diff --git a/src/facade/op_status.h b/src/facade/op_status.h
index bad993a..434ce24 100644
--- a/src/facade/op_status.h
+++ b/src/facade/op_status.h
@@ -19,6 +19,8 @@ enum class OpStatus : uint16_t {
   TIMED_OUT,
   OUT_OF_MEMORY,
   INVALID_FLOAT,
+  INVALID_INT,
+  SYNTAX_ERR,
 };
 
 class OpResultBase {
diff --git a/src/facade/reply_builder.cc b/src/facade/reply_builder.cc
index 31cd810..822aa1c 100644
--- a/src/facade/reply_builder.cc
+++ b/src/facade/reply_builder.cc
@@ -153,7 +153,6 @@ void MCReplyBuilder::SendNotFound() {
   SendSimpleString("NOT_FOUND");
 }
 
-
 char* RedisReplyBuilder::FormatDouble(double val, char* dest, unsigned dest_len) {
   StringBuilder sb(dest, dest_len);
   CHECK(dfly_conv.ToShortest(val, &sb));
@@ -229,6 +228,12 @@ void RedisReplyBuilder::SendError(OpStatus status) {
     case OpStatus::INVALID_FLOAT:
       SendError(kInvalidFloatErr);
       break;
+    case OpStatus::INVALID_INT:
+      SendError(kInvalidIntErr);
+      break;
+    case OpStatus::SYNTAX_ERR:
+      SendError(kSyntaxErr);
+      break;
     default:
       LOG(ERROR) << "Unsupported status " << status;
       SendError("Internal error");
diff --git a/src/server/command_registry.cc b/src/server/command_registry.cc
index 4b785b7..ece7e7d 100644
--- a/src/server/command_registry.cc
+++ b/src/server/command_registry.cc
@@ -21,9 +21,11 @@ CommandId::CommandId(const char* name, uint32_t mask, int8_t arity, int8_t first
                      int8_t last_key, int8_t step)
     : name_(name), opt_mask_(mask), arity_(arity), first_key_(first_key), last_key_(last_key),
       step_key_(step) {
-  if (mask & CO::ADMIN) {
+  if (mask & CO::ADMIN)
     opt_mask_ |= CO::NOSCRIPT;
-  }
+
+  if (mask & CO::BLOCKING)
+    opt_mask_ |= CO::REVERSE_MAPPING;
 }
 
 uint32_t CommandId::OptCount(uint32_t mask) {
@@ -81,38 +83,6 @@ CommandRegistry& CommandRegistry::operator<<(CommandId cmd) {
   return *this;
 }
 
-KeyIndex DetermineKeys(const CommandId* cid, const CmdArgList& args) {
-  DCHECK_EQ(0u, cid->opt_mask() & CO::GLOBAL_TRANS);
-
-  KeyIndex key_index;
-
-  if (cid->first_key_pos() > 0) {
-    key_index.start = cid->first_key_pos();
-    int last = cid->last_key_pos();
-    key_index.end = last > 0 ? last + 1 : (int(args.size()) + 1 + last);
-    key_index.step = cid->key_arg_step();
-
-    return key_index;
-  }
-
-  string_view name{cid->name()};
-  if (name == "EVAL" || name == "EVALSHA") {
-    DCHECK_GE(args.size(), 3u);
-    uint32_t num_keys;
-
-    CHECK(absl::SimpleAtoi(ArgS(args, 2), &num_keys));
-    key_index.start = 3;
-    key_index.end = 3 + num_keys;
-    key_index.step = 1;
-
-    return key_index;
-  }
-
-  LOG(FATAL) << "TBD: Not supported";
-
-  return key_index;
-}
-
 namespace CO {
 
