CuckooTable: add one option to allow identity function for the first hash function

Summary:
MurmurHash becomes expensive when we do millions Get() a second in one
thread. Add this option to allow the first hash function to use identity
function as hash function. It results in QPS increase from 3.7M/s to
~4.3M/s. I did not observe improvement for end to end RocksDB
performance. This may be caused by other bottlenecks that I will address
in a separate diff.

Test Plan:
```
[ljin@dev1964 rocksdb] ./cuckoo_table_reader_test --enable_perf --file_dir=/dev/shm --write --identity_as_first_hash=0
==== Test CuckooReaderTest.WhenKeyExists
==== Test CuckooReaderTest.WhenKeyExistsWithUint64Comparator
==== Test CuckooReaderTest.CheckIterator
==== Test CuckooReaderTest.CheckIteratorUint64
==== Test CuckooReaderTest.WhenKeyNotFound
==== Test CuckooReaderTest.TestReadPerformance
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.272us (3.7 Mqps) with batch size of 0, # of found keys 125829120
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.138us (7.2 Mqps) with batch size of 10, # of found keys 125829120
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.142us (7.1 Mqps) with batch size of 25, # of found keys 125829120
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.142us (7.0 Mqps) with batch size of 50, # of found keys 125829120
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.144us (6.9 Mqps) with batch size of 100, # of found keys 125829120

With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.201us (5.0 Mqps) with batch size of 0, # of found keys 104857600
With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.121us (8.3 Mqps) with batch size of 10, # of found keys 104857600
With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.123us (8.1 Mqps) with batch size of 25, # of found keys 104857600
With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.121us (8.3 Mqps) with batch size of 50, # of found keys 104857600
With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.112us (8.9 Mqps) with batch size of 100, # of found keys 104857600

With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.251us (4.0 Mqps) with batch size of 0, # of found keys 83886080
With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.107us (9.4 Mqps) with batch size of 10, # of found keys 83886080
With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.099us (10.1 Mqps) with batch size of 25, # of found keys 83886080
With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.100us (10.0 Mqps) with batch size of 50, # of found keys 83886080
With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.116us (8.6 Mqps) with batch size of 100, # of found keys 83886080

With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.189us (5.3 Mqps) with batch size of 0, # of found keys 73400320
With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.095us (10.5 Mqps) with batch size of 10, # of found keys 73400320
With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.096us (10.4 Mqps) with batch size of 25, # of found keys 73400320
With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.098us (10.2 Mqps) with batch size of 50, # of found keys 73400320
With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.105us (9.5 Mqps) with batch size of 100, # of found keys 73400320

[ljin@dev1964 rocksdb] ./cuckoo_table_reader_test --enable_perf --file_dir=/dev/shm --write --identity_as_first_hash=1
==== Test CuckooReaderTest.WhenKeyExists
==== Test CuckooReaderTest.WhenKeyExistsWithUint64Comparator
==== Test CuckooReaderTest.CheckIterator
==== Test CuckooReaderTest.CheckIteratorUint64
==== Test CuckooReaderTest.WhenKeyNotFound
==== Test CuckooReaderTest.TestReadPerformance
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.230us (4.3 Mqps) with batch size of 0, # of found keys 125829120
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.086us (11.7 Mqps) with batch size of 10, # of found keys 125829120
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.088us (11.3 Mqps) with batch size of 25, # of found keys 125829120
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.083us (12.1 Mqps) with batch size of 50, # of found keys 125829120
With 125829120 items, utilization is 93.75%, number of hash functions: 2.
Time taken per op is 0.083us (12.1 Mqps) with batch size of 100, # of found keys 125829120

With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.159us (6.3 Mqps) with batch size of 0, # of found keys 104857600
With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.078us (12.8 Mqps) with batch size of 10, # of found keys 104857600
With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.080us (12.6 Mqps) with batch size of 25, # of found keys 104857600
With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.080us (12.5 Mqps) with batch size of 50, # of found keys 104857600
With 104857600 items, utilization is 78.12%, number of hash functions: 2.
Time taken per op is 0.082us (12.2 Mqps) with batch size of 100, # of found keys 104857600

With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.154us (6.5 Mqps) with batch size of 0, # of found keys 83886080
With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.077us (13.0 Mqps) with batch size of 10, # of found keys 83886080
With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.077us (12.9 Mqps) with batch size of 25, # of found keys 83886080
With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.078us (12.8 Mqps) with batch size of 50, # of found keys 83886080
With 83886080 items, utilization is 62.50%, number of hash functions: 2.
Time taken per op is 0.079us (12.6 Mqps) with batch size of 100, # of found keys 83886080

With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.218us (4.6 Mqps) with batch size of 0, # of found keys 73400320
With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.083us (12.0 Mqps) with batch size of 10, # of found keys 73400320
With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.085us (11.7 Mqps) with batch size of 25, # of found keys 73400320
With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.086us (11.6 Mqps) with batch size of 50, # of found keys 73400320
With 73400320 items, utilization is 54.69%, number of hash functions: 2.
Time taken per op is 0.078us (12.8 Mqps) with batch size of 100, # of found keys 73400320
```

