diff --git a/db/db_impl.h b/db/db_impl.h
index bc251492b7..011066bf44 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -673,10 +673,14 @@ class DBImpl : public DB {
   // batch which will be written to memtable later during the commit, and in
   // WritePrepared it is guaranteed since it will be used only for WAL markers
   // which will never be written to memtable.
+  // batch_cnt is expected to be non-zero in seq_per_batch mode and indicates
+  // the number of sub-patches. A sub-patch is a subset of the write batch that
+  // does not have duplicate keys.
   Status WriteImpl(const WriteOptions& options, WriteBatch* updates,
                    WriteCallback* callback = nullptr,
                    uint64_t* log_used = nullptr, uint64_t log_ref = 0,
                    bool disable_memtable = false, uint64_t* seq_used = nullptr,
+                   size_t batch_cnt = 0,
                    PreReleaseCallback* pre_release_callback = nullptr);
 
   Status PipelinedWriteImpl(const WriteOptions& options, WriteBatch* updates,
@@ -685,10 +689,13 @@ class DBImpl : public DB {
                             bool disable_memtable = false,
                             uint64_t* seq_used = nullptr);
 
+  // batch_cnt is expected to be non-zero in seq_per_batch mode and indicates
+  // the number of sub-patches. A sub-patch is a subset of the write batch that
+  // does not have duplicate keys.
   Status WriteImplWALOnly(const WriteOptions& options, WriteBatch* updates,
                           WriteCallback* callback = nullptr,
                           uint64_t* log_used = nullptr, uint64_t log_ref = 0,
-                          uint64_t* seq_used = nullptr,
+                          uint64_t* seq_used = nullptr, size_t batch_cnt = 0,
                           PreReleaseCallback* pre_release_callback = nullptr);
 
   uint64_t FindMinLogContainingOutstandingPrep();
diff --git a/db/db_impl_write.cc b/db/db_impl_write.cc
index d1a2daf66c..d6a062702c 100644
--- a/db/db_impl_write.cc
+++ b/db/db_impl_write.cc
@@ -64,7 +64,9 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
                          WriteBatch* my_batch, WriteCallback* callback,
                          uint64_t* log_used, uint64_t log_ref,
                          bool disable_memtable, uint64_t* seq_used,
+                         size_t batch_cnt,
                          PreReleaseCallback* pre_release_callback) {
+  assert(!seq_per_batch_ || batch_cnt != 0);
   if (my_batch == nullptr) {
     return Status::Corruption("Batch is nullptr!");
   }
@@ -76,6 +78,7 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
         "pipelined_writes is not compatible with concurrent prepares");
   }
   if (seq_per_batch_ && immutable_db_options_.enable_pipelined_write) {
+    // TODO(yiwu): update pipeline write with seq_per_batch and batch_cnt
     return Status::NotSupported(
         "pipelined_writes is not compatible with seq_per_batch");
   }
@@ -93,7 +96,7 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
 
   if (two_write_queues_ && disable_memtable) {
     return WriteImplWALOnly(write_options, my_batch, callback, log_used,
-                            log_ref, seq_used, pre_release_callback);
+                            log_ref, seq_used, batch_cnt, pre_release_callback);
   }
 
   if (immutable_db_options_.enable_pipelined_write) {
@@ -103,7 +106,7 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
 
   PERF_TIMER_GUARD(write_pre_and_post_process_time);
   WriteThread::Writer w(write_options, my_batch, callback, log_ref,
-                        disable_memtable, pre_release_callback);
+                        disable_memtable, batch_cnt, pre_release_callback);
 
   if (!write_options.disableWAL) {
     RecordTick(stats_, WRITE_WITH_WAL);
@@ -122,7 +125,7 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
       w.status = WriteBatchInternal::InsertInto(
           &w, w.sequence, &column_family_memtables, &flush_scheduler_,
           write_options.ignore_missing_column_families, 0 /*log_number*/, this,
-          true /*concurrent_memtable_writes*/, seq_per_batch_);
+          true /*concurrent_memtable_writes*/, seq_per_batch_, w.batch_cnt);
     }
 
     if (write_thread_.CompleteParallelMemTableWriter(&w)) {
@@ -214,7 +217,7 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
     uint64_t total_byte_size = 0;
     for (auto* writer : write_group) {
       if (writer->CheckCallback(this)) {
-        valid_batches++;
+        valid_batches += writer->batch_cnt;
         if (writer->ShouldWriteToMemtable()) {
           total_count += WriteBatchInternal::Count(writer->batch);
           parallel = parallel && !writer->batch->HasMerge();
@@ -303,7 +306,8 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
           }
           writer->sequence = next_sequence;
           if (seq_per_batch_) {
-            next_sequence++;
+            assert(writer->batch_cnt);
+            next_sequence += writer->batch_cnt;
           } else if (writer->ShouldWriteToMemtable()) {
             next_sequence += WriteBatchInternal::Count(writer->batch);
           }
@@ -323,7 +327,8 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
           w.status = WriteBatchInternal::InsertInto(
               &w, w.sequence, &column_family_memtables, &flush_scheduler_,
               write_options.ignore_missing_column_families, 0 /*log_number*/,
-              this, true /*concurrent_memtable_writes*/, seq_per_batch_);
+              this, true /*concurrent_memtable_writes*/, seq_per_batch_,
+              w.batch_cnt);
         }
       }
       if (seq_used != nullptr) {
@@ -515,12 +520,13 @@ Status DBImpl::PipelinedWriteImpl(const WriteOptions& write_options,
 Status DBImpl::WriteImplWALOnly(const WriteOptions& write_options,
                                 WriteBatch* my_batch, WriteCallback* callback,
                                 uint64_t* log_used, uint64_t log_ref,
-                                uint64_t* seq_used,
+                                uint64_t* seq_used, size_t batch_cnt,
                                 PreReleaseCallback* pre_release_callback) {
   Status status;
   PERF_TIMER_GUARD(write_pre_and_post_process_time);
   WriteThread::Writer w(write_options, my_batch, callback, log_ref,
-                        true /* disable_memtable */, pre_release_callback);
+                        true /* disable_memtable */, batch_cnt,
+                        pre_release_callback);
   RecordTick(stats_, WRITE_WITH_WAL);
   StopWatch write_sw(env_, immutable_db_options_.statistics.get(), DB_WRITE);
 
@@ -576,7 +582,15 @@ Status DBImpl::WriteImplWALOnly(const WriteOptions& write_options,
   PERF_TIMER_GUARD(write_wal_time);
   // LastAllocatedSequence is increased inside WriteToWAL under
   // wal_write_mutex_ to ensure ordered events in WAL
-  size_t seq_inc = seq_per_batch_ ? write_group.size : 0 /*total_count*/;
+  size_t seq_inc = 0 /* total_count */;
+  if (seq_per_batch_) {
+    size_t total_batch_cnt = 0;
+    for (auto* writer : write_group) {
+      assert(writer->batch_cnt);
+      total_batch_cnt += writer->batch_cnt;
+    }
+    seq_inc = total_batch_cnt;
+  }
   if (!write_options.disableWAL) {
     status =
         ConcurrentWriteToWAL(write_group, log_used, &last_sequence, seq_inc);
@@ -591,7 +605,8 @@ Status DBImpl::WriteImplWALOnly(const WriteOptions& write_options,
     }
     writer->sequence = curr_seq;
     if (seq_per_batch_) {
-      curr_seq++;
+      assert(writer->batch_cnt);
+      curr_seq += writer->batch_cnt;
     }
     // else seq advances only by memtable writes
   }
diff --git a/db/write_batch.cc b/db/write_batch.cc
index 3e82f836ce..7963c326bb 100644
--- a/db/write_batch.cc
+++ b/db/write_batch.cc
@@ -402,14 +402,21 @@ Status WriteBatch::Iterate(Handler* handler) const {
   bool empty_batch = true;
   int found = 0;
   Status s;
-  while (s.ok() && !input.empty() && handler->Continue()) {
-    char tag = 0;
-    uint32_t column_family = 0;  // default
+  char tag = 0;
+  uint32_t column_family = 0;  // default
+  while ((s.ok() || s.IsTryAgain()) && !input.empty() && handler->Continue()) {
+    if (!s.IsTryAgain()) {
+      tag = 0;
+      column_family = 0;  // default
 
-    s = ReadRecordFromWriteBatch(&input, &tag, &column_family, &key, &value,
-                                 &blob, &xid);
-    if (!s.ok()) {
-      return s;
+      s = ReadRecordFromWriteBatch(&input, &tag, &column_family, &key, &value,
+                                   &blob, &xid);
+      if (!s.ok()) {
+        return s;
+      }
+    } else {
+      assert(s.IsTryAgain());
+      s = Status::OK();
     }
 