 const char* OptName(CO::CommandOpt fl) {
@@ -125,6 +95,8 @@ const char* OptName(CO::CommandOpt fl) {
       return "readonly";
     case DENYOOM:
       return "denyoom";
+    case REVERSE_MAPPING:
+      return "reverse-mapping";
     case FAST:
       return "fast";
     case LOADING:
@@ -139,6 +111,8 @@ const char* OptName(CO::CommandOpt fl) {
       return "blocking";
     case GLOBAL_TRANS:
       return "global-trans";
+    case DESTINATION_KEY:
+      return "dest-key";
   }
   return "unknown";
 }
diff --git a/src/server/command_registry.h b/src/server/command_registry.h
index 589a567..1bd6a15 100644
--- a/src/server/command_registry.h
+++ b/src/server/command_registry.h
@@ -24,11 +24,13 @@ enum CommandOpt : uint32_t {
   WRITE = 4,
   LOADING = 8,
   DENYOOM = 0x10,  // use-memory in redis.
+  REVERSE_MAPPING = 0x20,
   RANDOM = 0x40,
   ADMIN = 0x80,  // implies NOSCRIPT,
   NOSCRIPT = 0x100,
-  BLOCKING = 0x200,
+  BLOCKING = 0x200,  // implies REVERSE_MAPPING
   GLOBAL_TRANS = 0x1000,
+  DESTINATION_KEY = 0x2000,
 };
 
 const char* OptName(CommandOpt fl);
@@ -83,7 +85,7 @@ class CommandId {
   }
 
   bool is_multi_key() const {
-    return last_key_ != first_key_;
+    return (last_key_ != first_key_) || (opt_mask_ & CO::DESTINATION_KEY);
   }
 
   int8_t key_arg_step() const {
@@ -157,8 +159,4 @@ class CommandRegistry {
   void Command(CmdArgList args, ConnectionContext* cntx);
 };
 
-
-// Given the command and the arguments determines the keys range (index).
-KeyIndex DetermineKeys(const CommandId* cid, const CmdArgList& args);
-
 }  // namespace dfly
diff --git a/src/server/common.h b/src/server/common.h
index 0d3f3a5..f7777b4 100644
--- a/src/server/common.h
+++ b/src/server/common.h
@@ -48,9 +48,20 @@ struct KeyLockArgs {
 
 // Describes key indices.
 struct KeyIndex {
+  // if index is non-zero then adds another key index (usually 1).
+  // relevant for for commands like ZUNIONSTORE/ZINTERSTORE for destination key.
+  unsigned bonus = 0;
   unsigned start;
   unsigned end;  // does not include this index (open limit).
   unsigned step; // 1 for commands like mget. 2 for commands like mset.
+
+  bool HasSingleKey() const {
+    return bonus == 0 && (start + step >= end);
+  }
+
+  unsigned num_args() const {
+    return end - start + (bonus > 0);
+  }
 };
 
 struct OpArgs {
diff --git a/src/server/main_service.cc b/src/server/main_service.cc
index c165ebe..6a1c126 100644
--- a/src/server/main_service.cc
+++ b/src/server/main_service.cc
@@ -354,6 +354,12 @@ void Service::Shutdown() {
   boost::this_fiber::sleep_for(10ms);
 }
 
+static void MultiSetError(ConnectionContext* cntx) {
+  if (cntx->conn_state.exec_state != ConnectionState::EXEC_INACTIVE) {
+    cntx->conn_state.exec_state = ConnectionState::EXEC_ERROR;
+  }
+}
+
 void Service::DispatchCommand(CmdArgList args, facade::ConnectionContext* cntx) {
   CHECK(!args.empty());
   DCHECK_NE(0u, shard_set_.size()) << "Init was not called";
@@ -370,11 +376,7 @@ void Service::DispatchCommand(CmdArgList args, facade::ConnectionContext* cntx)
   etl.RecordCmd();
 
   ConnectionContext* dfly_cntx = static_cast<ConnectionContext*>(cntx);
-  absl::Cleanup multi_error = [dfly_cntx] {
-    if (dfly_cntx->conn_state.exec_state != ConnectionState::EXEC_INACTIVE) {
-      dfly_cntx->conn_state.exec_state = ConnectionState::EXEC_ERROR;
-    }
-  };
+  absl::Cleanup multi_error([dfly_cntx] { MultiSetError(dfly_cntx); });
 
   if (cid == nullptr) {
     (*cntx)->SendError(absl::StrCat("unknown command `", cmd_str, "`"), "unknown_cmd");
@@ -464,7 +466,11 @@ void Service::DispatchCommand(CmdArgList args, facade::ConnectionContext* cntx)
 