Reviewers: sdong, igor, yhchiang

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D23451

HISTORY.md

@@ -2,11 +2,12 @@
 
 ## Unreleased (will be released with 3.6)
 ### Disk format changes
-* If you're using RocksDB on ARM platforms and you're using default bloom filter, there is a disk format change you need to be aware of. There are three steps you need to do when you convert to new release: 1. turn off filter policy, 2. compact the whole database, 3. turn on filter policy 
+* If you're using RocksDB on ARM platforms and you're using default bloom filter, there is a disk format change you need to be aware of. There are three steps you need to do when you convert to new release: 1. turn off filter policy, 2. compact the whole database, 3. turn on filter policy
 
 ### Behavior changes
 * We have refactored our system of stalling writes.  Any stall-related statistics' meanings are changed. Instead of per-write stall counts, we now count stalls per-epoch, where epochs are periods between flushes and compactions. You'll find more information in our Tuning Perf Guide once we release RocksDB 3.6.
 * When disableDataSync=true, we no longer sync the MANIFEST file.
+* Add identity_as_first_hash property to CuckooTable. SST file needs to be rebuilt to be opened by reader properly.
 
 ----- Past Releases -----
 

db/db_bench.cc

@@ -514,6 +514,9 @@ DEFINE_int64(keys_per_prefix, 0, "control average number of keys generated "
              "i.e. use the prefix comes with the generated random number.");
 DEFINE_bool(enable_io_prio, false, "Lower the background flush/compaction "
             "threads' IO priority");
+DEFINE_bool(identity_as_first_hash, false, "the first hash function of cuckoo "
+            "table becomes an identity function. This is only valid when key "
+            "is 8 bytes");
 
 enum RepFactory {
   kSkipList,
@@ -1739,8 +1742,11 @@ class Benchmark {
         fprintf(stderr, "Invalid cuckoo_hash_ratio\n");
         exit(1);
       }
+      rocksdb::CuckooTableOptions table_options;
+      table_options.hash_table_ratio = FLAGS_cuckoo_hash_ratio;
+      table_options.identity_as_first_hash = FLAGS_identity_as_first_hash;
       options.table_factory = std::shared_ptr<TableFactory>(
-          NewCuckooTableFactory(FLAGS_cuckoo_hash_ratio));
+          NewCuckooTableFactory(table_options));
     } else {
       BlockBasedTableOptions block_based_options;
       if (FLAGS_use_hash_search) {

include/rocksdb/table.h

@@ -251,23 +251,36 @@ struct CuckooTablePropertyNames {
   // Denotes if the key sorted in the file is Internal Key (if false)
   // or User Key only (if true).
   static const std::string kIsLastLevel;
+  // Indicate if using identity function for the first hash function.
+  static const std::string kIdentityAsFirstHash;
+};
+
+struct CuckooTableOptions {
+  // Determines the utilization of hash tables. Smaller values
+  // result in larger hash tables with fewer collisions.
+  double hash_table_ratio = 0.9;
+  // A property used by builder to determine the depth to go to
+  // to search for a path to displace elements in case of
+  // collision. See Builder.MakeSpaceForKey method. Higher
+  // values result in more efficient hash tables with fewer
+  // lookups but take more time to build.
+  uint32_t max_search_depth = 100;
+  // In case of collision while inserting, the builder
+  // attempts to insert in the next cuckoo_block_size
+  // locations before skipping over to the next Cuckoo hash
+  // function. This makes lookups more cache friendly in case
+  // of collisions.
+  uint32_t cuckoo_block_size = 5;
+  // If this options is enabled, user key is treated as uint64_t and its value
+  // is used as hash value directly. This option changes builder's behavior.
+  // Reader ignore this option and behave according to what specified in table
+  // property.
+  bool identity_as_first_hash = false;
 };
 