     switch (tag) {
@@ -418,47 +425,59 @@ Status WriteBatch::Iterate(Handler* handler) const {
         assert(content_flags_.load(std::memory_order_relaxed) &
                (ContentFlags::DEFERRED | ContentFlags::HAS_PUT));
         s = handler->PutCF(column_family, key, value);
-        empty_batch = false;
-        found++;
+        if (s.ok()) {
+          empty_batch = false;
+          found++;
+        }
         break;
       case kTypeColumnFamilyDeletion:
       case kTypeDeletion:
         assert(content_flags_.load(std::memory_order_relaxed) &
                (ContentFlags::DEFERRED | ContentFlags::HAS_DELETE));
         s = handler->DeleteCF(column_family, key);
-        empty_batch = false;
-        found++;
+        if (s.ok()) {
+          empty_batch = false;
+          found++;
+        }
         break;
       case kTypeColumnFamilySingleDeletion:
       case kTypeSingleDeletion:
         assert(content_flags_.load(std::memory_order_relaxed) &
                (ContentFlags::DEFERRED | ContentFlags::HAS_SINGLE_DELETE));
         s = handler->SingleDeleteCF(column_family, key);
-        empty_batch = false;
-        found++;
+        if (s.ok()) {
+          empty_batch = false;
+          found++;
+        }
         break;
       case kTypeColumnFamilyRangeDeletion:
       case kTypeRangeDeletion:
         assert(content_flags_.load(std::memory_order_relaxed) &
                (ContentFlags::DEFERRED | ContentFlags::HAS_DELETE_RANGE));
         s = handler->DeleteRangeCF(column_family, key, value);
-        empty_batch = false;
-        found++;
+        if (s.ok()) {
+          empty_batch = false;
+          found++;
+        }
         break;
       case kTypeColumnFamilyMerge:
       case kTypeMerge:
         assert(content_flags_.load(std::memory_order_relaxed) &
                (ContentFlags::DEFERRED | ContentFlags::HAS_MERGE));
         s = handler->MergeCF(column_family, key, value);
-        empty_batch = false;
-        found++;
+        if (s.ok()) {
+          empty_batch = false;
+          found++;
+        }
         break;
       case kTypeColumnFamilyBlobIndex:
       case kTypeBlobIndex:
         assert(content_flags_.load(std::memory_order_relaxed) &
                (ContentFlags::DEFERRED | ContentFlags::HAS_BLOB_INDEX));
         s = handler->PutBlobIndexCF(column_family, key, value);
-        found++;
+        if (s.ok()) {
+          found++;
+        }
         break;
       case kTypeLogData:
         handler->LogData(blob);
@@ -1084,12 +1103,23 @@ class MemTableInserter : public WriteBatch::Handler {
       MaybeAdvanceSeq();
       return seek_status;
     }
+    Status ret_status;
 
     MemTable* mem = cf_mems_->GetMemTable();
     auto* moptions = mem->GetImmutableMemTableOptions();
+    // inplace_update_support is inconsistent with snapshots, and therefore with
+    // any kind of transactions including the ones that use seq_per_batch
+    assert(!seq_per_batch_ || !moptions->inplace_update_support);
     if (!moptions->inplace_update_support) {
-      mem->Add(sequence_, value_type, key, value, concurrent_memtable_writes_,
-               get_post_process_info(mem));
+      bool mem_res =
+          mem->Add(sequence_, value_type, key, value,
+                   concurrent_memtable_writes_, get_post_process_info(mem));
+      if (!mem_res) {
+        assert(seq_per_batch_);
+        ret_status = Status::TryAgain("key+seq exists");
+        const bool BATCH_BOUNDRY = true;
+        MaybeAdvanceSeq(BATCH_BOUNDRY);
+      }
     } else if (moptions->inplace_callback == nullptr) {
       assert(!concurrent_memtable_writes_);
       mem->Update(sequence_, key, value);
@@ -1125,11 +1155,15 @@ class MemTableInserter : public WriteBatch::Handler {
                                                  value, &merged_value);
         if (status == UpdateStatus::UPDATED_INPLACE) {
           // prev_value is updated in-place with final value.
-          mem->Add(sequence_, value_type, key, Slice(prev_buffer, prev_size));
+          bool mem_res __attribute__((__unused__)) = mem->Add(
+              sequence_, value_type, key, Slice(prev_buffer, prev_size));
+          assert(mem_res);
           RecordTick(moptions->statistics, NUMBER_KEYS_WRITTEN);
         } else if (status == UpdateStatus::UPDATED) {
           // merged_value contains the final value.
-          mem->Add(sequence_, value_type, key, Slice(merged_value));
+          bool mem_res __attribute__((__unused__)) =
+              mem->Add(sequence_, value_type, key, Slice(merged_value));
+          assert(mem_res);
           RecordTick(moptions->statistics, NUMBER_KEYS_WRITTEN);
         }
       }
@@ -1139,7 +1173,7 @@ class MemTableInserter : public WriteBatch::Handler {
     // in memtable add/update.
     MaybeAdvanceSeq();
     CheckMemtableFull();
-    return Status::OK();
+    return ret_status;
   }
 
   virtual Status PutCF(uint32_t column_family_id, const Slice& key,
@@ -1149,12 +1183,20 @@ class MemTableInserter : public WriteBatch::Handler {
 
   Status DeleteImpl(uint32_t column_family_id, const Slice& key,
                     const Slice& value, ValueType delete_type) {
+    Status ret_status;
     MemTable* mem = cf_mems_->GetMemTable();
-    mem->Add(sequence_, delete_type, key, value, concurrent_memtable_writes_,
-             get_post_process_info(mem));
+    bool mem_res =
+        mem->Add(sequence_, delete_type, key, value,
+                 concurrent_memtable_writes_, get_post_process_info(mem));
+    if (!mem_res) {
+      assert(seq_per_batch_);
+      ret_status = Status::TryAgain("key+seq exists");
+      const bool BATCH_BOUNDRY = true;
+      MaybeAdvanceSeq(BATCH_BOUNDRY);
+    }
     MaybeAdvanceSeq();
     CheckMemtableFull();
-    return Status::OK();
+    return ret_status;
   }
 
   virtual Status DeleteCF(uint32_t column_family_id,
@@ -1246,6 +1288,7 @@ class MemTableInserter : public WriteBatch::Handler {
       return seek_status;
     }
 
+    Status ret_status;
     MemTable* mem = cf_mems_->GetMemTable();
     auto* moptions = mem->GetImmutableMemTableOptions();
     bool perform_merge = false;
@@ -1301,18 +1344,30 @@ class MemTableInserter : public WriteBatch::Handler {
         perform_merge = false;
       } else {
         // 3) Add value to memtable
-        mem->Add(sequence_, kTypeValue, key, new_value);
+        bool mem_res = mem->Add(sequence_, kTypeValue, key, new_value);
+        if (!mem_res) {
+          assert(seq_per_batch_);
+          ret_status = Status::TryAgain("key+seq exists");
+          const bool BATCH_BOUNDRY = true;
+          MaybeAdvanceSeq(BATCH_BOUNDRY);
+        }
       }
     }
 
     if (!perform_merge) {
       // Add merge operator to memtable
-      mem->Add(sequence_, kTypeMerge, key, value);
+      bool mem_res = mem->Add(sequence_, kTypeMerge, key, value);
+      if (!mem_res) {
+        assert(seq_per_batch_);
+        ret_status = Status::TryAgain("key+seq exists");
+        const bool BATCH_BOUNDRY = true;
+        MaybeAdvanceSeq(BATCH_BOUNDRY);
+      }
     }
 
     MaybeAdvanceSeq();
     CheckMemtableFull();
-    return Status::OK();
+    return ret_status;
   }
 
   virtual Status PutBlobIndexCF(uint32_t column_family_id, const Slice& key,
@@ -1496,6 +1551,8 @@ Status WriteBatchInternal::InsertInto(
     if (!w->status.ok()) {
       return w->status;
     }
+    assert(!seq_per_batch || w->batch_cnt != 0);
+    assert(!seq_per_batch || inserter.sequence() - w->sequence == w->batch_cnt);
   }
   return Status::OK();
 }
@@ -1504,7 +1561,7 @@ Status WriteBatchInternal::InsertInto(
     WriteThread::Writer* writer, SequenceNumber sequence,
     ColumnFamilyMemTables* memtables, FlushScheduler* flush_scheduler,
     bool ignore_missing_column_families, uint64_t log_number, DB* db,
-    bool concurrent_memtable_writes, bool seq_per_batch) {
+    bool concurrent_memtable_writes, bool seq_per_batch, size_t batch_cnt) {
   assert(writer->ShouldWriteToMemtable());
   MemTableInserter inserter(sequence, memtables, flush_scheduler,
                             ignore_missing_column_families, log_number, db,
@@ -1513,6 +1570,8 @@ Status WriteBatchInternal::InsertInto(
   SetSequence(writer->batch, sequence);
   inserter.set_log_number_ref(writer->log_ref);
   Status s = writer->batch->Iterate(&inserter);
+  assert(!seq_per_batch || batch_cnt != 0);
+  assert(!seq_per_batch || inserter.sequence() - sequence == batch_cnt);
   if (concurrent_memtable_writes) {
     inserter.PostProcess();
   }
diff --git a/db/write_batch_internal.h b/db/write_batch_internal.h
index a352fc89c1..aeaf0e1ea9 100644
--- a/db/write_batch_internal.h
+++ b/db/write_batch_internal.h
@@ -182,7 +182,7 @@ class WriteBatchInternal {
                            bool ignore_missing_column_families = false,
                            uint64_t log_number = 0, DB* db = nullptr,
                            bool concurrent_memtable_writes = false,
-                           bool seq_per_batch = false);
+                           bool seq_per_batch = false, size_t batch_cnt = 0);
 