   if (under_script) {
     DCHECK(dfly_cntx->transaction);
-    KeyIndex key_index = DetermineKeys(cid, args);
+    OpResult<KeyIndex> key_index_res = DetermineKeys(cid, args);
+    if (!key_index_res)
+      return (*cntx)->SendError(key_index_res.status());
+
+    const auto& key_index = *key_index_res;
     for (unsigned i = key_index.start; i < key_index.end; ++i) {
       string_view key = ArgS(args, i);
       if (!dfly_cntx->conn_state.script_info->keys.contains(key)) {
@@ -472,7 +478,9 @@ void Service::DispatchCommand(CmdArgList args, facade::ConnectionContext* cntx)
       }
     }
     dfly_cntx->transaction->SetExecCmd(cid);
-    dfly_cntx->transaction->InitByArgs(dfly_cntx->conn_state.db_index, args);
+    OpStatus st = dfly_cntx->transaction->InitByArgs(dfly_cntx->conn_state.db_index, args);
+    if (st != OpStatus::OK)
+      return (*cntx)->SendError(st);
   } else {
     DCHECK(dfly_cntx->transaction == nullptr);
 
@@ -480,7 +488,10 @@ void Service::DispatchCommand(CmdArgList args, facade::ConnectionContext* cntx)
       dist_trans.reset(new Transaction{cid, &shard_set_});
       dfly_cntx->transaction = dist_trans.get();
 
-      dist_trans->InitByArgs(dfly_cntx->conn_state.db_index, args);
+      OpStatus st = dist_trans->InitByArgs(dfly_cntx->conn_state.db_index, args);
+      if (st != OpStatus::OK)
+        return (*cntx)->SendError(st);
+
       dfly_cntx->last_command_debug.shards_count = dfly_cntx->transaction->unique_shard_cnt();
     } else {
       dfly_cntx->transaction = nullptr;
@@ -856,7 +867,11 @@ void Service::Exec(CmdArgList args, ConnectionContext* cntx) {
       cntx->transaction->SetExecCmd(scmd.descr);
       CmdArgList cmd_arg_list{str_list.data(), str_list.size()};
       if (IsTransactional(scmd.descr)) {
-        cntx->transaction->InitByArgs(cntx->conn_state.db_index, cmd_arg_list);
+        OpStatus st = cntx->transaction->InitByArgs(cntx->conn_state.db_index, cmd_arg_list);
+        if (st != OpStatus::OK) {
+          (*cntx)->SendError(st);
+          break;
+        }
       }
       scmd.descr->Invoke(cmd_arg_list, cntx);
       if (rb->GetError())
diff --git a/src/server/server_family.cc b/src/server/server_family.cc
index 7accd33..7b0a284 100644
--- a/src/server/server_family.cc
+++ b/src/server/server_family.cc
@@ -332,6 +332,18 @@ void ServerFamily::Auth(CmdArgList args, ConnectionContext* cntx) {
   }
 }
 
+void ServerFamily::Client(CmdArgList args, ConnectionContext* cntx) {
+  ToUpper(&args[1]);
+  string_view sub_cmd = ArgS(args, 1);
+
+  if (sub_cmd == "SETNAME") {
+    return (*cntx)->SendOk();
+  }
+
+  LOG_FIRST_N(ERROR, 10) << "Subcommand " << sub_cmd << " not supported";
+  (*cntx)->SendError(kSyntaxErr);
+}
+
 void ServerFamily::Config(CmdArgList args, ConnectionContext* cntx) {
   ToUpper(&args[1]);
   string_view sub_cmd = ArgS(args, 1);
@@ -678,6 +690,18 @@ void ServerFamily::LastSave(CmdArgList args, ConnectionContext* cntx) {
   (*cntx)->SendLong(last_save_);
 }
 
+void ServerFamily::Latency(CmdArgList args, ConnectionContext* cntx) {
+  ToUpper(&args[1]);
+  string_view sub_cmd = ArgS(args, 1);
+
+  if (sub_cmd == "LATEST") {
+    return (*cntx)->StartArray(0);
+  }
+
+  LOG_FIRST_N(ERROR, 10) << "Subcommand " << sub_cmd << " not supported";
+  (*cntx)->SendError(kSyntaxErr);
+}
+
 void ServerFamily::_Shutdown(CmdArgList args, ConnectionContext* cntx) {
   CHECK_NOTNULL(acceptor_)->Stop();
   (*cntx)->SendOk();
@@ -705,6 +729,7 @@ void ServerFamily::Register(CommandRegistry* registry) {
 