 // Cuckoo Table Factory for SST table format using Cache Friendly Cuckoo Hashing
-// @hash_table_ratio: Determines the utilization of hash tables. Smaller values
-//                    result in larger hash tables with fewer collisions.
-// @max_search_depth: A property used by builder to determine the depth to go to
-//                    to search for a path to displace elements in case of
-//                    collision. See Builder.MakeSpaceForKey method.  Higher
-//                    values result in more efficient hash tables with fewer
-//                    lookups but take more time to build.
-// @cuckoo_block_size: In case of collision while inserting, the builder
-//                     attempts to insert in the next cuckoo_block_size
-//                     locations before skipping over to the next Cuckoo hash
-//                     function. This makes lookups more cache friendly in case
-//                     of collisions.
-extern TableFactory* NewCuckooTableFactory(double hash_table_ratio = 0.9,
-    uint32_t max_search_depth = 100, uint32_t cuckoo_block_size = 5);
+extern TableFactory* NewCuckooTableFactory(
+    const CuckooTableOptions& table_options = CuckooTableOptions());
 
 #endif  // ROCKSDB_LITE
 

table/cuckoo_table_builder.cc

@@ -35,6 +35,8 @@ const std::string CuckooTablePropertyNames::kIsLastLevel =
       "rocksdb.cuckoo.file.islastlevel";
 const std::string CuckooTablePropertyNames::kCuckooBlockSize =
       "rocksdb.cuckoo.hash.cuckooblocksize";
+const std::string CuckooTablePropertyNames::kIdentityAsFirstHash =
+      "rocksdb.cuckoo.hash.identityfirst";
 
 // Obtained by running echo rocksdb.table.cuckoo | sha1sum
 extern const uint64_t kCuckooTableMagicNumber = 0x926789d0c5f17873ull;
@@ -43,6 +45,7 @@ CuckooTableBuilder::CuckooTableBuilder(
     WritableFile* file, double max_hash_table_ratio,
     uint32_t max_num_hash_table, uint32_t max_search_depth,
     const Comparator* user_comparator, uint32_t cuckoo_block_size,
+    bool identity_as_first_hash,
     uint64_t (*get_slice_hash)(const Slice&, uint32_t, uint64_t))
     : num_hash_func_(2),
       file_(file),
@@ -54,6 +57,7 @@ CuckooTableBuilder::CuckooTableBuilder(
       is_last_level_file_(false),
       has_seen_first_key_(false),
       ucomp_(user_comparator),
+      identity_as_first_hash_(identity_as_first_hash),
       get_slice_hash_(get_slice_hash),
       closed_(false) {
   // Data is in a huge block.
@@ -119,7 +123,7 @@ Status CuckooTableBuilder::MakeHashTable(std::vector<CuckooBucket>* buckets) {
     for (uint32_t hash_cnt = 0; hash_cnt < num_hash_func_ && !bucket_found;
         ++hash_cnt) {
       uint64_t hash_val = CuckooHash(user_key, hash_cnt,
-          hash_table_size_minus_one, get_slice_hash_);
+          hash_table_size_minus_one, identity_as_first_hash_, get_slice_hash_);
       // If there is a collision, check next cuckoo_block_size_ locations for
       // empty locations. While checking, if we reach end of the hash table,
       // stop searching and proceed for next hash function.
@@ -149,7 +153,7 @@ Status CuckooTableBuilder::MakeHashTable(std::vector<CuckooBucket>* buckets) {
       // We don't really need to rehash the entire table because old hashes are
       // still valid and we only increased the number of hash functions.
       uint64_t hash_val = CuckooHash(user_key, num_hash_func_,
-          hash_table_size_minus_one, get_slice_hash_);
+          hash_table_size_minus_one, identity_as_first_hash_, get_slice_hash_);
       ++num_hash_func_;
       for (uint32_t block_idx = 0; block_idx < cuckoo_block_size_;
           ++block_idx, ++hash_val) {
@@ -261,6 +265,10 @@ Status CuckooTableBuilder::Finish() {
     CuckooTablePropertyNames::kCuckooBlockSize].assign(
         reinterpret_cast<const char*>(&cuckoo_block_size_),
         sizeof(cuckoo_block_size_));
+  properties_.user_collected_properties[
+    CuckooTablePropertyNames::kIdentityAsFirstHash].assign(
+        reinterpret_cast<const char*>(&identity_as_first_hash_),
+        sizeof(identity_as_first_hash_));
 