   static Status Append(WriteBatch* dst, const WriteBatch* src,
                        const bool WAL_only = false);
diff --git a/db/write_callback_test.cc b/db/write_callback_test.cc
index 036d51293c..7d04d50173 100644
--- a/db/write_callback_test.cc
+++ b/db/write_callback_test.cc
@@ -291,7 +291,7 @@ TEST_F(WriteCallbackTest, WriteWithCallbackTest) {
                 woptions.disableWAL = !enable_WAL;
                 woptions.sync = enable_WAL;
                 Status s;
-                if (seq_per_batch && two_queues) {
+                if (seq_per_batch) {
                   class PublishSeqCallback : public PreReleaseCallback {
                    public:
                     PublishSeqCallback(DBImpl* db_impl_in)
@@ -302,9 +302,13 @@ TEST_F(WriteCallbackTest, WriteWithCallbackTest) {
                     }
                     DBImpl* db_impl_;
                   } publish_seq_callback(db_impl);
-                  s = db_impl->WriteImpl(woptions, &write_op.write_batch_,
-                                         &write_op.callback_, nullptr, 0, false,
-                                         nullptr, &publish_seq_callback);
+                  // seq_per_batch requires a natural batch separator or Noop
+                  WriteBatchInternal::InsertNoop(&write_op.write_batch_);
+                  const size_t ONE_BATCH = 1;
+                  s = db_impl->WriteImpl(
+                      woptions, &write_op.write_batch_, &write_op.callback_,
+                      nullptr, 0, false, nullptr, ONE_BATCH,
+                      two_queues ? &publish_seq_callback : nullptr);
                 } else {
                   s = db_impl->WriteWithCallback(
                       woptions, &write_op.write_batch_, &write_op.callback_);
diff --git a/db/write_thread.h b/db/write_thread.h
index 3d5e2f9e6e..518b542992 100644
--- a/db/write_thread.h
+++ b/db/write_thread.h
@@ -118,6 +118,7 @@ class WriteThread {
     bool no_slowdown;
     bool disable_wal;
     bool disable_memtable;
+    size_t batch_cnt;  // if non-zero, number of sub-batches in the write batch
     PreReleaseCallback* pre_release_callback;
     uint64_t log_used;  // log number that this batch was inserted into
     uint64_t log_ref;   // log number that memtable insert should reference
@@ -128,6 +129,7 @@ class WriteThread {
     SequenceNumber sequence;  // the sequence number to use for the first key
     Status status;            // status of memtable inserter
     Status callback_status;   // status returned by callback->Callback()
+
     std::aligned_storage<sizeof(std::mutex)>::type state_mutex_bytes;
     std::aligned_storage<sizeof(std::condition_variable)>::type state_cv_bytes;
     Writer* link_older;  // read/write only before linking, or as leader
@@ -139,6 +141,7 @@ class WriteThread {
           no_slowdown(false),
           disable_wal(false),
           disable_memtable(false),
+          batch_cnt(0),
           pre_release_callback(nullptr),
           log_used(0),
           log_ref(0),
@@ -152,12 +155,14 @@ class WriteThread {
 
     Writer(const WriteOptions& write_options, WriteBatch* _batch,
            WriteCallback* _callback, uint64_t _log_ref, bool _disable_memtable,
+           size_t _batch_cnt = 0,
            PreReleaseCallback* _pre_release_callback = nullptr)
         : batch(_batch),
           sync(write_options.sync),
           no_slowdown(write_options.no_slowdown),
           disable_wal(write_options.disableWAL),
           disable_memtable(_disable_memtable),
+          batch_cnt(_batch_cnt),
           pre_release_callback(_pre_release_callback),
           log_used(0),
           log_ref(_log_ref),
diff --git a/include/rocksdb/utilities/write_batch_with_index.h b/include/rocksdb/utilities/write_batch_with_index.h
index f49cb3888c..84b2938157 100644
--- a/include/rocksdb/utilities/write_batch_with_index.h
+++ b/include/rocksdb/utilities/write_batch_with_index.h
@@ -228,13 +228,8 @@ class WriteBatchWithIndex : public WriteBatchBase {
 
  private:
   friend class WritePreparedTxn;
-  // TODO(myabandeh): this is hackish, non-efficient solution to enable the e2e
-  // unit tests. Replace it with a proper solution. Collapse the WriteBatch to
-  // remove the duplicate keys. The index will not be updated after this.
-  // Returns false if collapse was not necessary
-  bool Collapse();
-  void DisableDuplicateMergeKeys() { allow_dup_merge_ = false; }
-  bool allow_dup_merge_ = true;
+  // Returns true if there has been duplicate keys in the batch.
+  bool HasDuplicateKeys();
 
   Status GetFromBatchAndDB(DB* db, const ReadOptions& read_options,
                            ColumnFamilyHandle* column_family, const Slice& key,
diff --git a/utilities/transactions/pessimistic_transaction.cc b/utilities/transactions/pessimistic_transaction.cc
index 203dd2071c..3a7d801aa8 100644
--- a/utilities/transactions/pessimistic_transaction.cc
+++ b/utilities/transactions/pessimistic_transaction.cc
@@ -307,7 +307,7 @@ Status WriteCommittedTxn::CommitWithoutPrepareInternal() {
   return s;
 }
 
-Status WriteCommittedTxn::CommitBatchInternal(WriteBatch* batch) {
+Status WriteCommittedTxn::CommitBatchInternal(WriteBatch* batch, size_t) {
   Status s = db_->Write(write_options_, batch);
   return s;
 }
diff --git a/utilities/transactions/pessimistic_transaction.h b/utilities/transactions/pessimistic_transaction.h
index 51776b8001..0434a69db8 100644
--- a/utilities/transactions/pessimistic_transaction.h
+++ b/utilities/transactions/pessimistic_transaction.h
@@ -121,7 +121,10 @@ class PessimisticTransaction : public TransactionBaseImpl {
 
   virtual Status CommitWithoutPrepareInternal() = 0;
 
-  virtual Status CommitBatchInternal(WriteBatch* batch) = 0;
+  // batch_cnt if non-zero is the number of sub-batches. A sub-batch is a batch
+  // with no duplicate keys. If zero, then the number of sub-batches is unknown.
+  virtual Status CommitBatchInternal(WriteBatch* batch,
+                                     size_t batch_cnt = 0) = 0;
 
   virtual Status CommitInternal() = 0;
 
@@ -204,7 +207,7 @@ class WriteCommittedTxn : public PessimisticTransaction {
 
   Status CommitWithoutPrepareInternal() override;
 
-  Status CommitBatchInternal(WriteBatch* batch) override;
+  Status CommitBatchInternal(WriteBatch* batch, size_t batch_cnt) override;
 
   Status CommitInternal() override;
 
diff --git a/utilities/transactions/pessimistic_transaction_db.cc b/utilities/transactions/pessimistic_transaction_db.cc
index 9fff27e77c..0aad76a502 100644
--- a/utilities/transactions/pessimistic_transaction_db.cc
+++ b/utilities/transactions/pessimistic_transaction_db.cc
@@ -82,12 +82,29 @@ PessimisticTransactionDB::~PessimisticTransactionDB() {
   }
 }
 
+Status PessimisticTransactionDB::VerifyCFOptions(const ColumnFamilyOptions&) {
+  return Status::OK();
+}
+
 Status PessimisticTransactionDB::Initialize(
     const std::vector<size_t>& compaction_enabled_cf_indices,
     const std::vector<ColumnFamilyHandle*>& handles) {
   for (auto cf_ptr : handles) {
     AddColumnFamily(cf_ptr);
   }
+  // Verify cf options
+  for (auto handle : handles) {
+    ColumnFamilyDescriptor cfd;
+    Status s = handle->GetDescriptor(&cfd);
+    if (!s.ok()) {
+      return s;
+    }
+    s = VerifyCFOptions(cfd.options);
+    if (!s.ok()) {
+      return s;
+    }
+  }
+
   // Re-enable compaction for the column families that initially had
   // compaction enabled.
   std::vector<ColumnFamilyHandle*> compaction_enabled_cf_handles;
@@ -158,6 +175,30 @@ TransactionDBOptions PessimisticTransactionDB::ValidateTxnDBOptions(
   return validated;
 }
 
+void PessimisticTransactionDB::UpdateCFComparatorMap(
+    const std::vector<ColumnFamilyHandle*>& handles) {
+  auto cf_map = new std::map<uint32_t, const Comparator*>();
+  for (auto h : handles) {
+    auto id = h->GetID();
+    const Comparator* comparator = h->GetComparator();
+    (*cf_map)[id] = comparator;
+  }
+  cf_map_.store(cf_map);
+  cf_map_gc_.reset(cf_map);
+}
+
+void PessimisticTransactionDB::UpdateCFComparatorMap(
+    const ColumnFamilyHandle* h) {
+  auto old_cf_map_ptr = cf_map_.load();
+  assert(old_cf_map_ptr);
+  auto cf_map = new std::map<uint32_t, const Comparator*>(*old_cf_map_ptr);
+  auto id = h->GetID();
+  const Comparator* comparator = h->GetComparator();
+  (*cf_map)[id] = comparator;
+  cf_map_.store(cf_map);
+  cf_map_gc_.reset(cf_map);
+}
+
 Status TransactionDB::Open(const Options& options,
                            const TransactionDBOptions& txn_db_options,
                            const std::string& dbname, TransactionDB** dbptr) {
@@ -245,6 +286,7 @@ Status TransactionDB::WrapDB(
       txn_db = new WriteCommittedTxnDB(
           db, PessimisticTransactionDB::ValidateTxnDBOptions(txn_db_options));
   }
+  txn_db->UpdateCFComparatorMap(handles);
   *dbptr = txn_db;
   Status s = txn_db->Initialize(compaction_enabled_cf_indices, handles);
   return s;
@@ -270,6 +312,7 @@ Status TransactionDB::WrapStackableDB(
       txn_db = new WriteCommittedTxnDB(
           db, PessimisticTransactionDB::ValidateTxnDBOptions(txn_db_options));
   }
+  txn_db->UpdateCFComparatorMap(handles);
   *dbptr = txn_db;
   Status s = txn_db->Initialize(compaction_enabled_cf_indices, handles);
   return s;
@@ -286,10 +329,15 @@ Status PessimisticTransactionDB::CreateColumnFamily(
     const ColumnFamilyOptions& options, const std::string& column_family_name,
     ColumnFamilyHandle** handle) {
   InstrumentedMutexLock l(&column_family_mutex_);
+  Status s = VerifyCFOptions(options);
+  if (!s.ok()) {
+    return s;
+  }
 