   *registry << CI{"AUTH", CO::NOSCRIPT | CO::FAST | CO::LOADING, -2, 0, 0, 0}.HFUNC(Auth)
             << CI{"BGSAVE", CO::ADMIN | CO::GLOBAL_TRANS, 1, 0, 0, 0}.HFUNC(Save)
+            << CI{"CLIENT", CO::NOSCRIPT | CO::LOADING, -2, 0, 0, 0}.HFUNC(Client)
             << CI{"CONFIG", CO::ADMIN, -2, 0, 0, 0}.HFUNC(Config)
             << CI{"DBSIZE", CO::READONLY | CO::FAST | CO::LOADING, 1, 0, 0, 0}.HFUNC(DbSize)
             << CI{"DEBUG", CO::RANDOM | CO::ADMIN | CO::LOADING, -2, 0, 0, 0}.HFUNC(Debug)
@@ -713,6 +738,8 @@ void ServerFamily::Register(CommandRegistry* registry) {
             << CI{"INFO", CO::LOADING, -1, 0, 0, 0}.HFUNC(Info)
             << CI{"HELLO", CO::LOADING, -1, 0, 0, 0}.HFUNC(Hello)
             << CI{"LASTSAVE", CO::LOADING | CO::RANDOM | CO::FAST, 1, 0, 0, 0}.HFUNC(LastSave)
+            << CI{"LATENCY", CO::NOSCRIPT | CO::LOADING | CO::RANDOM | CO::FAST, -2, 0, 0, 0}.HFUNC(
+                   Latency)
             << CI{"MEMORY", kMemOpts, -2, 0, 0, 0}.HFUNC(Memory)
             << CI{"SAVE", CO::ADMIN | CO::GLOBAL_TRANS, 1, 0, 0, 0}.HFUNC(Save)
             << CI{"SHUTDOWN", CO::ADMIN | CO::NOSCRIPT | CO::LOADING, 1, 0, 0, 0}.HFUNC(_Shutdown)
diff --git a/src/server/server_family.h b/src/server/server_family.h
index 30df823..8b477d0 100644
--- a/src/server/server_family.h
+++ b/src/server/server_family.h
@@ -68,6 +68,7 @@ class ServerFamily {
   }
 
   void Auth(CmdArgList args, ConnectionContext* cntx);
+  void Client(CmdArgList args, ConnectionContext* cntx);
   void Config(CmdArgList args, ConnectionContext* cntx);
   void DbSize(CmdArgList args, ConnectionContext* cntx);
   void Debug(CmdArgList args, ConnectionContext* cntx);
@@ -77,6 +78,7 @@ class ServerFamily {
   void Info(CmdArgList args, ConnectionContext* cntx);
   void Hello(CmdArgList args, ConnectionContext* cntx);
   void LastSave(CmdArgList args, ConnectionContext* cntx);
+  void Latency(CmdArgList args, ConnectionContext* cntx);
   void Psync(CmdArgList args, ConnectionContext* cntx);
   void ReplicaOf(CmdArgList args, ConnectionContext* cntx);
   void Role(CmdArgList args, ConnectionContext* cntx);
@@ -84,6 +86,7 @@ class ServerFamily {
   void Script(CmdArgList args, ConnectionContext* cntx);
   void Sync(CmdArgList args, ConnectionContext* cntx);
 
+
   void _Shutdown(CmdArgList args, ConnectionContext* cntx);
 
   void SyncGeneric(std::string_view repl_master_id, uint64_t offs, ConnectionContext* cntx);
diff --git a/src/server/string_family.cc b/src/server/string_family.cc
index e9c5be2..8cd6022 100644
--- a/src/server/string_family.cc
+++ b/src/server/string_family.cc
@@ -904,7 +904,7 @@ void StringFamily::Register(CommandRegistry* registry) {
             << CI{"DECRBY", CO::WRITE | CO::DENYOOM | CO::FAST, 3, 1, 1, 1}.HFUNC(DecrBy)
             << CI{"GET", CO::READONLY | CO::FAST, 2, 1, 1, 1}.HFUNC(Get)
             << CI{"GETSET", CO::WRITE | CO::DENYOOM | CO::FAST, 3, 1, 1, 1}.HFUNC(GetSet)
-            << CI{"MGET", CO::READONLY | CO::FAST, -2, 1, -1, 1}.HFUNC(MGet)
+            << CI{"MGET", CO::READONLY | CO::FAST | CO::REVERSE_MAPPING, -2, 1, -1, 1}.HFUNC(MGet)
             << CI{"MSET", CO::WRITE | CO::DENYOOM, -3, 1, -1, 2}.HFUNC(MSet)
             << CI{"MSETNX", CO::WRITE | CO::DENYOOM, -3, 1, -1, 2}.HFUNC(MSetNx)
             << CI{"STRLEN", CO::READONLY | CO::FAST, 2, 1, 1, 1}.HFUNC(StrLen)
diff --git a/src/server/transaction.cc b/src/server/transaction.cc
index c8b1256..fa53c89 100644
--- a/src/server/transaction.cc
+++ b/src/server/transaction.cc
@@ -74,36 +74,42 @@ Transaction::~Transaction() {
  *
  **/
 