   // Write meta blocks.
   MetaIndexBuilder meta_index_builder;
@@ -380,7 +388,8 @@ bool CuckooTableBuilder::MakeSpaceForKey(
       uint64_t child_bucket_id = CuckooHash(
           (is_last_level_file_ ? kvs_[curr_bucket.vector_idx].first :
            ExtractUserKey(Slice(kvs_[curr_bucket.vector_idx].first))),
-          hash_cnt, hash_table_size_minus_one, get_slice_hash_);
+          hash_cnt, hash_table_size_minus_one, identity_as_first_hash_,
+          get_slice_hash_);
       // Iterate inside Cuckoo Block.
       for (uint32_t block_idx = 0; block_idx < cuckoo_block_size_;
           ++block_idx, ++child_bucket_id) {

table/cuckoo_table_builder.h

@@ -24,6 +24,7 @@ class CuckooTableBuilder: public TableBuilder {
       WritableFile* file, double max_hash_table_ratio,
       uint32_t max_num_hash_func, uint32_t max_search_depth,
       const Comparator* user_comparator, uint32_t cuckoo_block_size,
+      bool identity_as_first_hash,
       uint64_t (*get_slice_hash)(const Slice&, uint32_t, uint64_t));
 
   // REQUIRES: Either Finish() or Abandon() has been called.
@@ -87,6 +88,7 @@ class CuckooTableBuilder: public TableBuilder {
   TableProperties properties_;
   bool has_seen_first_key_;
   const Comparator* ucomp_;
+  bool identity_as_first_hash_;
   uint64_t (*get_slice_hash_)(const Slice& s, uint32_t index,
     uint64_t max_num_buckets);
   std::string largest_user_key_ = "";

table/cuckoo_table_builder_test.cc

@@ -133,7 +133,7 @@ TEST(CuckooBuilderTest, SuccessWithEmptyFile) {
   fname = test::TmpDir() + "/EmptyFile";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      4, 100, BytewiseComparator(), 1, GetSliceHash);
+      4, 100, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
   ASSERT_EQ(0UL, builder.FileSize());
   ASSERT_OK(builder.Finish());
@@ -162,7 +162,7 @@ TEST(CuckooBuilderTest, WriteSuccessNoCollisionFullKey) {
   fname = test::TmpDir() + "/NoCollisionFullKey";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 100, BytewiseComparator(), 1, GetSliceHash);
+      num_hash_fun, 100, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(keys[i]), Slice(values[i]));
@@ -202,7 +202,7 @@ TEST(CuckooBuilderTest, WriteSuccessWithCollisionFullKey) {
   fname = test::TmpDir() + "/WithCollisionFullKey";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 100, BytewiseComparator(), 1, GetSliceHash);
+      num_hash_fun, 100, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(keys[i]), Slice(values[i]));
@@ -243,7 +243,8 @@ TEST(CuckooBuilderTest, WriteSuccessWithCollisionAndCuckooBlock) {
   fname = test::TmpDir() + "/WithCollisionFullKey2";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 100, BytewiseComparator(), cuckoo_block_size, GetSliceHash);
+      num_hash_fun, 100, BytewiseComparator(), cuckoo_block_size, false,
+      GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(keys[i]), Slice(values[i]));
@@ -288,7 +289,7 @@ TEST(CuckooBuilderTest, WithCollisionPathFullKey) {
   fname = test::TmpDir() + "/WithCollisionPathFullKey";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 100, BytewiseComparator(), 1, GetSliceHash);
+      num_hash_fun, 100, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(keys[i]), Slice(values[i]));
@@ -330,7 +331,7 @@ TEST(CuckooBuilderTest, WithCollisionPathFullKeyAndCuckooBlock) {
   fname = test::TmpDir() + "/WithCollisionPathFullKeyAndCuckooBlock";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 100, BytewiseComparator(), 2, GetSliceHash);
+      num_hash_fun, 100, BytewiseComparator(), 2, false, GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(keys[i]), Slice(values[i]));
@@ -366,7 +367,7 @@ TEST(CuckooBuilderTest, WriteSuccessNoCollisionUserKey) {
   fname = test::TmpDir() + "/NoCollisionUserKey";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 100, BytewiseComparator(), 1, GetSliceHash);
+      num_hash_fun, 100, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(GetInternalKey(user_keys[i], true)), Slice(values[i]));
@@ -402,7 +403,7 @@ TEST(CuckooBuilderTest, WriteSuccessWithCollisionUserKey) {
   fname = test::TmpDir() + "/WithCollisionUserKey";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 100, BytewiseComparator(), 1, GetSliceHash);
+      num_hash_fun, 100, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(GetInternalKey(user_keys[i], true)), Slice(values[i]));
@@ -440,7 +441,7 @@ TEST(CuckooBuilderTest, WithCollisionPathUserKey) {
   fname = test::TmpDir() + "/WithCollisionPathUserKey";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 2, BytewiseComparator(), 1, GetSliceHash);
+      num_hash_fun, 2, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(GetInternalKey(user_keys[i], true)), Slice(values[i]));
@@ -478,7 +479,7 @@ TEST(CuckooBuilderTest, FailWhenCollisionPathTooLong) {
   fname = test::TmpDir() + "/WithCollisionPathUserKey";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 2, BytewiseComparator(), 1, GetSliceHash);
+      num_hash_fun, 2, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
   for (uint32_t i = 0; i < user_keys.size(); i++) {
     builder.Add(Slice(GetInternalKey(user_keys[i], false)), Slice("value"));
@@ -498,7 +499,7 @@ TEST(CuckooBuilderTest, FailWhenSameKeyInserted) {
   fname = test::TmpDir() + "/FailWhenSameKeyInserted";
   ASSERT_OK(env_->NewWritableFile(fname, &writable_file, env_options_));
   CuckooTableBuilder builder(writable_file.get(), kHashTableRatio,
-      num_hash_fun, 100, BytewiseComparator(), 1, GetSliceHash);
+      num_hash_fun, 100, BytewiseComparator(), 1, false, GetSliceHash);
   ASSERT_OK(builder.status());
 
