Make rocksdb-deletes faster using bloom filter

Summary:
Wrote a new function in db_impl.c-CheckKeyMayExist that calls Get but with a new parameter turned on which makes Get return false only if bloom filters can guarantee that key is not in database. Delete calls this function and if the option- deletes_use_filter is turned on and CheckKeyMayExist returns false, the delete will be dropped saving:
1. Put of delete type
2. Space in the db,and
3. Compaction time

Test Plan:
make all check;
will run db_stress and db_bench and enhance unit-test once the basic design gets approved

Reviewers: dhruba, haobo, vamsi

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D11607

db/db_bench.cc

@@ -327,6 +327,9 @@ static auto FLAGS_use_adaptive_mutex =
 static auto FLAGS_bytes_per_sync =
   leveldb::Options().bytes_per_sync;
 
+// On true, deletes use bloom-filter and drop the delete if key not present
+static bool FLAGS_deletes_check_filter_first = false;
+
 namespace leveldb {
 
 // Helper for quickly generating random data.
@@ -1111,6 +1114,7 @@ unique_ptr<char []> GenerateKeyFromInt(int v, const char* suffix = "")
     options.max_bytes_for_level_base = FLAGS_max_bytes_for_level_base;
     options.max_bytes_for_level_multiplier =
         FLAGS_max_bytes_for_level_multiplier;
+    options.deletes_check_filter_first = FLAGS_deletes_check_filter_first;
     if (FLAGS_max_bytes_for_level_multiplier_additional.size() > 0) {
       if (FLAGS_max_bytes_for_level_multiplier_additional.size() !=
           (unsigned int)FLAGS_num_levels) {
@@ -2216,6 +2220,9 @@ int main(int argc, char** argv) {
       FLAGS_keys_per_multiget = n;
     }  else if (sscanf(argv[i], "--bytes_per_sync=%ld%c", &l, &junk) == 1) {
       FLAGS_bytes_per_sync = l;
+    } else if (sscanf(argv[i], "--deletes_check_filter_first=%d%c", &n, &junk)
+               == 1 && (n == 0 || n ==1 )) {
+      FLAGS_deletes_check_filter_first = n;
     } else {
       fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
       exit(1);

db/db_impl.cc

@@ -1998,6 +1998,16 @@ int64_t DBImpl::TEST_MaxNextLevelOverlappingBytes() {
 Status DBImpl::Get(const ReadOptions& options,
                    const Slice& key,
                    std::string* value) {
+  return GetImpl(options, key, value);
+}
+
+// If no_IO is true, then returns Status::NotFound if key is not in memtable,
+// immutable-memtable and bloom-filters can guarantee that key is not in db,
+// "value" is garbage string if no_IO is true
+Status DBImpl::GetImpl(const ReadOptions& options,
+                       const Slice& key,
+                       std::string* value,
+                       const bool no_IO) {
   Status s;
 
   StopWatch sw(env_, options_.statistics, DB_GET);
@@ -2026,12 +2036,12 @@ Status DBImpl::Get(const ReadOptions& options,
   // s is both in/out. When in, s could either be OK or MergeInProgress.
   // value will contain the current merge operand in the latter case.
   LookupKey lkey(key, snapshot);
-  if (mem->Get(lkey, value, &s, options_)) {
+  if (mem->Get(lkey, value, &s, options_, no_IO)) {
     // Done
-  } else if (imm.Get(lkey, value, &s, options_)) {
+  } else if (imm.Get(lkey, value, &s, options_, no_IO)) {
     // Done
   } else {
-    current->Get(options, lkey, value, &s, &stats, options_);
+    current->Get(options, lkey, value, &s, &stats, options_, no_IO);
     have_stat_update = true;
   }
   mutex_.Lock();
@@ -2121,6 +2131,12 @@ std::vector<Status> DBImpl::MultiGet(const ReadOptions& options,
   return statList;
 }
 
+bool DBImpl::KeyMayExist(const Slice& key) {
+  std::string value;
+  const Status s = GetImpl(ReadOptions(), key, &value, true);
+  return !s.IsNotFound();
+}
+
 Iterator* DBImpl::NewIterator(const ReadOptions& options) {
   SequenceNumber latest_snapshot;
   Iterator* internal_iter = NewInternalIterator(options, &latest_snapshot);
@@ -2156,6 +2172,10 @@ Status DBImpl::Merge(const WriteOptions& o, const Slice& key,
 }
 