-void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
+OpStatus Transaction::InitByArgs(DbIndex index, CmdArgList args) {
   db_index_ = index;
 
   if (IsGlobal()) {
     unique_shard_cnt_ = ess_->size();
     shard_data_.resize(unique_shard_cnt_);
-    return;
+    return OpStatus::OK;
   }
 
   CHECK_GT(args.size(), 1U);  // first entry is the command name.
   DCHECK_EQ(unique_shard_cnt_, 0u);
   DCHECK(args_.empty());
 
-  KeyIndex key_index = DetermineKeys(cid_, args);
+  OpResult<KeyIndex> key_index_res = DetermineKeys(cid_, args);
+  if (!key_index_res)
+    return key_index_res.status();
+
+  const auto& key_index = *key_index_res;
 
   if (key_index.start == args.size()) {  // eval with 0 keys.
     CHECK(absl::StartsWith(cid_->name(), "EVAL"));
-    return;
+    return OpStatus::OK;
   }
 
   DCHECK_LT(key_index.start, args.size());
   DCHECK_GT(key_index.start, 0u);
 
   bool incremental_locking = multi_ && multi_->incremental;
-  bool single_key = !multi_ && (key_index.start + key_index.step) >= key_index.end;
+  bool single_key = !multi_ && key_index.HasSingleKey();
 
   if (single_key) {
     DCHECK_GT(key_index.step, 0u);
 
     shard_data_.resize(1);  // Single key optimization
+
+    // even for a single key we may have multiple arguments per key (MSET).
     for (unsigned j = key_index.start; j < key_index.start + key_index.step; ++j) {
       args_.push_back(ArgS(args, j));
     }
@@ -112,7 +118,7 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
     unique_shard_cnt_ = 1;
     unique_shard_id_ = Shard(key, ess_->size());
 
-    return;
+    return OpStatus::OK;
   }
 
   // Our shard_data is not sparse, so we must allocate for all threads :(
@@ -131,6 +137,8 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
   // and regular commands.
   IntentLock::Mode mode = IntentLock::EXCLUSIVE;
   bool should_record_locks = false;
+  bool needs_reverse_mapping = cid_->opt_mask() & CO::REVERSE_MAPPING;
+
   if (multi_) {
     mode = Mode();
     tmp_space.uniq_keys.clear();
@@ -138,11 +146,22 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
     should_record_locks = incremental_locking || !multi_->locks_recorded;
   }
 
+  if (key_index.bonus) {  // additional one-of key.
+    DCHECK(key_index.step == 1);
+    DCHECK(!needs_reverse_mapping);
+
+    string_view key = ArgS(args, key_index.bonus);
+    uint32_t sid = Shard(key, shard_data_.size());
+    shard_index[sid].args.push_back(key);
+  }
+
   for (unsigned i = key_index.start; i < key_index.end; ++i) {
     string_view key = ArgS(args, i);
     uint32_t sid = Shard(key, shard_data_.size());
+
     shard_index[sid].args.push_back(key);
-    shard_index[sid].original_index.push_back(i - 1);
+    if (needs_reverse_mapping)
+      shard_index[sid].original_index.push_back(i - 1);
 
     if (should_record_locks && tmp_space.uniq_keys.insert(key).second) {
       multi_->locks[key].cnt[int(mode)]++;
@@ -150,9 +169,11 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
 
     if (key_index.step == 2) {  // value
       ++i;
-      auto val = ArgS(args, i);
+
+      string_view val = ArgS(args, i);
       shard_index[sid].args.push_back(val);
-      shard_index[sid].original_index.push_back(i - 1);
+      if (needs_reverse_mapping)
+        shard_index[sid].original_index.push_back(i - 1);
     }
   }
 
@@ -160,8 +181,11 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
     multi_->locks_recorded = true;
   }
 