   builder.Add(Slice(GetInternalKey(user_key, false)), Slice("value1"));

table/cuckoo_table_factory.cc

@@ -30,9 +30,10 @@ TableBuilder* CuckooTableFactory::NewTableBuilder(
     const InternalKeyComparator& internal_comparator,
     WritableFile* file, const CompressionType,
     const CompressionOptions&) const {
-  return new CuckooTableBuilder(file, hash_table_ratio_, 64,
-      max_search_depth_, internal_comparator.user_comparator(),
-      cuckoo_block_size_, nullptr);
+  return new CuckooTableBuilder(file, table_options_.hash_table_ratio, 64,
+      table_options_.max_search_depth, internal_comparator.user_comparator(),
+      table_options_.cuckoo_block_size, table_options_.identity_as_first_hash,
+      nullptr);
 }
 
 std::string CuckooTableFactory::GetPrintableTableOptions() const {
@@ -42,21 +43,22 @@ std::string CuckooTableFactory::GetPrintableTableOptions() const {
   char buffer[kBufferSize];
 
   snprintf(buffer, kBufferSize, "  hash_table_ratio: %lf\n",
-           hash_table_ratio_);
+           table_options_.hash_table_ratio);
   ret.append(buffer);
   snprintf(buffer, kBufferSize, "  max_search_depth: %u\n",
-           max_search_depth_);
+           table_options_.max_search_depth);
   ret.append(buffer);
   snprintf(buffer, kBufferSize, "  cuckoo_block_size: %u\n",
-           cuckoo_block_size_);
+           table_options_.cuckoo_block_size);
+  ret.append(buffer);
+  snprintf(buffer, kBufferSize, "  identity_as_first_hash: %d\n",
+           table_options_.identity_as_first_hash);
   ret.append(buffer);
   return ret;
 }
 
-TableFactory* NewCuckooTableFactory(double hash_table_ratio,
-    uint32_t max_search_depth, uint32_t cuckoo_block_size) {
-  return new CuckooTableFactory(
-      hash_table_ratio, max_search_depth, cuckoo_block_size);
+TableFactory* NewCuckooTableFactory(const CuckooTableOptions& table_options) {
+  return new CuckooTableFactory(table_options);
 }
 
 }  // namespace rocksdb

table/cuckoo_table_factory.h

@@ -16,6 +16,7 @@ namespace rocksdb {
 const uint32_t kCuckooMurmurSeedMultiplier = 816922183;
 static inline uint64_t CuckooHash(
     const Slice& user_key, uint32_t hash_cnt, uint64_t table_size_minus_one,
+    bool identity_as_first_hash,
     uint64_t (*get_slice_hash)(const Slice&, uint32_t, uint64_t)) {
 #ifndef NDEBUG
   // This part is used only in unit tests.
@@ -23,6 +24,10 @@ static inline uint64_t CuckooHash(
     return get_slice_hash(user_key, hash_cnt, table_size_minus_one + 1);
   }
 #endif
+  if (hash_cnt == 0 && identity_as_first_hash) {
+    return (*reinterpret_cast<const int64_t*>(user_key.data())) &
+           table_size_minus_one;
+  }
   return MurmurHash(user_key.data(), user_key.size(),
       kCuckooMurmurSeedMultiplier * hash_cnt) & table_size_minus_one;
 }
@@ -36,11 +41,8 @@ static inline uint64_t CuckooHash(
 // - Does not support Merge operations.
 class CuckooTableFactory : public TableFactory {
  public:
-  CuckooTableFactory(double hash_table_ratio, uint32_t max_search_depth,
-      uint32_t cuckoo_block_size)
-    : hash_table_ratio_(hash_table_ratio),
-      max_search_depth_(max_search_depth),
-      cuckoo_block_size_(cuckoo_block_size) {}
+  explicit CuckooTableFactory(const CuckooTableOptions& table_options)
+    : table_options_(table_options) {}
   ~CuckooTableFactory() {}
 