 Status DBImpl::Delete(const WriteOptions& options, const Slice& key) {
+  if (options_.deletes_check_filter_first && !KeyMayExist(key)) {
+    RecordTick(options_.statistics, NUMBER_FILTERED_DELETES);
+    return Status::OK();
+  }
   return DB::Delete(options, key);
 }
 

db/db_impl.h

@@ -48,6 +48,10 @@ class DBImpl : public DB {
   virtual std::vector<Status> MultiGet(const ReadOptions& options,
                                        const std::vector<Slice>& keys,
                                        std::vector<std::string>* values);
+
+  // Returns false if key can't exist- based on memtable, immutable-memtable and
+  // bloom-filters; true otherwise. No IO is performed
+  virtual bool KeyMayExist(const Slice& key);
   virtual Iterator* NewIterator(const ReadOptions&);
   virtual const Snapshot* GetSnapshot();
   virtual void ReleaseSnapshot(const Snapshot* snapshot);
@@ -379,6 +383,12 @@ class DBImpl : public DB {
     SequenceNumber in,
     std::vector<SequenceNumber>& snapshots,
     SequenceNumber* prev_snapshot);
+
+  // Function that Get and KeyMayExist call with no_IO true or false
+  Status GetImpl(const ReadOptions& options,
+                 const Slice& key,
+                 std::string* value,
+                 const bool no_IO = false);
 };
 
 // Sanitize db options.  The caller should delete result.info_log if

db/db_test.cc

@@ -218,6 +218,7 @@ class DBTest {
     kManifestFileSize,
     kCompactOnFlush,
     kPerfOptions,
+    kDeletesFilterFirst,
     kEnd
   };
   int option_config_;
@@ -289,6 +290,9 @@ class DBTest {
         options.rate_limit_delay_milliseconds = 2;
         // TODO -- test more options
         break;
+      case kDeletesFilterFirst:
+        options.deletes_check_filter_first = true;
+        break;
       default:
         break;
     }
@@ -768,6 +772,37 @@ TEST(DBTest, GetEncountersEmptyLevel) {
   } while (ChangeOptions());
 }
 
+// KeyMayExist-API returns false if memtable(s) and in-memory bloom-filters can
+// guarantee that the key doesn't exist in the db, else true. This can lead to
+// a few false positives, but not false negatives. To make test deterministic,
+// use a much larger number of bits per key-20 than bits in the key, so
+// that false positives are eliminated
+TEST(DBTest, KeyMayExist) {
+  do {
+    Options options = CurrentOptions();
+    options.filter_policy = NewBloomFilterPolicy(20);
+    Reopen(&options);
+
+    ASSERT_TRUE(!db_->KeyMayExist("a"));
+
+    ASSERT_OK(db_->Put(WriteOptions(), "a", "b"));
+    ASSERT_TRUE(db_->KeyMayExist("a"));
+
+    dbfull()->Flush(FlushOptions());
+    ASSERT_TRUE(db_->KeyMayExist("a"));
+
+    ASSERT_OK(db_->Delete(WriteOptions(), "a"));
+    ASSERT_TRUE(!db_->KeyMayExist("a"));
+
+    dbfull()->Flush(FlushOptions());
+    dbfull()->CompactRange(nullptr, nullptr);
+    ASSERT_TRUE(!db_->KeyMayExist("a"));
+
+    ASSERT_OK(db_->Delete(WriteOptions(), "c"));
+    ASSERT_TRUE(!db_->KeyMayExist("c"));
+  } while (ChangeOptions());
+}
+
 TEST(DBTest, IterEmpty) {
   Iterator* iter = db_->NewIterator(ReadOptions());
 
@@ -1403,7 +1438,7 @@ class DeleteFilter : public CompactionFilter {
 
 class ChangeFilter : public CompactionFilter {
  public:
-  ChangeFilter(int argv) : argv_(argv) {}
+  explicit ChangeFilter(int argv) : argv_(argv) {}
 
   virtual bool Filter(int level, const Slice& key,
                       const Slice& value, std::string* new_value,
@@ -2970,6 +3005,9 @@ class ModelDB: public DB {
                           Status::NotSupported("Not implemented."));
     return s;
   }
+  virtual bool KeyMayExist(const Slice& key) {
+    return true; // Not Supported directly
+  }
   virtual Iterator* NewIterator(const ReadOptions& options) {
     if (options.snapshot == nullptr) {
       KVMap* saved = new KVMap;