-  Status s = db_->CreateColumnFamily(options, column_family_name, handle);
+  s = db_->CreateColumnFamily(options, column_family_name, handle);
   if (s.ok()) {
     lock_mgr_.AddColumnFamily((*handle)->GetID());
+    UpdateCFComparatorMap(*handle);
   }
 
   return s;
@@ -439,8 +487,6 @@ Status PessimisticTransactionDB::Write(const WriteOptions& opts,
   // concurrent transactions.
   Transaction* txn = BeginInternalTransaction(opts);
   txn->DisableIndexing();
-  // TODO(myabandeh): indexing being disabled we need another machanism to
-  // detect duplicattes in the input patch
 
   auto txn_impl =
       static_cast_with_check<PessimisticTransaction, Transaction>(txn);
diff --git a/utilities/transactions/pessimistic_transaction_db.h b/utilities/transactions/pessimistic_transaction_db.h
index 4311e88c35..9b4ad5618e 100644
--- a/utilities/transactions/pessimistic_transaction_db.h
+++ b/utilities/transactions/pessimistic_transaction_db.h
@@ -113,15 +113,27 @@ class PessimisticTransactionDB : public TransactionDB {
   std::vector<DeadlockPath> GetDeadlockInfoBuffer() override;
   void SetDeadlockInfoBufferSize(uint32_t target_size) override;
 
+  void UpdateCFComparatorMap(const std::vector<ColumnFamilyHandle*>& handles);
+  void UpdateCFComparatorMap(const ColumnFamilyHandle* handle);
+  std::map<uint32_t, const Comparator*>* GetCFComparatorMap() {
+    return cf_map_.load();
+  }
+
  protected:
   DBImpl* db_impl_;
   std::shared_ptr<Logger> info_log_;
   const TransactionDBOptions txn_db_options_;
+  // A cache of the cf comparators
+  std::atomic<std::map<uint32_t, const Comparator*>*> cf_map_;
+  // GC of the object above
+  std::unique_ptr<std::map<uint32_t, const Comparator*>> cf_map_gc_;
 
   void ReinitializeTransaction(
       Transaction* txn, const WriteOptions& write_options,
       const TransactionOptions& txn_options = TransactionOptions());
 
+  virtual Status VerifyCFOptions(const ColumnFamilyOptions& cf_options);
+
  private:
   friend class WritePreparedTxnDB;
   friend class WritePreparedTxnDBMock;
diff --git a/utilities/transactions/transaction_base.h b/utilities/transactions/transaction_base.h
index 05dca1da4a..d336eb3a78 100644
--- a/utilities/transactions/transaction_base.h
+++ b/utilities/transactions/transaction_base.h
@@ -232,7 +232,7 @@ class TransactionBaseImpl : public Transaction {
 
   // iterates over the given batch and makes the appropriate inserts.
   // used for rebuilding prepared transactions after recovery.
-  Status RebuildFromWriteBatch(WriteBatch* src_batch) override;
+  virtual Status RebuildFromWriteBatch(WriteBatch* src_batch) override;
 
   WriteBatch* GetCommitTimeWriteBatch() override;
 
diff --git a/utilities/transactions/transaction_test.cc b/utilities/transactions/transaction_test.cc
index 129e9f5764..d80dd05d04 100644
--- a/utilities/transactions/transaction_test.cc
+++ b/utilities/transactions/transaction_test.cc
@@ -70,6 +70,25 @@ TEST_P(TransactionTest, DoubleEmptyWrite) {
 
   ASSERT_OK(db->Write(write_options, &batch));
   ASSERT_OK(db->Write(write_options, &batch));
+
+  // Also test committing empty transactions in 2PC
+  TransactionOptions txn_options;
+  Transaction* txn0 = db->BeginTransaction(write_options, txn_options);
+  ASSERT_OK(txn0->SetName("xid"));
+  ASSERT_OK(txn0->Prepare());
+  ASSERT_OK(txn0->Commit());
+  delete txn0;
+
+  // Also test that it works during recovery
+  txn0 = db->BeginTransaction(write_options, txn_options);
+  ASSERT_OK(txn0->SetName("xid2"));
+  txn0->Put(Slice("foo0"), Slice("bar0a"));
+  ASSERT_OK(txn0->Prepare());
+  delete txn0;
+  ASSERT_OK(ReOpenNoDelete());
+  txn0 = db->GetTransactionByName("xid2");
+  ASSERT_OK(txn0->Commit());
+  delete txn0;
 }
 
 TEST_P(TransactionTest, SuccessTest) {
@@ -2874,12 +2893,8 @@ TEST_P(TransactionTest, UntrackedWrites) {
   // Untracked writes should succeed even though key was written after snapshot
   s = txn->PutUntracked("untracked", "1");
   ASSERT_OK(s);
-  if (txn_db_options.write_policy != WRITE_PREPARED) {
-    // WRITE_PREPARED does not currently support dup merge keys.
-    // TODO(myabandeh): remove this if-then when the support is added
-    s = txn->MergeUntracked("untracked", "2");
-    ASSERT_OK(s);
-  }
+  s = txn->MergeUntracked("untracked", "2");
+  ASSERT_OK(s);
   s = txn->DeleteUntracked("untracked");
   ASSERT_OK(s);
 
@@ -4250,11 +4265,6 @@ TEST_P(TransactionTest, SingleDeleteTest) {
 }
 
 TEST_P(TransactionTest, MergeTest) {
-  if (txn_db_options.write_policy == WRITE_PREPARED) {
-    // WRITE_PREPARED does not currently support dup merge keys.
-    // TODO(myabandeh): remove this if-then when the support is added
-    return;
-  }
   WriteOptions write_options;
   ReadOptions read_options;
   string value;
@@ -4978,65 +4988,273 @@ TEST_P(TransactionTest, SeqAdvanceTest) {
 }
 