   const char* Name() const override { return "CuckooTable"; }
@@ -63,9 +65,7 @@ class CuckooTableFactory : public TableFactory {
   std::string GetPrintableTableOptions() const override;
 
  private:
-  const double hash_table_ratio_;
-  const uint32_t max_search_depth_;
-  const uint32_t cuckoo_block_size_;
+  const CuckooTableOptions table_options_;
 };
 
 }  // namespace rocksdb

table/cuckoo_table_reader.cc

@@ -50,13 +50,13 @@ CuckooTableReader::CuckooTableReader(
   auto& user_props = props->user_collected_properties;
   auto hash_funs = user_props.find(CuckooTablePropertyNames::kNumHashFunc);
   if (hash_funs == user_props.end()) {
-    status_ = Status::InvalidArgument("Number of hash functions not found");
+    status_ = Status::Corruption("Number of hash functions not found");
     return;
   }
   num_hash_func_ = *reinterpret_cast<const uint32_t*>(hash_funs->second.data());
   auto unused_key = user_props.find(CuckooTablePropertyNames::kEmptyKey);
   if (unused_key == user_props.end()) {
-    status_ = Status::InvalidArgument("Empty bucket value not found");
+    status_ = Status::Corruption("Empty bucket value not found");
     return;
   }
   unused_key_ = unused_key->second;
@@ -64,7 +64,7 @@ CuckooTableReader::CuckooTableReader(
   key_length_ = props->fixed_key_len;
   auto value_length = user_props.find(CuckooTablePropertyNames::kValueLength);
   if (value_length == user_props.end()) {
-    status_ = Status::InvalidArgument("Value length not found");
+    status_ = Status::Corruption("Value length not found");
     return;
   }
   value_length_ = *reinterpret_cast<const uint32_t*>(
@@ -74,21 +74,31 @@ CuckooTableReader::CuckooTableReader(
   auto hash_table_size = user_props.find(
       CuckooTablePropertyNames::kHashTableSize);
   if (hash_table_size == user_props.end()) {
-    status_ = Status::InvalidArgument("Hash table size not found");
+    status_ = Status::Corruption("Hash table size not found");
     return;
   }
   table_size_minus_one_ = *reinterpret_cast<const uint64_t*>(
       hash_table_size->second.data()) - 1;
   auto is_last_level = user_props.find(CuckooTablePropertyNames::kIsLastLevel);
   if (is_last_level == user_props.end()) {
-    status_ = Status::InvalidArgument("Is last level not found");
+    status_ = Status::Corruption("Is last level not found");
     return;
   }
   is_last_level_ = *reinterpret_cast<const bool*>(is_last_level->second.data());
+
+  auto identity_as_first_hash = user_props.find(
+      CuckooTablePropertyNames::kIdentityAsFirstHash);
+  if (identity_as_first_hash == user_props.end()) {
+    status_ = Status::Corruption("identity as first hash not found");
+    return;
+  }
+  identity_as_first_hash_ = *reinterpret_cast<const bool*>(
+      identity_as_first_hash->second.data());
+
   auto cuckoo_block_size = user_props.find(
       CuckooTablePropertyNames::kCuckooBlockSize);
   if (cuckoo_block_size == user_props.end()) {
-    status_ = Status::InvalidArgument("Cuckoo block size not found");
+    status_ = Status::Corruption("Cuckoo block size not found");
     return;
   }
   cuckoo_block_size_ = *reinterpret_cast<const uint32_t*>(
@@ -106,7 +116,8 @@ Status CuckooTableReader::Get(
   Slice user_key = ExtractUserKey(key);
   for (uint32_t hash_cnt = 0; hash_cnt < num_hash_func_; ++hash_cnt) {
     uint64_t offset = bucket_length_ * CuckooHash(
-        user_key, hash_cnt, table_size_minus_one_, get_slice_hash_);
+        user_key, hash_cnt, table_size_minus_one_, identity_as_first_hash_,
+        get_slice_hash_);
     const char* bucket = &file_data_.data()[offset];
     for (uint32_t block_idx = 0; block_idx < cuckoo_block_size_;
         ++block_idx, bucket += bucket_length_) {
@@ -117,7 +128,7 @@ Status CuckooTableReader::Get(
       // Here, we compare only the user key part as we support only one entry
       // per user key and we don't support sanpshot.
       if (ucomp_->Compare(user_key, Slice(bucket, user_key.size())) == 0) {
-        Slice value = Slice(&bucket[key_length_], value_length_);
+        Slice value(bucket + key_length_, value_length_);
         if (is_last_level_) {
           ParsedInternalKey found_ikey(
               Slice(bucket, key_length_), 0, kTypeValue);
@@ -140,7 +151,8 @@ void CuckooTableReader::Prepare(const Slice& key) {
   // Prefetch the first Cuckoo Block.
   Slice user_key = ExtractUserKey(key);
   uint64_t addr = reinterpret_cast<uint64_t>(file_data_.data()) +
-    bucket_length_ * CuckooHash(user_key, 0, table_size_minus_one_, nullptr);
+    bucket_length_ * CuckooHash(user_key, 0, table_size_minus_one_,
+                                identity_as_first_hash_, nullptr);
   uint64_t end_addr = addr + cuckoo_block_bytes_minus_one_;
   for (addr &= CACHE_LINE_MASK; addr < end_addr; addr += CACHE_LINE_SIZE) {
     PREFETCH(reinterpret_cast<const char*>(addr), 0, 3);