db/memtable.cc

@@ -119,7 +119,7 @@ void MemTable::Add(SequenceNumber s, ValueType type,
 }
 
 bool MemTable::Get(const LookupKey& key, std::string* value, Status* s,
-                  const Options& options) {
+                  const Options& options, const bool check_presence_only) {
   Slice memkey = key.memtable_key();
   Table::Iterator iter(&table_);
   iter.Seek(memkey.data());
@@ -164,6 +164,10 @@ bool MemTable::Get(const LookupKey& key, std::string* value, Status* s,
           return true;
         }
         case kTypeMerge: {
+          if (check_presence_only) {
+            *s = Status::OK();
+            return true;
+          }
           Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
           if (merge_in_progress) {
             merge_operator->Merge(key.user_key(), &v, operand,

db/memtable.h

@@ -63,12 +63,13 @@ class MemTable {
   // If memtable contains a deletion for key, store a NotFound() error
   // in *status and return true.
   // If memtable contains Merge operation as the most recent entry for a key,
-  //   and the merge process does not stop (not reaching a value or delete),
+  //   and if check_presence_only is set, return true with Status::OK,
+  //   else if the merge process does not stop (not reaching a value or delete),
   //   store the current merged result in value and MergeInProgress in s.
   //   return false
   // Else, return false.
   bool Get(const LookupKey& key, std::string* value, Status* s,
-          const Options& options);
+          const Options& options, const bool check_presence_only = false);
 
   // Returns the edits area that is needed for flushing the memtable
   VersionEdit* GetEdits() { return &edit_; }

db/memtablelist.cc

@@ -194,10 +194,10 @@ size_t MemTableList::ApproximateMemoryUsage() {
 // Search all the memtables starting from the most recent one.
 // Return the most recent value found, if any.
 bool MemTableList::Get(const LookupKey& key, std::string* value, Status* s,
-                      const Options& options ) {
+                      const Options& options, const bool check_presence_only) {
   for (list<MemTable*>::iterator it = memlist_.begin();
        it != memlist_.end(); ++it) {
-    if ((*it)->Get(key, value, s, options)) {
+    if ((*it)->Get(key, value, s, options, check_presence_only)) {
       return true;
     }
   }

db/memtablelist.h

@@ -71,7 +71,7 @@ class MemTableList {
   // Search all the memtables starting from the most recent one.
   // Return the most recent value found, if any.
   bool Get(const LookupKey& key, std::string* value, Status* s,
-           const Options& options);
+           const Options& options, const bool check_presence_only = false);
 
   // Returns the list of underlying memtables.
   void GetMemTables(std::vector<MemTable*>* list);

db/table_cache.cc

@@ -112,14 +112,16 @@ Status TableCache::Get(const ReadOptions& options,
                        const Slice& k,
                        void* arg,
                        bool (*saver)(void*, const Slice&, const Slice&, bool),
-                       bool* tableIO) {
+                       bool* tableIO,
+                       void (*mark_key_may_exist)(void*),
+                       const bool no_IO) {
   Cache::Handle* handle = nullptr;
   Status s = FindTable(storage_options_, file_number, file_size,
                        &handle, tableIO);
   if (s.ok()) {
     Table* t =
       reinterpret_cast<Table*>(cache_->Value(handle));
-    s = t->InternalGet(options, k, arg, saver);
+    s = t->InternalGet(options, k, arg, saver, mark_key_may_exist, no_IO);
     cache_->Release(handle);
   }
   return s;

db/table_cache.h

@@ -48,7 +48,9 @@ class TableCache {
              const Slice& k,
              void* arg,
              bool (*handle_result)(void*, const Slice&, const Slice&, bool),
-             bool* tableIO);
+             bool* tableIO,
+             void (*mark_key_may_exist)(void*) = nullptr,
+             const bool no_IO = false);
 
   // Evict any entry for the specified file number
   void Evict(uint64_t file_number);

db/version_set.cc

@@ -244,6 +244,16 @@ struct Saver {
   bool didIO;    // did we do any disk io?
 };
 }
+
+// Called from TableCache::Get when bloom-filters can't guarantee that key does
+// not exist and Get is not permitted to do IO to read the data-block and be
+// certain.
+// Set the key as Found and let the caller know that key-may-exist
+static void MarkKeyMayExist(void* arg) {
+  Saver* s = reinterpret_cast<Saver*>(arg);
+  s->state = kFound;
+}
+
 static bool SaveValue(void* arg, const Slice& ikey, const Slice& v, bool didIO){
   Saver* s = reinterpret_cast<Saver*>(arg);
   ParsedInternalKey parsed_key;
@@ -328,7 +338,8 @@ void Version::Get(const ReadOptions& options,
                   std::string* value,
                   Status *status,
                   GetStats* stats,
-                  const Options& db_options) {
+                  const Options& db_options,
+                  const bool no_IO) {
   Slice ikey = k.internal_key();
   Slice user_key = k.user_key();
   const Comparator* ucmp = vset_->icmp_.user_comparator();
@@ -337,6 +348,9 @@ void Version::Get(const ReadOptions& options,
   auto logger = db_options.info_log;
 