 // Test that the transactional db can handle duplicate keys in the write batch
-TEST_P(TransactionTest, DuplicateKeyTest) {
+TEST_P(TransactionTest, DuplicateKeys) {
+  ColumnFamilyOptions cf_options;
+  std::string cf_name = "two";
+  ColumnFamilyHandle* cf_handle = nullptr;
+  {
+    db->CreateColumnFamily(cf_options, cf_name, &cf_handle);
+    WriteOptions write_options;
+    WriteBatch batch;
+    batch.Put(Slice("key"), Slice("value"));
+    batch.Put(Slice("key2"), Slice("value2"));
+    // duplicate the keys
+    batch.Put(Slice("key"), Slice("value3"));
+    // duplicate the 2nd key. It should not be counted duplicate since a
+    // sub-patch is cut after the last duplicate.
+    batch.Put(Slice("key2"), Slice("value4"));
+    // duplicate the keys but in a different cf. It should not be counted as
+    // duplicate keys
+    batch.Put(cf_handle, Slice("key"), Slice("value5"));
+
+    ASSERT_OK(db->Write(write_options, &batch));
+
+    ReadOptions ropt;
+    PinnableSlice pinnable_val;
+    auto s = db->Get(ropt, db->DefaultColumnFamily(), "key", &pinnable_val);
+    ASSERT_OK(s);
+    ASSERT_TRUE(pinnable_val == ("value3"));
+    s = db->Get(ropt, db->DefaultColumnFamily(), "key2", &pinnable_val);
+    ASSERT_OK(s);
+    ASSERT_TRUE(pinnable_val == ("value4"));
+    s = db->Get(ropt, cf_handle, "key", &pinnable_val);
+    ASSERT_OK(s);
+    ASSERT_TRUE(pinnable_val == ("value5"));
+
+    delete cf_handle;
+  }
+
+  // Test with non-bytewise comparator
+  {
+    // A comparator that uses only the first three bytes
+    class ThreeBytewiseComparator : public Comparator {
+     public:
+      ThreeBytewiseComparator() {}
+      virtual const char* Name() const override {
+        return "test.ThreeBytewiseComparator";
+      }
+      virtual int Compare(const Slice& a, const Slice& b) const override {
+        Slice na = Slice(a.data(), a.size() < 3 ? a.size() : 3);
+        Slice nb = Slice(b.data(), b.size() < 3 ? b.size() : 3);
+        return na.compare(nb);
+      }
+      virtual bool Equal(const Slice& a, const Slice& b) const override {
+        Slice na = Slice(a.data(), a.size() < 3 ? a.size() : 3);
+        Slice nb = Slice(b.data(), b.size() < 3 ? b.size() : 3);
+        return na == nb;
+      }
+      // This methods below dont seem relevant to this test. Implement them if
+      // proven othersize.
+      void FindShortestSeparator(std::string* start,
+                                 const Slice& limit) const override {
+        const Comparator* bytewise_comp = BytewiseComparator();
+        bytewise_comp->FindShortestSeparator(start, limit);
+      }
+      void FindShortSuccessor(std::string* key) const override {
+        const Comparator* bytewise_comp = BytewiseComparator();
+        bytewise_comp->FindShortSuccessor(key);
+      }
+    };
+    ReOpen();
+    std::unique_ptr<const Comparator> comp_gc(new ThreeBytewiseComparator());
+    cf_options.comparator = comp_gc.get();
+    ASSERT_OK(db->CreateColumnFamily(cf_options, cf_name, &cf_handle));
+    WriteOptions write_options;
+    WriteBatch batch;
+    batch.Put(cf_handle, Slice("key"), Slice("value"));
+    // The first three bytes are the same, do it must be counted as duplicate
+    batch.Put(cf_handle, Slice("key2"), Slice("value2"));
+    ASSERT_OK(db->Write(write_options, &batch));
+
+    // The value must be the most recent value for all the keys equal to "key",
+    // including "key2"
+    ReadOptions ropt;
+    PinnableSlice pinnable_val;
+    ASSERT_OK(db->Get(ropt, cf_handle, "key", &pinnable_val));
+    ASSERT_TRUE(pinnable_val == ("value2"));
+
+    // Test duplicate keys with rollback
+    TransactionOptions txn_options;
+    Transaction* txn0 = db->BeginTransaction(write_options, txn_options);
+    ASSERT_OK(txn0->SetName("xid"));
+    ASSERT_OK(txn0->Put(cf_handle, Slice("key3"), Slice("value3")));
+    ASSERT_OK(txn0->Merge(cf_handle, Slice("key4"), Slice("value4")));
+    ASSERT_OK(txn0->Rollback());
+    ASSERT_OK(db->Get(ropt, cf_handle, "key5", &pinnable_val));
+    ASSERT_TRUE(pinnable_val == ("value2"));
+    delete txn0;
+
+    delete cf_handle;
+    cf_options.comparator = BytewiseComparator();
+  }
+
   for (bool do_prepare : {true, false}) {
+    for (bool do_rollback : {true, false}) {
+      for (bool with_commit_batch : {true, false}) {
+        if (with_commit_batch && !do_prepare) {
+          continue;
+        }
+        if (with_commit_batch && do_rollback) {
+          continue;
+        }
+        ReOpen();
+        db->CreateColumnFamily(cf_options, cf_name, &cf_handle);
+        TransactionOptions txn_options;
+        txn_options.use_only_the_last_commit_time_batch_for_recovery = false;
+        WriteOptions write_options;
+        Transaction* txn0 = db->BeginTransaction(write_options, txn_options);
+        auto s = txn0->SetName("xid");
+        ASSERT_OK(s);
+        s = txn0->Put(Slice("foo0"), Slice("bar0a"));
+        ASSERT_OK(s);
+        s = txn0->Put(Slice("foo0"), Slice("bar0b"));
+        ASSERT_OK(s);
+        s = txn0->Put(Slice("foo1"), Slice("bar1"));
+        ASSERT_OK(s);
+        s = txn0->Merge(Slice("foo2"), Slice("bar2a"));
+        ASSERT_OK(s);
+        // Repeat a key after the start of a sub-patch. This should not cause a
+        // duplicate in the most recent sub-patch and hence not creating a new
+        // sub-patch.
+        s = txn0->Put(Slice("foo0"), Slice("bar0c"));
+        ASSERT_OK(s);
+        s = txn0->Merge(Slice("foo2"), Slice("bar2b"));
+        ASSERT_OK(s);
+        // duplicate the keys but in a different cf. It should not be counted as
+        // duplicate.
+        s = txn0->Put(cf_handle, Slice("foo0"), Slice("bar0-cf1"));
+        ASSERT_OK(s);
+        s = txn0->Put(Slice("foo3"), Slice("bar3"));
+        ASSERT_OK(s);
+        s = txn0->Merge(Slice("foo3"), Slice("bar3"));
+        ASSERT_OK(s);
+        s = txn0->Put(Slice("foo4"), Slice("bar4"));
+        ASSERT_OK(s);
+        s = txn0->Delete(Slice("foo4"));
+        ASSERT_OK(s);
+        s = txn0->SingleDelete(Slice("foo4"));
+        ASSERT_OK(s);
+        if (do_prepare) {
+          s = txn0->Prepare();
+          ASSERT_OK(s);
+        }
+        if (do_rollback) {
+          // Test rolling back the batch with duplicates
+          s = txn0->Rollback();
+          ASSERT_OK(s);
+        } else {
+          if (with_commit_batch) {
+            assert(do_prepare);
+            auto cb = txn0->GetCommitTimeWriteBatch();
+            // duplicate a key in the original batch
+            // TODO(myabandeh): the behavior of GetCommitTimeWriteBatch
+            // conflicting with the prepared batch is currently undefined and
+            // gives different results in different implementations.
+
+            // s = cb->Put(Slice("foo0"), Slice("bar0d"));
+            // ASSERT_OK(s);
+            // add a new duplicate key
+            s = cb->Put(Slice("foo6"), Slice("bar6a"));
+            ASSERT_OK(s);
+            s = cb->Put(Slice("foo6"), Slice("bar6b"));
+            ASSERT_OK(s);
+            // add a duplicate key that is removed in the same batch
+            s = cb->Put(Slice("foo7"), Slice("bar7a"));
+            ASSERT_OK(s);
+            s = cb->Delete(Slice("foo7"));
+            ASSERT_OK(s);
+          }
+          s = txn0->Commit();
+          ASSERT_OK(s);
+        }
+        if (!do_prepare && !do_rollback) {
+          auto pdb = reinterpret_cast<PessimisticTransactionDB*>(db);
+          pdb->UnregisterTransaction(txn0);
+        }
+        delete txn0;
+        ReadOptions ropt;
+        PinnableSlice pinnable_val;
+
+        if (do_rollback) {
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo0", &pinnable_val);
+          ASSERT_TRUE(s.IsNotFound());
+          s = db->Get(ropt, cf_handle, "foo0", &pinnable_val);
+          ASSERT_TRUE(s.IsNotFound());
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo1", &pinnable_val);
+          ASSERT_TRUE(s.IsNotFound());
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo2", &pinnable_val);
+          ASSERT_TRUE(s.IsNotFound());
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo3", &pinnable_val);
+          ASSERT_TRUE(s.IsNotFound());
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo4", &pinnable_val);
+          ASSERT_TRUE(s.IsNotFound());
+        } else {
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo0", &pinnable_val);
+          ASSERT_OK(s);
+          ASSERT_TRUE(pinnable_val == ("bar0c"));
+          s = db->Get(ropt, cf_handle, "foo0", &pinnable_val);
+          ASSERT_OK(s);
+          ASSERT_TRUE(pinnable_val == ("bar0-cf1"));
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo1", &pinnable_val);
+          ASSERT_OK(s);
+          ASSERT_TRUE(pinnable_val == ("bar1"));
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo2", &pinnable_val);
+          ASSERT_OK(s);
+          ASSERT_TRUE(pinnable_val == ("bar2a,bar2b"));
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo3", &pinnable_val);
+          ASSERT_OK(s);
+          ASSERT_TRUE(pinnable_val == ("bar3,bar3"));
+          s = db->Get(ropt, db->DefaultColumnFamily(), "foo4", &pinnable_val);
+          ASSERT_TRUE(s.IsNotFound());
+          if (with_commit_batch) {
+            s = db->Get(ropt, db->DefaultColumnFamily(), "foo6", &pinnable_val);
+            ASSERT_OK(s);
+            ASSERT_TRUE(pinnable_val == ("bar6b"));
+            s = db->Get(ropt, db->DefaultColumnFamily(), "foo7", &pinnable_val);
+            ASSERT_TRUE(s.IsNotFound());
+          }
+        }
+        delete cf_handle;
+      }  // with_commit_batch
+    }    // do_rollback
+  }      // do_prepare
+
+  {
+    // Also test with max_successive_merges > 0. max_successive_merges will not
+    // affect our algorithm for duplicate key insertion but we add the test to
+    // verify that.
+    cf_options.max_successive_merges = 2;
+    cf_options.merge_operator = MergeOperators::CreateStringAppendOperator();
+    ReOpen();
+    db->CreateColumnFamily(cf_options, cf_name, &cf_handle);
+    WriteOptions write_options;
+    // Ensure one value for the key
+    db->Put(write_options, cf_handle, Slice("key"), Slice("value"));
+    WriteBatch batch;
+    // Merge more than max_successive_merges times
+    batch.Merge(cf_handle, Slice("key"), Slice("1"));
+    batch.Merge(cf_handle, Slice("key"), Slice("2"));
+    batch.Merge(cf_handle, Slice("key"), Slice("3"));
+    batch.Merge(cf_handle, Slice("key"), Slice("4"));
+    ASSERT_OK(db->Write(write_options, &batch));
+    ReadOptions read_options;
+    string value;
+    ASSERT_OK(db->Get(read_options, cf_handle, "key", &value));
+    ASSERT_EQ(value, "value,1,2,3,4");
+    delete cf_handle;
+  }
+
+  {
+    // Test that the duplicate detection is not compromised after rolling back
+    // to a save point
     TransactionOptions txn_options;
     WriteOptions write_options;
     Transaction* txn0 = db->BeginTransaction(write_options, txn_options);
-    auto s = txn0->SetName("xid");
-    ASSERT_OK(s);
-    s = txn0->Put(Slice("foo0"), Slice("bar0a"));
-    ASSERT_OK(s);
-    s = txn0->Put(Slice("foo0"), Slice("bar0b"));
-    ASSERT_OK(s);
-    s = txn0->Put(Slice("foo1"), Slice("bar1"));
-    ASSERT_OK(s);
-    s = txn0->Merge(Slice("foo2"), Slice("bar2a"));
-    ASSERT_OK(s);
-    // TODO(myabandeh): enable this after duplicatae merge keys are supported
-    // s = txn0->Merge(Slice("foo2"), Slice("bar2a"));
-    // ASSERT_OK(s);
-    s = txn0->Put(Slice("foo2"), Slice("bar2b"));
-    ASSERT_OK(s);
-    s = txn0->Put(Slice("foo3"), Slice("bar3"));
-    ASSERT_OK(s);
-    // TODO(myabandeh): enable this after duplicatae merge keys are supported
-    // s = txn0->Merge(Slice("foo3"), Slice("bar3"));
-    // ASSERT_OK(s);
-    s = txn0->Put(Slice("foo4"), Slice("bar4"));
-    ASSERT_OK(s);
-    s = txn0->Delete(Slice("foo4"));
-    ASSERT_OK(s);
-    s = txn0->SingleDelete(Slice("foo4"));
-    ASSERT_OK(s);
-    if (do_prepare) {
-      s = txn0->Prepare();
-      ASSERT_OK(s);
-    }
-    s = txn0->Commit();
-    ASSERT_OK(s);
-    if (!do_prepare) {
-      auto pdb = reinterpret_cast<PessimisticTransactionDB*>(db);
-      pdb->UnregisterTransaction(txn0);
-    }
-    delete txn0;
-    ReadOptions ropt;
-    PinnableSlice pinnable_val;
-
-    s = db->Get(ropt, db->DefaultColumnFamily(), "foo0", &pinnable_val);
-    ASSERT_OK(s);
-    ASSERT_TRUE(pinnable_val == ("bar0b"));
-    s = db->Get(ropt, db->DefaultColumnFamily(), "foo1", &pinnable_val);
-    ASSERT_OK(s);
-    ASSERT_TRUE(pinnable_val == ("bar1"));
-    s = db->Get(ropt, db->DefaultColumnFamily(), "foo2", &pinnable_val);
-    ASSERT_OK(s);
-    ASSERT_TRUE(pinnable_val == ("bar2b"));
-    s = db->Get(ropt, db->DefaultColumnFamily(), "foo3", &pinnable_val);
-    ASSERT_OK(s);
-    ASSERT_TRUE(pinnable_val == ("bar3"));
-    s = db->Get(ropt, db->DefaultColumnFamily(), "foo4", &pinnable_val);
-    ASSERT_TRUE(s.IsNotFound());
+    ASSERT_OK(txn0->Put(Slice("foo0"), Slice("bar0a")));
+    ASSERT_OK(txn0->Put(Slice("foo0"), Slice("bar0b")));
+    txn0->SetSavePoint();
+    txn0->RollbackToSavePoint();
+    ASSERT_OK(txn0->Commit());
   }
 }
 
diff --git a/utilities/transactions/write_prepared_txn.cc b/utilities/transactions/write_prepared_txn.cc
index 7fea5a9df8..01515000d0 100644
--- a/utilities/transactions/write_prepared_txn.cc
+++ b/utilities/transactions/write_prepared_txn.cc
@@ -13,6 +13,7 @@
 
