Add a DB Property For Number of Deletions in Memtables

Summary: Add a DB property for number of deletions in memtables. It can sometimes help people debug slowness because of too many deletes.

Test Plan: Add test cases.

Reviewers: rven, yhchiang, kradhakrishnan, igor

Reviewed By: igor

Subscribers: leveldb, dhruba, yoshinorim

Differential Revision: https://reviews.facebook.net/D35247

db/db_test.cc

@@ -3059,6 +3059,35 @@ TEST_F(DBTest, NumImmutableMemTable) {
     // "200" is the size of the metadata of an empty skiplist, this would
     // break if we change the default skiplist implementation
     ASSERT_EQ(num, "200");
+
+    uint64_t int_num;
+    uint64_t base_total_size;
+    ASSERT_TRUE(dbfull()->GetIntProperty(
+        handles_[1], "rocksdb.estimate-num-keys", &base_total_size));
+
+    ASSERT_OK(dbfull()->Delete(writeOpt, handles_[1], "k2"));
+    ASSERT_OK(dbfull()->Put(writeOpt, handles_[1], "k3", ""));
+    ASSERT_OK(dbfull()->Delete(writeOpt, handles_[1], "k3"));
+    ASSERT_TRUE(dbfull()->GetIntProperty(
+        handles_[1], "rocksdb.num-deletes-active-mem-table", &int_num));
+    ASSERT_EQ(int_num, 2U);
+    ASSERT_TRUE(dbfull()->GetIntProperty(
+        handles_[1], "rocksdb.num-entries-active-mem-table", &int_num));
+    ASSERT_EQ(int_num, 3U);
+
+    ASSERT_OK(dbfull()->Put(writeOpt, handles_[1], "k2", big_value));
+    ASSERT_OK(dbfull()->Put(writeOpt, handles_[1], "k2", big_value));
+    ASSERT_TRUE(dbfull()->GetIntProperty(
+        handles_[1], "rocksdb.num-entries-imm-mem-tables", &int_num));
+    ASSERT_EQ(int_num, 4U);
+    ASSERT_TRUE(dbfull()->GetIntProperty(
+        handles_[1], "rocksdb.num-deletes-imm-mem-tables", &int_num));
+    ASSERT_EQ(int_num, 2U);
+
+    ASSERT_TRUE(dbfull()->GetIntProperty(
+        handles_[1], "rocksdb.estimate-num-keys", &int_num));
+    ASSERT_EQ(int_num, base_total_size + 1);
+
     SetPerfLevel(kDisable);
     ASSERT_TRUE(GetPerfLevel() == kDisable);
   } while (ChangeCompactOptions());
@@ -3198,7 +3227,7 @@ TEST_F(DBTest, GetProperty) {
   ASSERT_TRUE(dbfull()->GetProperty("rocksdb.compaction-pending", &num));
   ASSERT_EQ(num, "0");
   ASSERT_TRUE(dbfull()->GetProperty("rocksdb.estimate-num-keys", &num));
-  ASSERT_EQ(num, "4");
+  ASSERT_EQ(num, "2");
   // Verify the same set of properties through GetIntProperty
   ASSERT_TRUE(
       dbfull()->GetIntProperty("rocksdb.num-immutable-mem-table", &int_num));
@@ -3209,7 +3238,7 @@ TEST_F(DBTest, GetProperty) {
   ASSERT_TRUE(dbfull()->GetIntProperty("rocksdb.compaction-pending", &int_num));
   ASSERT_EQ(int_num, 0U);
   ASSERT_TRUE(dbfull()->GetIntProperty("rocksdb.estimate-num-keys", &int_num));
-  ASSERT_EQ(int_num, 4U);
+  ASSERT_EQ(int_num, 2U);
 
   ASSERT_TRUE(
       dbfull()->GetIntProperty("rocksdb.estimate-table-readers-mem", &int_num));

db/internal_stats.cc

@@ -126,6 +126,10 @@ DBPropertyType GetPropertyType(const Slice& property, bool* is_int_property,
     return kNumEntriesInMutableMemtable;
   } else if (in == "num-entries-imm-mem-tables") {
     return kNumEntriesInImmutableMemtable;
+  } else if (in == "num-deletes-active-mem-table") {
+    return kNumDeletesInMutableMemtable;
+  } else if (in == "num-deletes-imm-mem-tables") {
+    return kNumDeletesInImmutableMemtable;
   } else if (in == "estimate-num-keys") {
     return kEstimatedNumKeys;
   } else if (in == "estimate-table-readers-mem") {
@@ -256,17 +260,28 @@ bool InternalStats::GetIntProperty(DBPropertyType property_type,
       return true;
     case kNumEntriesInMutableMemtable:
       // Current number of entires in the active memtable
-      *value = cfd_->mem()->GetNumEntries();
+      *value = cfd_->mem()->num_entries();
       return true;
     case kNumEntriesInImmutableMemtable:
       // Current number of entries in the immutable memtables
       *value = cfd_->imm()->current()->GetTotalNumEntries();
       return true;
+    case kNumDeletesInMutableMemtable:
+      // Current number of entires in the active memtable
+      *value = cfd_->mem()->num_deletes();
+      return true;
+    case kNumDeletesInImmutableMemtable:
+      // Current number of entries in the immutable memtables
+      *value = cfd_->imm()->current()->GetTotalNumDeletes();
+      return true;
     case kEstimatedNumKeys:
       // Estimate number of entries in the column family:
       // Use estimated entries in tables + total entries in memtables.
-      *value = cfd_->mem()->GetNumEntries() +
-               cfd_->imm()->current()->GetTotalNumEntries() +
+      *value = cfd_->mem()->num_entries() +
+               cfd_->imm()->current()->GetTotalNumEntries() -
+               (cfd_->mem()->num_deletes() +
+                cfd_->imm()->current()->GetTotalNumDeletes()) *
+                   2 +
                vstorage->GetEstimatedActiveKeys();
       return true;
     case kNumSnapshots:

db/internal_stats.h

@@ -40,10 +40,14 @@ enum DBPropertyType : uint32_t {
   kCurSizeActiveMemTable,  // Return current size of the active memtable
   kCurSizeAllMemTables,    // Return current size of all (active + immutable)
                            // memtables
-  kNumEntriesInMutableMemtable,    // Return number of entries in the mutable
+  kNumEntriesInMutableMemtable,    // Return number of deletes in the mutable
                                    // memtable.
   kNumEntriesInImmutableMemtable,  // Return sum of number of entries in all
                                    // the immutable mem tables.
+  kNumDeletesInMutableMemtable,    // Return number of entries in the mutable
+                                   // memtable.
+  kNumDeletesInImmutableMemtable,  // Return sum of number of deletes in all
+                                   // the immutable mem tables.
   kEstimatedNumKeys,  // Estimated total number of keys in the database.
   kEstimatedUsageByTableReaders,  // Estimated memory by table readers.
   kIsFileDeletionEnabled,         // Equals disable_delete_obsolete_files_,

db/memtable.cc

@@ -65,13 +65,15 @@ MemTable::MemTable(const InternalKeyComparator& cmp,
           comparator_, &allocator_, ioptions.prefix_extractor,
           ioptions.info_log)),
       num_entries_(0),
+      num_deletes_(0),
       flush_in_progress_(false),
       flush_completed_(false),
       file_number_(0),
       first_seqno_(0),
       mem_next_logfile_number_(0),
-      locks_(moptions_.inplace_update_support ?
-             moptions_.inplace_update_num_locks : 0),
+      locks_(moptions_.inplace_update_support
+                 ? moptions_.inplace_update_num_locks
+                 : 0),
       prefix_extractor_(ioptions.prefix_extractor),
       should_flush_(ShouldFlushNow()),
       flush_scheduled_(false) {
@@ -313,6 +315,9 @@ void MemTable::Add(SequenceNumber s, ValueType type,
   assert((unsigned)(p + val_size - buf) == (unsigned)encoded_len);
   table_->Insert(handle);
   num_entries_++;
+  if (type == kTypeDeletion) {
+    num_deletes_++;
+  }
 
   if (prefix_bloom_) {
     assert(prefix_extractor_);

db/memtable.h

@@ -164,7 +164,9 @@ class MemTable {
   size_t CountSuccessiveMergeEntries(const LookupKey& key);
 
   // Get total number of entries in the mem table.
-  uint64_t GetNumEntries() const { return num_entries_; }
+  uint64_t num_entries() const { return num_entries_; }
+
+  uint64_t num_deletes() const { return num_deletes_; }
 
   // Returns the edits area that is needed for flushing the memtable
   VersionEdit* GetEdits() { return &edit_; }
@@ -227,6 +229,7 @@ class MemTable {
   unique_ptr<MemTableRep> table_;
 
   uint64_t num_entries_;
+  uint64_t num_deletes_;
 
   // These are used to manage memtable flushes to storage
   bool flush_in_progress_; // started the flush

db/memtable_list.cc

@@ -96,7 +96,15 @@ void MemTableListVersion::AddIterators(
 uint64_t MemTableListVersion::GetTotalNumEntries() const {
   uint64_t total_num = 0;
   for (auto& m : memlist_) {
-    total_num += m->GetNumEntries();
+    total_num += m->num_entries();
+  }
+  return total_num;
+}
+
+uint64_t MemTableListVersion::GetTotalNumDeletes() const {
+  uint64_t total_num = 0;
+  for (auto& m : memlist_) {
+    total_num += m->num_deletes();
   }
   return total_num;
 }

db/memtable_list.h

@@ -57,6 +57,8 @@ class MemTableListVersion {
 
   uint64_t GetTotalNumEntries() const;
 
+  uint64_t GetTotalNumDeletes() const;
+
  private:
   // REQUIRE: m is mutable memtable
   void Add(MemTable* m);

include/rocksdb/db.h

@@ -319,6 +319,8 @@ class DB {
   //  "rocksdb.cur-size-all-mem-tables"
   //  "rocksdb.num-entries-active-mem-table"
   //  "rocksdb.num-entries-imm-mem-tables"
+  //  "rocksdb.num-deletes-active-mem-table"
+  //  "rocksdb.num-deletes-imm-mem-tables"
   //  "rocksdb.estimate-num-keys" - estimated keys in the column family
   //  "rocksdb.estimate-table-readers-mem" - estimated memory used for reding
   //      SST tables, that is not counted as a part of block cache.
@@ -346,6 +348,8 @@ class DB {
   //  "rocksdb.cur-size-all-mem-tables"
   //  "rocksdb.num-entries-active-mem-table"
   //  "rocksdb.num-entries-imm-mem-tables"
+  //  "rocksdb.num-deletes-active-mem-table"
+  //  "rocksdb.num-deletes-imm-mem-tables"
   //  "rocksdb.estimate-num-keys"
   //  "rocksdb.estimate-table-readers-mem"
   //  "rocksdb.is-file-deletions-enabled"