   assert(status->ok() || status->IsMergeInProgress());
+  if (no_IO) {
+    assert(status->ok());
+  }
   Saver saver;
   saver.state = status->ok()? kNotFound : kMerge;
   saver.ucmp = ucmp;
@@ -404,7 +418,8 @@ void Version::Get(const ReadOptions& options,
       FileMetaData* f = files[i];
       bool tableIO = false;
       *status = vset_->table_cache_->Get(options, f->number, f->file_size,
-                                         ikey, &saver, SaveValue, &tableIO);
+                                         ikey, &saver, SaveValue, &tableIO,
+                                         MarkKeyMayExist, no_IO);
       // TODO: examine the behavior for corrupted key
       if (!status->ok()) {
         return;

db/version_set.h

@@ -74,7 +74,8 @@ class Version {
     int seek_file_level;
   };
   void Get(const ReadOptions&, const LookupKey& key, std::string* val,
-           Status* status, GetStats* stats,  const Options& db_option);
+           Status* status, GetStats* stats,  const Options& db_option,
+           const bool no_IO = false);
 
   // Adds "stats" into the current state.  Returns true if a new
   // compaction may need to be triggered, false otherwise.

include/leveldb/db.h

@@ -120,6 +120,11 @@ class DB {
                                        const std::vector<Slice>& keys,
                                        std::vector<std::string>* values) = 0;
 
+  // If the key definitely does not exist in the database, then this method
+  // returns false. Otherwise return true. This check is potentially
+  // lighter-weight than invoking DB::Get(). No IO is performed
+  virtual bool KeyMayExist(const Slice& key) = 0;
+
   // Return a heap-allocated iterator over the contents of the database.
   // The result of NewIterator() is initially invalid (caller must
   // call one of the Seek methods on the iterator before using it).

include/leveldb/options.h

@@ -465,6 +465,15 @@ struct Options {
   // Default: 0
   uint64_t bytes_per_sync;
 
+  // Use bloom-filter for deletes when this is true.
+  // db->Delete first calls KeyMayExist which checks memtable,immutable-memtable
+  // and bloom-filters to determine if the key does not exist in the database.
+  // If the key definitely does not exist, then the delete is a noop.KeyMayExist
+  // only incurs in-memory look up. This optimization avoids writing the delete
+  // to storage when appropriate.
+  // Default: false
+  bool deletes_check_filter_first;
+
 };
 
 // Options that control read operations

include/leveldb/statistics.h

@@ -58,7 +58,9 @@ enum Tickers {
   NUMBER_MULTIGET_KEYS_READ = 19,
   NUMBER_MULTIGET_BYTES_READ = 20,
 
-  TICKER_ENUM_MAX = 21
+  NUMBER_FILTERED_DELETES = 21,
+
+  TICKER_ENUM_MAX = 22
 };
 
 const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
@@ -82,7 +84,8 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
   { NO_ITERATORS, "rocksdb.num.iterators" },
   { NUMBER_MULTIGET_CALLS, "rocksdb.number.multiget.get" },
   { NUMBER_MULTIGET_KEYS_READ, "rocksdb.number.multiget.keys.read" },
-  { NUMBER_MULTIGET_BYTES_READ, "rocksdb.number.multiget.bytes.read" }
+  { NUMBER_MULTIGET_BYTES_READ, "rocksdb.number.multiget.bytes.read" },
+  { NUMBER_FILTERED_DELETES, "rocksdb.number.deletes.filtered" }
 };
 
 /**

table/table.cc

@@ -322,7 +322,9 @@ Iterator* Table::NewIterator(const ReadOptions& options) const {
 Status Table::InternalGet(const ReadOptions& options, const Slice& k,
                           void* arg,
                           bool (*saver)(void*, const Slice&, const Slice&,
-                                        bool)) {
+                                        bool),
+                          void (*mark_key_may_exist)(void*),
+                          const bool no_IO) {
   Status s;
   Iterator* iiter = rep_->index_block->NewIterator(rep_->options.comparator);
   bool done = false;
@@ -338,6 +340,11 @@ Status Table::InternalGet(const ReadOptions& options, const Slice& k,
       // cross one data block, we should be fine.
       RecordTick(rep_->options.statistics, BLOOM_FILTER_USEFUL);
       break;
+    } else if (no_IO) {
+        // Update Saver.state to Found because we are only looking for whether
+        // bloom-filter can guarantee the key is not there when "no_IO"
+        (*mark_key_may_exist)(arg);
+        done = true;
     } else {
       bool didIO = false;
       Iterator* block_iter = BlockReader(this, options, iiter->value(),

