Add DB property estimated number of keys

Summary: Add a DB property of estimated number of live keys, by adding number of entries of all mem tables and all files, subtracted by all deletions in all files.

Test Plan: Add the case in unit tests

Reviewers: hobbymanyp, ljin

Reviewed By: ljin

Subscribers: MarkCallaghan, yoshinorim, leveldb, igor, dhruba

Differential Revision: https://reviews.facebook.net/D20631

HISTORY.md

@@ -10,6 +10,7 @@
 * NewPlainTableFactory instead of bunch of parameters now accepts PlainTableOptions, which is defined in include/rocksdb/table.h
 * Moved include/utilities/*.h to include/rocksdb/utilities/*.h
 * Statistics APIs now take uint32_t as type instead of Tickers. Also make two access functions getTickerCount and histogramData const
+* Add DB property rocksdb.estimate-num-keys, estimated number of live keys in DB.
 
 ## 3.3.0 (7/10/2014)
 ### New Features

db/db_test.cc

@@ -2495,11 +2495,14 @@ TEST(DBTest, GetProperty) {
   ASSERT_EQ(num, "0");
   ASSERT_TRUE(dbfull()->GetProperty("rocksdb.compaction-pending", &num));
   ASSERT_EQ(num, "0");
+  ASSERT_TRUE(dbfull()->GetProperty("rocksdb.estimate-num-keys", &num));
+  ASSERT_EQ(num, "1");
   perf_context.Reset();
 
   ASSERT_OK(dbfull()->Put(writeOpt, "k2", big_value));
   ASSERT_TRUE(dbfull()->GetProperty("rocksdb.num-immutable-mem-table", &num));
   ASSERT_EQ(num, "1");
+  ASSERT_OK(dbfull()->Delete(writeOpt, "k-non-existing"));
   ASSERT_OK(dbfull()->Put(writeOpt, "k3", big_value));
   ASSERT_TRUE(dbfull()->GetProperty("rocksdb.num-immutable-mem-table", &num));
   ASSERT_EQ(num, "2");
@@ -2507,6 +2510,8 @@ TEST(DBTest, GetProperty) {
   ASSERT_EQ(num, "1");
   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");
 
   sleeping_task_high.WakeUp();
   sleeping_task_high.WaitUntilDone();
@@ -2519,6 +2524,8 @@ TEST(DBTest, GetProperty) {
   ASSERT_EQ(num, "0");
   ASSERT_TRUE(dbfull()->GetProperty("rocksdb.compaction-pending", &num));
   ASSERT_EQ(num, "1");
+  ASSERT_TRUE(dbfull()->GetProperty("rocksdb.estimate-num-keys", &num));
+  ASSERT_EQ(num, "4");
   sleeping_task_low.WakeUp();
   sleeping_task_low.WaitUntilDone();
 }

db/internal_stats.cc

@@ -12,8 +12,6 @@
 #include <vector>
 #include "db/column_family.h"
 
-#include "db/column_family.h"
-
 namespace rocksdb {
 
 namespace {
@@ -120,6 +118,8 @@ DBPropertyType GetPropertyType(const Slice& property) {
     return kNumEntriesInMutableMemtable;
   } else if (in == "num-entries-imm-mem-tables") {
     return kNumEntriesInImmutableMemtable;
+  } else if (in == "estimate-num-keys") {
+    return kEstimatedNumKeys;
   }
   return kUnknown;
 }
@@ -207,6 +207,13 @@ bool InternalStats::GetProperty(DBPropertyType property_type,
       // Current size of the active memtable
       *value = std::to_string(cfd_->imm()->current()->GetTotalNumEntries());
       return true;
+    case kEstimatedNumKeys:
+      // Estimate number of entries in the column family:
+      // Use estimated entries in tables + total entries in memtables.
+      *value = std::to_string(cfd_->mem()->GetNumEntries() +
+                              cfd_->imm()->current()->GetTotalNumEntries() +
+                              current->GetEstimatedActiveKeys());
+      return true;
     default:
       return false;
   }

db/internal_stats.h

@@ -38,6 +38,7 @@ enum DBPropertyType {
                                    // memtable.
   kNumEntriesInImmutableMemtable,  // Return sum of number of entries in all
                                    // the immutable mem tables.
+  kEstimatedNumKeys,  // Estimated total number of keys in the database.
   kUnknown,
 };
 

db/version_set.cc

@@ -593,6 +593,14 @@ Status Version::GetPropertiesOfAllTables(TablePropertiesCollection* props) {
   return Status::OK();
 }
 
+uint64_t Version::GetEstimatedActiveKeys() {
+  // Estimation will be not accurate when:
+  // (1) there is merge keys
+  // (2) keys are directly overwritten
+  // (3) deletion on non-existing keys
+  return num_non_deletions_ - num_deletions_;
+}
+
 void Version::AddIterators(const ReadOptions& read_options,
                            const EnvOptions& soptions,
                            std::vector<Iterator*>* iters) {
@@ -749,9 +757,8 @@ Version::Version(ColumnFamilyData* cfd, VersionSet* vset,
     : cfd_(cfd),
       internal_comparator_((cfd == nullptr) ? nullptr
                                             : &cfd->internal_comparator()),
-      user_comparator_((cfd == nullptr)
-                           ? nullptr
-                           : internal_comparator_->user_comparator()),
+      user_comparator_(
+          (cfd == nullptr) ? nullptr : internal_comparator_->user_comparator()),
       table_cache_((cfd == nullptr) ? nullptr : cfd->table_cache()),
       merge_operator_((cfd == nullptr) ? nullptr
                                        : cfd->options()->merge_operator.get()),
@@ -777,12 +784,14 @@ Version::Version(ColumnFamilyData* cfd, VersionSet* vset,
       total_file_size_(0),
       total_raw_key_size_(0),
       total_raw_value_size_(0),
-      num_non_deletions_(0) {
+      num_non_deletions_(0),
+      num_deletions_(0) {
   if (cfd != nullptr && cfd->current() != nullptr) {
       total_file_size_ = cfd->current()->total_file_size_;
       total_raw_key_size_ = cfd->current()->total_raw_key_size_;
       total_raw_value_size_ = cfd->current()->total_raw_value_size_;
       num_non_deletions_ = cfd->current()->num_non_deletions_;
+      num_deletions_ = cfd->current()->num_deletions_;
   }
 }
 
@@ -902,6 +911,7 @@ void Version::UpdateTemporaryStats() {
         total_raw_value_size_ += file_meta->raw_value_size;
         num_non_deletions_ +=
             file_meta->num_entries - file_meta->num_deletions;
+        num_deletions_ += file_meta->num_deletions;
         init_count++;
       }
       total_count++;

db/version_set.h

@@ -232,6 +232,8 @@ class Version {
   // tables' propertis, represented as shared_ptr.
   Status GetPropertiesOfAllTables(TablePropertiesCollection* props);
 
+  uint64_t GetEstimatedActiveKeys();
+
   // used to sort files by size
   struct Fsize {
     int index;
@@ -336,7 +338,8 @@ class Version {
   uint64_t total_raw_value_size_;
   // total number of non-deletion entries
   uint64_t num_non_deletions_;
-
+  // total number of deletion entries
+  uint64_t num_deletions_;
 
   ~Version();