 #include <inttypes.h>
 #include <map>
+#include <set>
 
 #include "db/column_family.h"
 #include "db/db_impl.h"
@@ -30,9 +31,7 @@ WritePreparedTxn::WritePreparedTxn(WritePreparedTxnDB* txn_db,
                                    const WriteOptions& write_options,
                                    const TransactionOptions& txn_options)
     : PessimisticTransaction(txn_db, write_options, txn_options),
-      wpt_db_(txn_db) {
-  GetWriteBatch()->DisableDuplicateMergeKeys();
-}
+      wpt_db_(txn_db) {}
 
 Status WritePreparedTxn::Get(const ReadOptions& read_options,
                              ColumnFamilyHandle* column_family,
@@ -63,6 +62,69 @@ Iterator* WritePreparedTxn::GetIterator(const ReadOptions& options,
   return write_batch_.NewIteratorWithBase(column_family, db_iter);
 }
 
+namespace {
+// A wrapper around Comparator to make it usable in std::set
+struct SetComparator {
+  explicit SetComparator() : user_comparator_(BytewiseComparator()) {}
+  explicit SetComparator(const Comparator* user_comparator)
+      : user_comparator_(user_comparator ? user_comparator
+                                         : BytewiseComparator()) {}
+  bool operator()(const Slice& lhs, const Slice& rhs) const {
+    return user_comparator_->Compare(lhs, rhs) < 0;
+  }
+
+ private:
+  const Comparator* user_comparator_;
+};
+// Count the number of sub-batches inside a batch. A sub-batch does not have
+// duplicate keys.
+struct SubBatchCounter : public WriteBatch::Handler {
+  explicit SubBatchCounter(std::map<uint32_t, const Comparator*>& comparators)
+      : comparators_(comparators), batches_(1) {}
+  std::map<uint32_t, const Comparator*>& comparators_;
+  using CFKeys = std::set<Slice, SetComparator>;
+  std::map<uint32_t, CFKeys> keys_;
+  size_t batches_;
+  size_t BatchCount() { return batches_; }
+  void AddKey(uint32_t cf, const Slice& key) {
+    CFKeys& cf_keys = keys_[cf];
+    if (cf_keys.size() == 0) {  // just inserted
+      auto cmp = comparators_[cf];
+      keys_[cf] = CFKeys(SetComparator(cmp));
+    }
+    auto it = cf_keys.insert(key);
+    if (it.second == false) {  // second is false if a element already existed.
+      batches_++;
+      keys_.clear();
+      keys_[cf].insert(key);
+    }
+  }
+  Status MarkNoop(bool) override { return Status::OK(); }
+  Status MarkEndPrepare(const Slice&) override { return Status::OK(); }
+  Status MarkCommit(const Slice&) override { return Status::OK(); }
+
+  Status PutCF(uint32_t cf, const Slice& key, const Slice&) override {
+    AddKey(cf, key);
+    return Status::OK();
+  }
+  Status DeleteCF(uint32_t cf, const Slice& key) override {
+    AddKey(cf, key);
+    return Status::OK();
+  }
+  Status SingleDeleteCF(uint32_t cf, const Slice& key) override {
+    AddKey(cf, key);
+    return Status::OK();
+  }
+  Status MergeCF(uint32_t cf, const Slice& key, const Slice&) override {
+    AddKey(cf, key);
+    return Status::OK();
+  }
+  Status MarkBeginPrepare() override { return Status::OK(); }
+  Status MarkRollback(const Slice&) override { return Status::OK(); }
+  bool WriteAfterCommit() const override { return false; }
+};
+}  // namespace
+
 Status WritePreparedTxn::PrepareInternal() {
   WriteOptions write_options = write_options_;
   write_options.disableWAL = false;
@@ -71,15 +133,18 @@ Status WritePreparedTxn::PrepareInternal() {
                                      !WRITE_AFTER_COMMIT);
   const bool DISABLE_MEMTABLE = true;
   uint64_t seq_used = kMaxSequenceNumber;
-  bool collapsed = GetWriteBatch()->Collapse();
-  if (collapsed) {
-    ROCKS_LOG_WARN(db_impl_->immutable_db_options().info_log,
-                   "Collapse overhead due to duplicate keys");
+  // For each duplicate key we account for a new sub-batch
+  prepare_batch_cnt_ = 1;
+  if (GetWriteBatch()->HasDuplicateKeys()) {
+    SubBatchCounter counter(*wpt_db_->GetCFComparatorMap());
+    auto s = GetWriteBatch()->GetWriteBatch()->Iterate(&counter);
+    assert(s.ok());
+    prepare_batch_cnt_ = counter.BatchCount();
   }
   Status s =
       db_impl_->WriteImpl(write_options, GetWriteBatch()->GetWriteBatch(),
                           /*callback*/ nullptr, &log_number_, /*log ref*/ 0,
-                          !DISABLE_MEMTABLE, &seq_used);
+                          !DISABLE_MEMTABLE, &seq_used, prepare_batch_cnt_);
   assert(!s.ok() || seq_used != kMaxSequenceNumber);
   auto prepare_seq = seq_used;
   SetId(prepare_seq);
@@ -93,18 +158,32 @@ Status WritePreparedTxn::PrepareInternal() {
 }
 
 Status WritePreparedTxn::CommitWithoutPrepareInternal() {
-  bool collapsed = GetWriteBatch()->Collapse();
-  if (collapsed) {
-    ROCKS_LOG_WARN(db_impl_->immutable_db_options().info_log,
-                   "Collapse overhead due to duplicate keys");
+  // For each duplicate key we account for a new sub-batch
+  size_t batch_cnt = 1;
+  if (GetWriteBatch()->HasDuplicateKeys()) {
+    batch_cnt = 0;  // this will trigger a batch cnt compute
   }
-  return CommitBatchInternal(GetWriteBatch()->GetWriteBatch());
+  return CommitBatchInternal(GetWriteBatch()->GetWriteBatch(), batch_cnt);
 }
 
-Status WritePreparedTxn::CommitBatchInternal(WriteBatch* batch) {
+Status WritePreparedTxn::CommitBatchInternal(WriteBatch* batch,
+                                             size_t batch_cnt) {
   ROCKS_LOG_DETAILS(db_impl_->immutable_db_options().info_log,
                     "CommitBatchInternal");
-  // TODO(myabandeh): handle the duplicate keys in the batch
+  if (batch->Count() == 0) {
+    // Otherwise our 1 seq per batch logic will break since there is no seq
+    // increased for this batch.
+    return Status::OK();
+  }
+  if (batch_cnt == 0) {  // not provided, then compute it
+    // TODO(myabandeh): add an option to allow user skipping this cost
+    SubBatchCounter counter(*wpt_db_->GetCFComparatorMap());
+    auto s = batch->Iterate(&counter);
+    assert(s.ok());
+    batch_cnt = counter.BatchCount();
+  }
+  assert(batch_cnt);
+
   bool do_one_write = !db_impl_->immutable_db_options().two_write_queues;
   bool sync = write_options_.sync;
   if (!do_one_write) {
@@ -116,12 +195,12 @@ Status WritePreparedTxn::CommitBatchInternal(WriteBatch* batch) {
   const bool DISABLE_MEMTABLE = true;
   const uint64_t no_log_ref = 0;
   uint64_t seq_used = kMaxSequenceNumber;
-  const bool INCLUDES_DATA = true;
+  const size_t ZERO_PREPARES = 0;
   WritePreparedCommitEntryPreReleaseCallback update_commit_map(
-      wpt_db_, db_impl_, kMaxSequenceNumber, INCLUDES_DATA);
-  auto s = db_impl_->WriteImpl(write_options_, batch, nullptr, nullptr,
-                               no_log_ref, !DISABLE_MEMTABLE, &seq_used,
-                               do_one_write ? &update_commit_map : nullptr);
+      wpt_db_, db_impl_, kMaxSequenceNumber, ZERO_PREPARES, batch_cnt);
+  auto s = db_impl_->WriteImpl(
+      write_options_, batch, nullptr, nullptr, no_log_ref, !DISABLE_MEMTABLE,
+      &seq_used, batch_cnt, do_one_write ? &update_commit_map : nullptr);
   assert(!s.ok() || seq_used != kMaxSequenceNumber);
   uint64_t& prepare_seq = seq_used;
   SetId(prepare_seq);
@@ -144,13 +223,14 @@ Status WritePreparedTxn::CommitBatchInternal(WriteBatch* batch) {
   // Commit the batch by writing an empty batch to the 2nd queue that will
   // release the commit sequence number to readers.
   WritePreparedCommitEntryPreReleaseCallback update_commit_map_with_prepare(
-      wpt_db_, db_impl_, prepare_seq);
+      wpt_db_, db_impl_, prepare_seq, batch_cnt);
   WriteBatch empty_batch;
   empty_batch.PutLogData(Slice());
+  const size_t ONE_BATCH = 1;
   // In the absence of Prepare markers, use Noop as a batch separator
   WriteBatchInternal::InsertNoop(&empty_batch);
   s = db_impl_->WriteImpl(write_options_, &empty_batch, nullptr, nullptr,
-                          no_log_ref, DISABLE_MEMTABLE, &seq_used,
+                          no_log_ref, DISABLE_MEMTABLE, &seq_used, ONE_BATCH,
                           &update_commit_map_with_prepare);
   assert(!s.ok() || seq_used != kMaxSequenceNumber);
   return s;
@@ -175,17 +255,26 @@ Status WritePreparedTxn::CommitInternal() {
 