table/cuckoo_table_reader.h

@@ -64,6 +64,7 @@ class CuckooTableReader: public TableReader {
   std::unique_ptr<RandomAccessFile> file_;
   Slice file_data_;
   bool is_last_level_;
+  bool identity_as_first_hash_;
   std::shared_ptr<const TableProperties> table_props_;
   Status status_;
   uint32_t num_hash_func_;

table/cuckoo_table_reader_test.cc

@@ -38,6 +38,7 @@ DEFINE_string(file_dir, "", "Directory where the files will be created"
 DEFINE_bool(enable_perf, false, "Run Benchmark Tests too.");
 DEFINE_bool(write, false,
     "Should write new values to file in performance tests?");
+DEFINE_bool(identity_as_first_hash, true, "use identity as first hash");
 
 namespace rocksdb {
 
@@ -109,7 +110,8 @@ class CuckooReaderTest {
     std::unique_ptr<WritableFile> writable_file;
     ASSERT_OK(env->NewWritableFile(fname, &writable_file, env_options));
     CuckooTableBuilder builder(
-        writable_file.get(), 0.9, kNumHashFunc, 100, ucomp, 2, GetSliceHash);
+        writable_file.get(), 0.9, kNumHashFunc, 100, ucomp, 2, false,
+        GetSliceHash);
     ASSERT_OK(builder.status());
     for (uint32_t key_idx = 0; key_idx < num_items; ++key_idx) {
       builder.Add(Slice(keys[key_idx]), Slice(values[key_idx]));
@@ -375,8 +377,15 @@ TEST(CuckooReaderTest, WhenKeyNotFound) {
 
 // Performance tests
 namespace {
+int64_t found_count = 0;
+std::string value;
 bool DoNothing(void* arg, const ParsedInternalKey& k, const Slice& v) {
   // Deliberately empty.
+  if (*reinterpret_cast<const int32_t*>(k.user_key.data()) ==
+      *reinterpret_cast<const int32_t*>(v.data())) {
+    ++found_count;
+    value.assign(v.data(), v.size());
+  }
   return false;
 }
 
@@ -389,12 +398,14 @@ bool CheckValue(void* cnt_ptr, const ParsedInternalKey& k, const Slice& v) {
 }
 
