Adding GetApproximateMemTableStats method

Summary:
Added method that returns approx num of entries as well as size for memtables.
Closes https://github.com/facebook/rocksdb/pull/1841

Differential Revision: D4511990

Pulled By: VitaliyLi

fbshipit-source-id: 9a4576e

HISTORY.md

@@ -7,6 +7,7 @@
 * Added new overloaded function GetApproximateSizes that allows to specify if memtable stats should be computed only without computing SST files' stats approximations.
 * NewLRUCache() will determine number of shard bits automatically based on capacity, if the user doesn't pass one. This also impacts the default block cache when the user doesn't explict provide one.
 * Change the default of delayed slowdown value to 16MB/s and further increase the L0 stop condition to 36 files.
+* Added new function GetApproximateMemTableStats that approximates both number of records and size of memtables.
 
 ### Bug Fixes
 * Fix the bug that if 2PC is enabled, checkpoints may loss some recent transactions.

db/db_impl.cc

@@ -5558,6 +5558,28 @@ ColumnFamilyHandle* DBImpl::GetColumnFamilyHandle(uint32_t column_family_id) {
   return cf_memtables->GetColumnFamilyHandle();
 }
 
+void DBImpl::GetApproximateMemTableStats(ColumnFamilyHandle* column_family,
+                                         const Range& range,
+                                         uint64_t* const count,
+                                         uint64_t* const size) {
+  ColumnFamilyHandleImpl* cfh =
+      reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
+  ColumnFamilyData* cfd = cfh->cfd();
+  SuperVersion* sv = GetAndRefSuperVersion(cfd);
+
+  // Convert user_key into a corresponding internal key.
+  InternalKey k1(range.start, kMaxSequenceNumber, kValueTypeForSeek);
+  InternalKey k2(range.limit, kMaxSequenceNumber, kValueTypeForSeek);
+  MemTable::MemTableStats memStats =
+      sv->mem->ApproximateStats(k1.Encode(), k2.Encode());
+  MemTable::MemTableStats immStats =
+      sv->imm->ApproximateStats(k1.Encode(), k2.Encode());
+  *count = memStats.count + immStats.count;
+  *size = memStats.size + immStats.size;
+
+  ReturnAndCleanupSuperVersion(cfd, sv);
+}
+
 void DBImpl::GetApproximateSizes(ColumnFamilyHandle* column_family,
                                  const Range* range, int n, uint64_t* sizes,
                                  uint8_t include_flags) {
@@ -5578,8 +5600,8 @@ void DBImpl::GetApproximateSizes(ColumnFamilyHandle* column_family,
       sizes[i] += versions_->ApproximateSize(v, k1.Encode(), k2.Encode());
     }
     if (include_flags & DB::SizeApproximationFlags::INCLUDE_MEMTABLES) {
-      sizes[i] += sv->mem->ApproximateSize(k1.Encode(), k2.Encode());
-      sizes[i] += sv->imm->ApproximateSize(k1.Encode(), k2.Encode());
+      sizes[i] += sv->mem->ApproximateStats(k1.Encode(), k2.Encode()).size;
+      sizes[i] += sv->imm->ApproximateStats(k1.Encode(), k2.Encode()).size;
     }
   }
 

db/db_impl.h

@@ -140,6 +140,11 @@ class DBImpl : public DB {
                                    const Range* range, int n, uint64_t* sizes,
                                    uint8_t include_flags
                                    = INCLUDE_FILES) override;
+  using DB::GetApproximateMemTableStats;
+  virtual void GetApproximateMemTableStats(ColumnFamilyHandle* column_family,
+                                           const Range& range,
+                                           uint64_t* const count,
+                                           uint64_t* const size) override;
   using DB::CompactRange;
   virtual Status CompactRange(const CompactRangeOptions& options,
                               ColumnFamilyHandle* column_family,

db/db_test.cc

@@ -1497,6 +1497,59 @@ TEST_F(DBTest, ApproximateSizesMemTable) {
   ASSERT_GT(size_without_mt, 6000);
 }
 
+TEST_F(DBTest, GetApproximateMemTableStats) {
+  Options options = CurrentOptions();
+  options.write_buffer_size = 100000000;
+  options.compression = kNoCompression;
+  options.create_if_missing = true;
+  DestroyAndReopen(options);
+
+  const int N = 128;
+  Random rnd(301);
+  for (int i = 0; i < N; i++) {
+    ASSERT_OK(Put(Key(i), RandomString(&rnd, 1024)));
+  }
+
+  uint64_t count;
+  uint64_t size;
+
+  std::string start = Key(50);
+  std::string end = Key(60);
+  Range r(start, end);
+  db_->GetApproximateMemTableStats(r, &count, &size);
+  ASSERT_GT(count, 0);
+  ASSERT_LE(count, N);
+  ASSERT_GT(size, 6000);
+  ASSERT_LT(size, 204800);
+
+  start = Key(500);
+  end = Key(600);
+  r = Range(start, end);
+  db_->GetApproximateMemTableStats(r, &count, &size);
+  ASSERT_EQ(count, 0);
+  ASSERT_EQ(size, 0);
+
+  Flush();
+
+  start = Key(50);
+  end = Key(60);
+  r = Range(start, end);
+  db_->GetApproximateMemTableStats(r, &count, &size);
+  ASSERT_EQ(count, 0);
+  ASSERT_EQ(size, 0);
+
+  for (int i = 0; i < N; i++) {
+    ASSERT_OK(Put(Key(1000 + i), RandomString(&rnd, 1024)));
+  }
+
+  start = Key(100);
+  end = Key(1020);
+  r = Range(start, end);
+  db_->GetApproximateMemTableStats(r, &count, &size);
+  ASSERT_GT(count, 20);
+  ASSERT_GT(size, 6000);
+}
+
 TEST_F(DBTest, ApproximateSizes) {
   do {
     Options options = CurrentOptions();
@@ -2821,6 +2874,14 @@ class ModelDB : public DB {
       sizes[i] = 0;
     }
   }
+  using DB::GetApproximateMemTableStats;
+  virtual void GetApproximateMemTableStats(ColumnFamilyHandle* column_family,
+                                           const Range& range,
+                                           uint64_t* const count,
+                                           uint64_t* const size) override {
+    *count = 0;
+    *size = 0;
+  }
   using DB::CompactRange;
   virtual Status CompactRange(const CompactRangeOptions& options,
                               ColumnFamilyHandle* column_family,