-  args_.resize(key_index.end - key_index.start);
-  reverse_index_.resize(args_.size());
+  args_.resize(key_index.num_args());
+
+  // we need reverse index only for blocking commands or commands like MSET.
+  if (needs_reverse_mapping)
+    reverse_index_.resize(args_.size());
 
   auto next_arg = args_.begin();
   auto rev_indx_it = reverse_index_.begin();
@@ -192,11 +216,11 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
     uint32_t orig_indx = 0;
     for (size_t j = 0; j < si.args.size(); ++j) {
       *next_arg = si.args[j];
-      *rev_indx_it = si.original_index[orig_indx];
-
+      if (needs_reverse_mapping) {
+        *rev_indx_it++ = si.original_index[orig_indx];
+      }
       ++next_arg;
       ++orig_indx;
-      ++rev_indx_it;
     }
   }
 
@@ -224,6 +248,8 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
       DCHECK_EQ(TxQueue::kEnd, sd.pq_pos);
     }
   }
+
+  return OpStatus::OK;
 }
 
 void Transaction::SetExecCmd(const CommandId* cid) {
@@ -1126,4 +1152,53 @@ void Transaction::BreakOnClose() {
   }
 }
 
+
+OpResult<KeyIndex> DetermineKeys(const CommandId* cid, CmdArgList args) {
+  DCHECK_EQ(0u, cid->opt_mask() & CO::GLOBAL_TRANS);
+
+  KeyIndex key_index;
+  int num_custom_keys = -1;
+
+  if (cid->opt_mask() & CO::DESTINATION_KEY) {
+    key_index.bonus = 1;
+    if (args.size() < 3) {
+      return OpStatus::SYNTAX_ERR;
+    }
+    string_view num(ArgS(args, 2));
+    if (!absl::SimpleAtoi(num, &num_custom_keys) || num_custom_keys < 0 ||
+        size_t(num_custom_keys) + 3 > args.size())
+      return OpStatus::INVALID_INT;
+  }
+
+  if (cid->first_key_pos() > 0) {
+    key_index.start = cid->first_key_pos();
+    int last = cid->last_key_pos();
+    if (num_custom_keys >= 0) {
+      key_index.end = key_index.start + num_custom_keys;
+    } else {
+      key_index.end = last > 0 ? last + 1 : (int(args.size()) + 1 + last);
+    }
+    key_index.step = cid->key_arg_step();
+
+    return key_index;
+  }
+
+  string_view name{cid->name()};
+  if (name == "EVAL" || name == "EVALSHA") {
+    DCHECK_GE(args.size(), 3u);
+    uint32_t num_keys;
+
+    CHECK(absl::SimpleAtoi(ArgS(args, 2), &num_keys));
+    key_index.start = 3;
+    key_index.end = 3 + num_keys;
+    key_index.step = 1;
+
+    return key_index;
+  }
+
+  LOG(FATAL) << "TBD: Not supported";
+
+  return key_index;
+}
+
 }  // namespace dfly
diff --git a/src/server/transaction.h b/src/server/transaction.h
index 0cc9956..bc0331c 100644
--- a/src/server/transaction.h
+++ b/src/server/transaction.h
@@ -61,7 +61,7 @@ class Transaction {
 
   Transaction(const CommandId* cid, EngineShardSet* ess);
 
-  void InitByArgs(DbIndex index, CmdArgList args);
+  OpStatus InitByArgs(DbIndex index, CmdArgList args);
 
   void SetExecCmd(const CommandId* cid);
 
@@ -342,4 +342,6 @@ inline uint16_t trans_id(const Transaction* ptr) {
   return intptr_t(ptr) & 0xFFFF;
 }
 
+OpResult<KeyIndex> DetermineKeys(const CommandId* cid, CmdArgList args);
+
 }  // namespace dfly
diff --git a/src/server/zset_family.cc b/src/server/zset_family.cc
index 3632499..aa2ac87 100644
--- a/src/server/zset_family.cc
+++ b/src/server/zset_family.cc
@@ -422,10 +422,10 @@ void IntervalVisitor::ExtractSkipList(const zrangespec& range) {
 
 void IntervalVisitor::ExtractListPack(const zlexrangespec& range) {
   uint8_t* zl = (uint8_t*)zobj_->ptr;
-  uint8_t *eptr, *sptr;
-  uint8_t* vstr;
-  unsigned int vlen;
-  long long vlong;
+  uint8_t *eptr, *sptr = nullptr;
+  uint8_t* vstr = nullptr;
+  unsigned int vlen = 0;
+  long long vlong = 0;
   unsigned offset = params_.offset;
   unsigned limit = params_.limit;
 