table/table.h

@@ -86,7 +86,9 @@ class Table {
   Status InternalGet(
       const ReadOptions&, const Slice& key,
       void* arg,
-      bool (*handle_result)(void* arg, const Slice& k, const Slice& v, bool));
+      bool (*handle_result)(void* arg, const Slice& k, const Slice& v, bool),
+      void (*mark_key_may_exist)(void*) = nullptr,
+      const bool no_IO = false);
 
 
   void ReadMeta(const Footer& footer);

tools/db_stress.cc

@@ -180,6 +180,9 @@ static uint32_t FLAGS_log2_keys_per_lock = 2; // implies 2^2 keys per lock
 // Percentage of times we want to purge redundant keys in memory before flushing
 static uint32_t FLAGS_purge_redundant_percent = 50;
 
+// On true, deletes use bloom-filter and drop the delete if key not present
+static bool FLAGS_deletes_check_filter_first = false;
+
 // Level0 compaction start trigger
 static int FLAGS_level0_file_num_compaction_trigger = 0;
 
@@ -898,8 +901,10 @@ class StressTest {
     fprintf(stdout, "Num times DB reopens: %d\n", FLAGS_reopen);
     fprintf(stdout, "Batches/snapshots   : %d\n",
             FLAGS_test_batches_snapshots);
-    fprintf(stdout, "Purge redundant %%   : %d\n",
+    fprintf(stdout, "Purge redundant %%  : %d\n",
             FLAGS_purge_redundant_percent);
+    fprintf(stdout, "Deletes use filter  : %d\n",
+            FLAGS_deletes_check_filter_first);
     fprintf(stdout, "Num keys per lock   : %d\n",
             1 << FLAGS_log2_keys_per_lock);
 
@@ -955,6 +960,7 @@ class StressTest {
     options.delete_obsolete_files_period_micros =
       FLAGS_delete_obsolete_files_period_micros;
     options.max_manifest_file_size = 1024;
+    options.deletes_check_filter_first = FLAGS_deletes_check_filter_first;
     static Random purge_percent(1000); // no benefit from non-determinism here
     if (purge_percent.Uniform(100) < FLAGS_purge_redundant_percent - 1) {
       options.purge_redundant_kvs_while_flush = false;
@@ -1154,6 +1160,9 @@ int main(int argc, char** argv) {
     } else if (sscanf(argv[i], "--purge_redundant_percent=%d%c", &n, &junk) == 1
         && (n >= 0 && n <= 100)) {
       FLAGS_purge_redundant_percent = n;
+    } else if (sscanf(argv[i], "--deletes_check_filter_first=%d%c", &n, &junk)
+        == 1 && (n == 0 || n == 1)) {
+      FLAGS_deletes_check_filter_first = n;
     } else {
       fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
       exit(1);

util/options.cc

@@ -74,7 +74,8 @@ Options::Options()
       advise_random_on_open(true),
       access_hint_on_compaction_start(NORMAL),
       use_adaptive_mutex(false),
-      bytes_per_sync(0) {
+      bytes_per_sync(0),
+      deletes_check_filter_first(false) {
 }
 
 static const char* const access_hints[] = {
@@ -208,6 +209,8 @@ Options::Dump(Logger* log) const
         use_adaptive_mutex);
     Log(log,"                          Options.bytes_per_sync: %ld",
         bytes_per_sync);
+    Log(log,"              Options.deletes_check_filter_first: %d",
+        deletes_check_filter_first);
 }   // Options::Dump
 
 //

utilities/ttl/db_ttl.cc

@@ -158,6 +158,10 @@ std::vector<Status> DBWithTTL::MultiGet(const ReadOptions& options,
                                supported with TTL"));
 }
 
+bool DBWithTTL::KeyMayExist(const Slice& key) {
+  return db_->KeyMayExist(key);
+}
+
 Status DBWithTTL::Delete(const WriteOptions& wopts, const Slice& key) {
   return db_->Delete(wopts, key);
 }

utilities/ttl/db_ttl.h

@@ -33,6 +33,8 @@ class DBWithTTL : public DB, CompactionFilter {
                                        const std::vector<Slice>& keys,
                                        std::vector<std::string>* values);
 
+  virtual bool KeyMayExist(const Slice& key);
+
   virtual Status Delete(const WriteOptions& wopts, const Slice& key);
 
   virtual Status Merge(const WriteOptions& options,