db/memtable.cc

@@ -390,16 +390,16 @@ port::RWMutex* MemTable::GetLock(const Slice& key) {
   return &locks_[hash(key) % locks_.size()];
 }
 
-uint64_t MemTable::ApproximateSize(const Slice& start_ikey,
+MemTable::MemTableStats MemTable::ApproximateStats(const Slice& start_ikey,
                                                    const Slice& end_ikey) {
   uint64_t entry_count = table_->ApproximateNumEntries(start_ikey, end_ikey);
   entry_count += range_del_table_->ApproximateNumEntries(start_ikey, end_ikey);
   if (entry_count == 0) {
-    return 0;
+    return {0, 0};
   }
   uint64_t n = num_entries_.load(std::memory_order_relaxed);
   if (n == 0) {
-    return 0;
+    return {0, 0};
   }
   if (entry_count > n) {
     // (range_del_)table_->ApproximateNumEntries() is just an estimate so it can
@@ -408,7 +408,7 @@ uint64_t MemTable::ApproximateSize(const Slice& start_ikey,
     entry_count = n;
   }
   uint64_t data_size = data_size_.load(std::memory_order_relaxed);
-  return entry_count * (data_size / n);
+  return {entry_count * (data_size / n), entry_count};
 }
 
 void MemTable::Add(SequenceNumber s, ValueType type,

db/memtable.h

@@ -326,7 +326,13 @@ class MemTable {
     return table_->IsSnapshotSupported() && !moptions_.inplace_update_support;
   }
 
-  uint64_t ApproximateSize(const Slice& start_ikey, const Slice& end_ikey);
+  struct MemTableStats {
+    uint64_t size;
+    uint64_t count;
+  };
+
+  MemTableStats ApproximateStats(const Slice& start_ikey,
+                                 const Slice& end_ikey);
 
   // Get the lock associated for the key
   port::RWMutex* GetLock(const Slice& key);

db/memtable_list.cc

@@ -190,13 +190,15 @@ uint64_t MemTableListVersion::GetTotalNumEntries() const {
   return total_num;
 }
 
-uint64_t MemTableListVersion::ApproximateSize(const Slice& start_ikey,
-                                              const Slice& end_ikey) {
-  uint64_t total_size = 0;
+MemTable::MemTableStats MemTableListVersion::ApproximateStats(
+    const Slice& start_ikey, const Slice& end_ikey) {
+  MemTable::MemTableStats total_stats = {0, 0};
   for (auto& m : memlist_) {
-    total_size += m->ApproximateSize(start_ikey, end_ikey);
+    auto mStats = m->ApproximateStats(start_ikey, end_ikey);
+    total_stats.size += mStats.size;
+    total_stats.count += mStats.count;
   }
-  return total_size;
+  return total_stats;
 }
 
 uint64_t MemTableListVersion::GetTotalNumDeletes() const {

db/memtable_list.h

@@ -95,7 +95,8 @@ class MemTableListVersion {
 
   uint64_t GetTotalNumDeletes() const;
 
-  uint64_t ApproximateSize(const Slice& start_ikey, const Slice& end_ikey);
+  MemTable::MemTableStats ApproximateStats(const Slice& start_ikey,
+                                           const Slice& end_ikey);
 
   // Returns the value of MemTable::GetEarliestSequenceNumber() on the most
   // recent MemTable in this list or kMaxSequenceNumber if the list is empty.

include/rocksdb/db.h

@@ -616,6 +616,18 @@ class DB {
                         include_flags);
   }
 
+  // The method is similar to GetApproximateSizes, except it
+  // returns approximate number of records in memtables.
+  virtual void GetApproximateMemTableStats(ColumnFamilyHandle* column_family,
+                                           const Range& range,
+                                           uint64_t* const count,
+                                           uint64_t* const size) = 0;
+  virtual void GetApproximateMemTableStats(const Range& range,
+                                           uint64_t* const count,
+                                           uint64_t* const size) {
+    GetApproximateMemTableStats(DefaultColumnFamily(), range, count, size);
+  }
+
   // Deprecated versions of GetApproximateSizes
   ROCKSDB_DEPRECATED_FUNC virtual void GetApproximateSizes(
       const Range* range, int n, uint64_t* sizes,

include/rocksdb/utilities/stackable_db.h

@@ -167,6 +167,14 @@ class StackableDB : public DB {
                                     include_flags);
   }
 
+  using DB::GetApproximateMemTableStats;
+  virtual void GetApproximateMemTableStats(ColumnFamilyHandle* column_family,
+                                           const Range& range,
+                                           uint64_t* const count,
+                                           uint64_t* const size) override {
+    return db_->GetApproximateMemTableStats(column_family, range, count, size);
+  }
+
   using DB::CompactRange;
   virtual Status CompactRange(const CompactRangeOptions& options,
                               ColumnFamilyHandle* column_family,