   auto prepare_seq = GetId();
   const bool includes_data = !empty && !for_recovery;
+  assert(prepare_batch_cnt_);
+  size_t commit_batch_cnt = 0;
+  if (includes_data) {
+    SubBatchCounter counter(*wpt_db_->GetCFComparatorMap());
+    auto s = working_batch->Iterate(&counter);
+    assert(s.ok());
+    commit_batch_cnt = counter.BatchCount();
+  }
   WritePreparedCommitEntryPreReleaseCallback update_commit_map(
-      wpt_db_, db_impl_, prepare_seq, includes_data);
+      wpt_db_, db_impl_, prepare_seq, prepare_batch_cnt_, commit_batch_cnt);
   const bool disable_memtable = !includes_data;
   uint64_t seq_used = kMaxSequenceNumber;
   // Since the prepared batch is directly written to memtable, there is already
   // a connection between the memtable and its WAL, so there is no need to
   // redundantly reference the log that contains the prepared data.
   const uint64_t zero_log_number = 0ull;
+  size_t batch_cnt = commit_batch_cnt ? commit_batch_cnt : 1;
   auto s = db_impl_->WriteImpl(write_options_, working_batch, nullptr, nullptr,
                                zero_log_number, disable_memtable, &seq_used,
-                               &update_commit_map);
+                               batch_cnt, &update_commit_map);
   assert(!s.ok() || seq_used != kMaxSequenceNumber);
   return s;
 }
@@ -203,16 +292,36 @@ Status WritePreparedTxn::RollbackInternal() {
     ReadOptions roptions;
     WritePreparedTxnReadCallback callback;
     WriteBatch* rollback_batch_;
-    RollbackWriteBatchBuilder(DBImpl* db, WritePreparedTxnDB* wpt_db,
-                              SequenceNumber snap_seq, WriteBatch* dst_batch)
-        : db_(db), callback(wpt_db, snap_seq), rollback_batch_(dst_batch) {}
+    std::map<uint32_t, const Comparator*>& comparators_;
+    using CFKeys = std::set<Slice, SetComparator>;
+    std::map<uint32_t, CFKeys> keys_;
+    RollbackWriteBatchBuilder(
+        DBImpl* db, WritePreparedTxnDB* wpt_db, SequenceNumber snap_seq,
+        WriteBatch* dst_batch,
+        std::map<uint32_t, const Comparator*>& comparators)
+        : db_(db),
+          callback(wpt_db, snap_seq),
+          rollback_batch_(dst_batch),
+          comparators_(comparators) {}
 
     Status Rollback(uint32_t cf, const Slice& key) {
+      Status s;
+      CFKeys& cf_keys = keys_[cf];
+      if (cf_keys.size() == 0) {  // just inserted
+        auto cmp = comparators_[cf];
+        keys_[cf] = CFKeys(SetComparator(cmp));
+      }
+      auto it = cf_keys.insert(key);
+      if (it.second ==
+          false) {  // second is false if a element already existed.
+        return s;
+      }
+
       PinnableSlice pinnable_val;
       bool not_used;
       auto cf_handle = db_->GetColumnFamilyHandle(cf);
-      auto s = db_->GetImpl(roptions, cf_handle, key, &pinnable_val, &not_used,
-                            &callback);
+      s = db_->GetImpl(roptions, cf_handle, key, &pinnable_val, &not_used,
+                       &callback);
       assert(s.ok() || s.IsNotFound());
       if (s.ok()) {
         s = rollback_batch_->Put(cf_handle, key, pinnable_val);
@@ -254,7 +363,8 @@ Status WritePreparedTxn::RollbackInternal() {
 
    protected:
     virtual bool WriteAfterCommit() const override { return false; }
-  } rollback_handler(db_impl_, wpt_db_, last_visible_txn, &rollback_batch);
+  } rollback_handler(db_impl_, wpt_db_, last_visible_txn, &rollback_batch,
+                     *wpt_db_->GetCFComparatorMap());
   auto s = GetWriteBatch()->GetWriteBatch()->Iterate(&rollback_handler);
   assert(s.ok());
   if (!s.ok()) {
@@ -266,11 +376,12 @@ Status WritePreparedTxn::RollbackInternal() {
   const bool DISABLE_MEMTABLE = true;
   const uint64_t no_log_ref = 0;
   uint64_t seq_used = kMaxSequenceNumber;
-  const bool INCLUDES_DATA = true;
+  const size_t ZERO_PREPARES = 0;
+  const size_t ONE_BATCH = 1;
   WritePreparedCommitEntryPreReleaseCallback update_commit_map(
-      wpt_db_, db_impl_, kMaxSequenceNumber, INCLUDES_DATA);
+      wpt_db_, db_impl_, kMaxSequenceNumber, ZERO_PREPARES, ONE_BATCH);
   s = db_impl_->WriteImpl(write_options_, &rollback_batch, nullptr, nullptr,
-                          no_log_ref, !DISABLE_MEMTABLE, &seq_used,
+                          no_log_ref, !DISABLE_MEMTABLE, &seq_used, ONE_BATCH,
                           do_one_write ? &update_commit_map : nullptr);
   assert(!s.ok() || seq_used != kMaxSequenceNumber);
   if (!s.ok()) {
@@ -289,13 +400,13 @@ Status WritePreparedTxn::RollbackInternal() {
   // Commit the batch by writing an empty batch to the queue that will release
   // the commit sequence number to readers.
   WritePreparedCommitEntryPreReleaseCallback update_commit_map_with_prepare(
-      wpt_db_, db_impl_, prepare_seq);
+      wpt_db_, db_impl_, prepare_seq, ONE_BATCH);
   WriteBatch empty_batch;
   empty_batch.PutLogData(Slice());
   // In the absence of Prepare markers, use Noop as a batch separator
   WriteBatchInternal::InsertNoop(&empty_batch);
   s = db_impl_->WriteImpl(write_options_, &empty_batch, nullptr, nullptr,
-                          no_log_ref, DISABLE_MEMTABLE, &seq_used,
+                          no_log_ref, DISABLE_MEMTABLE, &seq_used, ONE_BATCH,
                           &update_commit_map_with_prepare);
   assert(!s.ok() || seq_used != kMaxSequenceNumber);
   // Mark the txn as rolled back
@@ -334,6 +445,18 @@ Status WritePreparedTxn::ValidateSnapshot(ColumnFamilyHandle* column_family,
                                                &snap_checker);
 }
 
+Status WritePreparedTxn::RebuildFromWriteBatch(WriteBatch* src_batch) {
+  auto ret = PessimisticTransaction::RebuildFromWriteBatch(src_batch);
+  prepare_batch_cnt_ = 1;
+  if (GetWriteBatch()->HasDuplicateKeys()) {
+    SubBatchCounter counter(*wpt_db_->GetCFComparatorMap());
+    auto s = GetWriteBatch()->GetWriteBatch()->Iterate(&counter);
+    assert(s.ok());
+    prepare_batch_cnt_ = counter.BatchCount();
+  }
+  return ret;
+}
+
 }  // namespace rocksdb
 
 #endif  // ROCKSDB_LITE
diff --git a/utilities/transactions/write_prepared_txn.h b/utilities/transactions/write_prepared_txn.h
index 17f7d0c96f..de6a72ac9e 100644
--- a/utilities/transactions/write_prepared_txn.h
+++ b/utilities/transactions/write_prepared_txn.h
@@ -68,7 +68,7 @@ class WritePreparedTxn : public PessimisticTransaction {
 
   Status CommitWithoutPrepareInternal() override;
 
-  Status CommitBatchInternal(WriteBatch* batch) override;
+  Status CommitBatchInternal(WriteBatch* batch, size_t batch_cnt) override;
 
   // Since the data is already written to memtables at the Prepare phase, the
   // commit entails writing only a commit marker in the WAL. The sequence number
@@ -84,11 +84,15 @@ class WritePreparedTxn : public PessimisticTransaction {
                                   const Slice& key,
                                   SequenceNumber* tracked_at_seq) override;
 
+  virtual Status RebuildFromWriteBatch(WriteBatch* src_batch) override;
+
   // No copying allowed
   WritePreparedTxn(const WritePreparedTxn&);
   void operator=(const WritePreparedTxn&);
 
   WritePreparedTxnDB* wpt_db_;
+  // Number of sub-batches in prepare
+  size_t prepare_batch_cnt_ = 0;
 };
 
 }  // namespace rocksdb
diff --git a/utilities/transactions/write_prepared_txn_db.cc b/utilities/transactions/write_prepared_txn_db.cc
index 867b757da5..79a3b727b7 100644
--- a/utilities/transactions/write_prepared_txn_db.cc
+++ b/utilities/transactions/write_prepared_txn_db.cc
@@ -11,7 +11,6 @@
 
 #include "utilities/transactions/write_prepared_txn_db.h"
 
-#include <inttypes.h>
 #include <algorithm>
 #include <string>
 #include <unordered_set>
@@ -49,6 +48,20 @@ Status WritePreparedTxnDB::Initialize(
   return s;
 }
 