 void GetKeys(uint64_t num, std::vector<std::string>* keys) {
+  keys->clear();
   IterKey k;
   k.SetInternalKey("", 0, kTypeValue);
   std::string internal_key_suffix = k.GetKey().ToString();
   ASSERT_EQ(static_cast<size_t>(8), internal_key_suffix.size());
   for (uint64_t key_idx = 0; key_idx < num; ++key_idx) {
-    std::string new_key(reinterpret_cast<char*>(&key_idx), sizeof(key_idx));
+    uint64_t value = 2 * key_idx;
+    std::string new_key(reinterpret_cast<char*>(&value), sizeof(value));
     new_key += internal_key_suffix;
     keys->push_back(new_key);
   }
@@ -422,7 +433,8 @@ void WriteFile(const std::vector<std::string>& keys,
   ASSERT_OK(env->NewWritableFile(fname, &writable_file, env_options));
   CuckooTableBuilder builder(
       writable_file.get(), hash_ratio,
-      64, 1000, test::Uint64Comparator(), 5, nullptr);
+      64, 1000, test::Uint64Comparator(), 5,
+      FLAGS_identity_as_first_hash, nullptr);
   ASSERT_OK(builder.status());
   for (uint64_t key_idx = 0; key_idx < num; ++key_idx) {
     // Value is just a part of key.
@@ -482,27 +494,36 @@ void ReadKeys(uint64_t num, uint32_t batch_size) {
       " hash functions: %u.\n", num, num * 100.0 / (table_size), num_hash_fun);
   ReadOptions r_options;
 
+  std::vector<uint64_t> keys;
+  keys.reserve(num);
+  for (uint64_t i = 0; i < num; ++i) {
+    keys.push_back(2 * i);
+  }
+  std::random_shuffle(keys.begin(), keys.end());
+
+  found_count = 0;
   uint64_t start_time = env->NowMicros();
   if (batch_size > 0) {
     for (uint64_t i = 0; i < num; i += batch_size) {
       for (uint64_t j = i; j < i+batch_size && j < num; ++j) {
-        reader.Prepare(Slice(reinterpret_cast<char*>(&j), 16));
+        reader.Prepare(Slice(reinterpret_cast<char*>(&keys[j]), 16));
       }
       for (uint64_t j = i; j < i+batch_size && j < num; ++j) {
-        reader.Get(r_options, Slice(reinterpret_cast<char*>(&j), 16),
-            nullptr, DoNothing, nullptr);
+        reader.Get(r_options, Slice(reinterpret_cast<char*>(&keys[j]), 16),
+                   nullptr, DoNothing, nullptr);
       }
     }
   } else {
     for (uint64_t i = 0; i < num; i++) {
-      reader.Get(r_options, Slice(reinterpret_cast<char*>(&i), 16), nullptr,
-          DoNothing, nullptr);
+      reader.Get(r_options, Slice(reinterpret_cast<char*>(&keys[i]), 16),
+                 nullptr, DoNothing, nullptr);
     }
   }
   float time_per_op = (env->NowMicros() - start_time) * 1.0 / num;
   fprintf(stderr,
-      "Time taken per op is %.3fus (%.1f Mqps) with batch size of %u\n",
-      time_per_op, 1.0 / time_per_op, batch_size);
+      "Time taken per op is %.3fus (%.1f Mqps) with batch size of %u, "
+      "# of found keys %ld\n",
+      time_per_op, 1.0 / time_per_op, batch_size, found_count);
 }
 }  // namespace.
 
@@ -514,16 +535,16 @@ TEST(CuckooReaderTest, TestReadPerformance) {
   // These numbers are chosen to have a hash utilizaiton % close to
   // 0.9, 0.75, 0.6 and 0.5 respectively.
   // They all create 128 M buckets.
-  std::vector<uint64_t> nums = {120*1000*1000, 100*1000*1000, 80*1000*1000,
-    70*1000*1000};
+  std::vector<uint64_t> nums = {120*1024*1024, 100*1024*1024, 80*1024*1024,
+    70*1024*1024};
 #ifndef NDEBUG
   fprintf(stdout,
       "WARNING: Not compiled with DNDEBUG. Performance tests may be slow.\n");
 #endif
   std::vector<std::string> keys;
-  GetKeys(*std::max_element(nums.begin(), nums.end()), &keys);
   for (uint64_t num : nums) {
     if (FLAGS_write || !Env::Default()->FileExists(GetFileName(num))) {
+      GetKeys(num, &keys);
       WriteFile(keys, num, hash_ratio);
     }
     ReadKeys(num, 0);

table/table_reader_bench.cc

@@ -260,8 +260,9 @@ int main(int argc, char** argv) {
   if (FLAGS_table_factory == "cuckoo_hash") {
     options.allow_mmap_reads = true;
     env_options.use_mmap_reads = true;
-
-    tf.reset(rocksdb::NewCuckooTableFactory(0.75));
+    rocksdb::CuckooTableOptions table_options;
+    table_options.hash_table_ratio = 0.75;
+    tf.reset(rocksdb::NewCuckooTableFactory(table_options));
   } else if (FLAGS_table_factory == "plain_table") {
     options.allow_mmap_reads = true;
     env_options.use_mmap_reads = true;