statuses.data(), false);
+    for (size_t i = 0; i < keys_per_pass; i++) {
+      int key = ParseInt(key_slices[i].ToString());
+      switch (key / 100) {
+        case 0:  // 0-99 PUT only
+          ASSERT_OK(statuses[i]);
+          ASSERT_EQ(values[i], key_slices[i].ToString());
+          break;
+        case 1:  // 100-199 PUT only
+          ASSERT_OK(statuses[i]);
+          ASSERT_EQ(values[i], key_slices[i].ToString());
+          break;
+        case 2:  // 200-299 Deleted
+          ASSERT_TRUE(statuses[i].IsNotFound());
+          break;
+        case 3:  // 300-399 Delete+Merge
+          ASSERT_OK(statuses[i]);
+          ASSERT_EQ(values[i], key_slices[i].ToString() + "m");
+          break;
+        case 4:  // 400-400 Put+ Merge
+          ASSERT_OK(statuses[i]);
+          ASSERT_EQ(values[i], key_slices[i].ToString() + "," +
+                                   key_slices[i].ToString() + "m");
+          break;
+        case 5:  // Merge only
+          ASSERT_OK(statuses[i]);
+          ASSERT_EQ(values[i], key_slices[i].ToString() + "m");
+          break;
+        case 6:  // Never written
+          ASSERT_TRUE(statuses[i].IsNotFound());
+          break;
+        default:
+          assert(false);
+      }  // end switch
+    }    // End for each key
+  }      // end for passes
+}
 
 // This test has merges, but the merge does not play into the final result
 TEST_P(WriteBatchWithIndexTest, FakeMergeWithIteratorTest) {