+Status WritePreparedTxnDB::VerifyCFOptions(
+    const ColumnFamilyOptions& cf_options) {
+  Status s = PessimisticTransactionDB::VerifyCFOptions(cf_options);
+  if (!s.ok()) {
+    return s;
+  }
+  if (!cf_options.memtable_factory->CanHandleDuplicatedKey()) {
+    return Status::InvalidArgument(
+        "memtable_factory->CanHandleDuplicatedKey() cannot be false with "
+        "WritePrpeared transactions");
+  }
+  return Status::OK();
+}
+
 Transaction* WritePreparedTxnDB::BeginTransaction(
     const WriteOptions& write_options, const TransactionOptions& txn_options,
     Transaction* old_txn) {
diff --git a/utilities/transactions/write_prepared_txn_db.h b/utilities/transactions/write_prepared_txn_db.h
index 4e83609fed..0b096e4c23 100644
--- a/utilities/transactions/write_prepared_txn_db.h
+++ b/utilities/transactions/write_prepared_txn_db.h
@@ -205,6 +205,10 @@ class WritePreparedTxnDB : public PessimisticTransactionDB {
   // Struct to hold ownership of snapshot and read callback for cleanup.
   struct IteratorState;
 
+ protected:
+  virtual Status VerifyCFOptions(
+      const ColumnFamilyOptions& cf_options) override;
+
  private:
   friend class WritePreparedTransactionTest_IsInSnapshotTest_Test;
   friend class WritePreparedTransactionTest_CheckAgainstSnapshotsTest_Test;
@@ -401,30 +405,48 @@ class WritePreparedCommitEntryPreReleaseCallback : public PreReleaseCallback {
  public:
   // includes_data indicates that the commit also writes non-empty
   // CommitTimeWriteBatch to memtable, which needs to be committed separately.
-  WritePreparedCommitEntryPreReleaseCallback(
-      WritePreparedTxnDB* db, DBImpl* db_impl,
-      SequenceNumber prep_seq = kMaxSequenceNumber, bool includes_data = false)
+  WritePreparedCommitEntryPreReleaseCallback(WritePreparedTxnDB* db,
+                                             DBImpl* db_impl,
+                                             SequenceNumber prep_seq,
+                                             size_t prep_batch_cnt,
+                                             size_t data_batch_cnt = 0)
       : db_(db),
         db_impl_(db_impl),
         prep_seq_(prep_seq),
-        includes_data_(includes_data) {}
+        prep_batch_cnt_(prep_batch_cnt),
+        data_batch_cnt_(data_batch_cnt),
+        includes_data_(data_batch_cnt_ > 0) {
+    assert((prep_batch_cnt_ > 0) != (prep_seq == kMaxSequenceNumber));  // xor
+    assert(prep_batch_cnt_ > 0 || data_batch_cnt_ > 0);
+  }
 
-  virtual Status Callback(SequenceNumber commit_seq) {
+  virtual Status Callback(SequenceNumber commit_seq) override {
     assert(includes_data_ || prep_seq_ != kMaxSequenceNumber);
+    const uint64_t last_commit_seq = LIKELY(data_batch_cnt_ <= 1)
+                                         ? commit_seq
+                                         : commit_seq + data_batch_cnt_ - 1;
     if (prep_seq_ != kMaxSequenceNumber) {
-      db_->AddCommitted(prep_seq_, commit_seq);
+      for (size_t i = 0; i < prep_batch_cnt_; i++) {
+        db_->AddCommitted(prep_seq_ + i, last_commit_seq);
+      }
     }  // else there was no prepare phase
     if (includes_data_) {
+      assert(data_batch_cnt_);
       // Commit the data that is accompnaied with the commit request
       const bool PREPARE_SKIPPED = true;
-      db_->AddCommitted(commit_seq, commit_seq, PREPARE_SKIPPED);
+      for (size_t i = 0; i < data_batch_cnt_; i++) {
+        // For commit seq of each batch use the commit seq of the last batch.
+        // This would make debugging easier by having all the batches having
+        // the same sequence number.
+        db_->AddCommitted(commit_seq + i, last_commit_seq, PREPARE_SKIPPED);
+      }
     }
     if (db_impl_->immutable_db_options().two_write_queues) {
       // Publish the sequence number. We can do that here assuming the callback
       // is invoked only from one write queue, which would guarantee that the
       // publish sequence numbers will be in order, i.e., once a seq is
       // published all the seq prior to that are also publishable.
-      db_impl_->SetLastPublishedSequence(commit_seq);
+      db_impl_->SetLastPublishedSequence(last_commit_seq);
     }
     // else SequenceNumber that is updated as part of the write already does the
     // publishing
@@ -436,6 +458,8 @@ class WritePreparedCommitEntryPreReleaseCallback : public PreReleaseCallback {
   DBImpl* db_impl_;
   // kMaxSequenceNumber if there was no prepare phase
   SequenceNumber prep_seq_;
+  size_t prep_batch_cnt_;
+  size_t data_batch_cnt_;
   // Either because it is commit without prepare or it has a
   // CommitTimeWriteBatch
   bool includes_data_;
diff --git a/utilities/write_batch_with_index/write_batch_with_index.cc b/utilities/write_batch_with_index/write_batch_with_index.cc
index 6e36c430f0..6f26c13286 100644
--- a/utilities/write_batch_with_index/write_batch_with_index.cc
+++ b/utilities/write_batch_with_index/write_batch_with_index.cc
@@ -582,67 +582,8 @@ void WriteBatchWithIndex::Rep::AddNewEntry(uint32_t column_family_id) {
 
   WriteBatch* WriteBatchWithIndex::GetWriteBatch() { return &rep->write_batch; }
 
-  bool WriteBatchWithIndex::Collapse() {
-    if (rep->obsolete_offsets.size() == 0) {
-      return false;
-    }
-    std::sort(rep->obsolete_offsets.begin(), rep->obsolete_offsets.end());
-    WriteBatch& write_batch = rep->write_batch;
-    assert(write_batch.Count() != 0);
-    size_t offset = WriteBatchInternal::GetFirstOffset(&write_batch);
-    Slice input(write_batch.Data());
-    input.remove_prefix(offset);
-    std::string collapsed_buf;
-    collapsed_buf.resize(WriteBatchInternal::kHeader);
-
-    size_t count = 0;
-    Status s;
-    // Loop through all entries in the write batch and add keep them if they are
-    // not obsolete by a newere entry.
-    while (s.ok() && !input.empty()) {
-      Slice key, value, blob, xid;
-      uint32_t column_family_id = 0;  // default
-      char tag = 0;
-      // set offset of current entry for call to AddNewEntry()
-      size_t last_entry_offset = input.data() - write_batch.Data().data();
-      s = ReadRecordFromWriteBatch(&input, &tag, &column_family_id, &key,
-                                   &value, &blob, &xid);
-      if (!rep->obsolete_offsets.empty() && 
-        rep->obsolete_offsets.front() == last_entry_offset) {
-        rep->obsolete_offsets.erase(rep->obsolete_offsets.begin());
-        continue;
-      }
-      switch (tag) {
-        case kTypeColumnFamilyValue:
-        case kTypeValue:
-        case kTypeColumnFamilyDeletion:
-        case kTypeDeletion:
-        case kTypeColumnFamilySingleDeletion:
-        case kTypeSingleDeletion:
-        case kTypeColumnFamilyMerge:
-        case kTypeMerge:
-          count++;
-          break;
-        case kTypeLogData:
-        case kTypeBeginPrepareXID:
-        case kTypeBeginPersistedPrepareXID:
-        case kTypeEndPrepareXID:
-        case kTypeCommitXID:
-        case kTypeRollbackXID:
-        case kTypeNoop:
-          break;
-        default:
-          assert(0);
-      }
-      size_t entry_offset = input.data() - write_batch.Data().data();
-      const std::string& wb_data = write_batch.Data();
-      Slice entry_ptr = Slice(wb_data.data() + last_entry_offset,
-                              entry_offset - last_entry_offset);
-      collapsed_buf.append(entry_ptr.data(), entry_ptr.size());
-    }
-    write_batch.rep_ = std::move(collapsed_buf);
-    WriteBatchInternal::SetCount(&write_batch, static_cast<int>(count));
-    return true;
+  bool WriteBatchWithIndex::HasDuplicateKeys() {
+    return rep->obsolete_offsets.size() > 0;
   }
 
   WBWIIterator* WriteBatchWithIndex::NewIterator() {
@@ -758,15 +699,7 @@ Status WriteBatchWithIndex::Merge(ColumnFamilyHandle* column_family,
   rep->SetLastEntryOffset();
   auto s = rep->write_batch.Merge(column_family, key, value);
   if (s.ok()) {
-    auto size_before = rep->obsolete_offsets.size();
     rep->AddOrUpdateIndex(column_family, key);
-    auto size_after = rep->obsolete_offsets.size();
-    bool duplicate_key = size_before != size_after;
-    if (!allow_dup_merge_ && duplicate_key) {
-      assert(0);
-      return Status::NotSupported(
-          "Duplicate key with merge value is not supported yet");
-    }
   }
   return s;
 }
@@ -775,15 +708,7 @@ Status WriteBatchWithIndex::Merge(const Slice& key, const Slice& value) {
   rep->SetLastEntryOffset();
   auto s = rep->write_batch.Merge(key, value);
   if (s.ok()) {
-    auto size_before = rep->obsolete_offsets.size();
     rep->AddOrUpdateIndex(key);
-    auto size_after = rep->obsolete_offsets.size();
-    bool duplicate_key = size_before != size_after;
-    if (!allow_dup_merge_ && duplicate_key) {
-      assert(0);
-      return Status::NotSupported(
-          "Duplicate key with merge value is not supported yet");
-    }
   }
   return s;
 }
@@ -958,8 +883,9 @@ Status WriteBatchWithIndex::RollbackToSavePoint() {
   Status s = rep->write_batch.RollbackToSavePoint();
 
   if (s.ok()) {
-    s = rep->ReBuildIndex();
+    // obsolete_offsets will be rebuilt by ReBuildIndex
     rep->obsolete_offsets.clear();
+    s = rep->ReBuildIndex();
   }
 
   return s;