@@ -748,6 +748,10 @@ void ZSetFamily::ZIncrBy(CmdArgList args, ConnectionContext* cntx) {
   (*cntx)->SendDouble(add_result.new_score);
 }
 
+void ZSetFamily::ZInterStore(CmdArgList args, ConnectionContext* cntx) {
+
+}
+
 void ZSetFamily::ZLexCount(CmdArgList args, ConnectionContext* cntx) {
   string_view key = ArgS(args, 1);
 
@@ -979,6 +983,19 @@ void ZSetFamily::ZScan(CmdArgList args, ConnectionContext* cntx) {
   }
 }
 
+void ZSetFamily::ZUnionStore(CmdArgList args, ConnectionContext* cntx) {
+  auto cb = [&](Transaction* t, EngineShard* es) {
+    auto args = t->ShardArgsInShard(es->shard_id());
+    for (auto x : args) {
+      LOG(INFO) << "arg " << x;
+    }
+    return OpStatus::OK;
+  };
+
+  OpStatus result = cntx->transaction->ScheduleSingleHop(std::move(cb));
+  (*cntx)->SendOk();
+}
+
 void ZSetFamily::ZRangeByScoreInternal(string_view key, string_view min_s, string_view max_s,
                                        const RangeParams& params, ConnectionContext* cntx) {
   ZRangeSpec range_spec;
@@ -1201,7 +1218,7 @@ OpStatus ZSetFamily::OpAdd(const ZParams& zparams, const OpArgs& op_args, string
   unsigned processed = 0;
 
   sds& tmp_str = op_args.shard->tmp_str1;
-  double new_score;
+  double new_score = 0;
   int retflags = 0;
 
   OpStatus res = OpStatus::OK;
@@ -1483,6 +1500,7 @@ void ZSetFamily::Register(CommandRegistry* registry) {
             << CI{"ZCARD", CO::FAST | CO::READONLY, 2, 1, 1, 1}.HFUNC(ZCard)
             << CI{"ZCOUNT", CO::FAST | CO::READONLY, 4, 1, 1, 1}.HFUNC(ZCount)
             << CI{"ZINCRBY", CO::FAST | CO::WRITE | CO::DENYOOM, 4, 1, 1, 1}.HFUNC(ZIncrBy)
+            << CI{"ZINTERSTORE", CO::WRITE | CO::DESTINATION_KEY, -4, 1, 1, 1}.HFUNC(ZInterStore)
             << CI{"ZLEXCOUNT", CO::READONLY, 4, 1, 1, 1}.HFUNC(ZLexCount)
             << CI{"ZREM", CO::FAST | CO::WRITE, -3, 1, 1, 1}.HFUNC(ZRem)
             << CI{"ZRANGE", CO::READONLY, -4, 1, 1, 1}.HFUNC(ZRange)
@@ -1496,7 +1514,8 @@ void ZSetFamily::Register(CommandRegistry* registry) {
             << CI{"ZREVRANGE", CO::READONLY, 4, 1, 1, 1}.HFUNC(ZRevRange)
             << CI{"ZREVRANGEBYSCORE", CO::READONLY, -4, 1, 1, 1}.HFUNC(ZRevRangeByScore)
             << CI{"ZREVRANK", CO::READONLY | CO::FAST, 3, 1, 1, 1}.HFUNC(ZRevRank)
-            << CI{"ZSCAN", CO::READONLY | CO::RANDOM, -3, 1, 1, 1}.HFUNC(ZScan);
+            << CI{"ZSCAN", CO::READONLY | CO::RANDOM, -3, 1, 1, 1}.HFUNC(ZScan)
+            << CI{"ZUNIONSTORE", CO::WRITE | CO::DESTINATION_KEY, -4, 3, 3, 1}.HFUNC(ZUnionStore);
 }
 
 }  // namespace dfly
diff --git a/src/server/zset_family.h b/src/server/zset_family.h
index d807b1c..dda433e 100644
--- a/src/server/zset_family.h
+++ b/src/server/zset_family.h
@@ -56,6 +56,7 @@ class ZSetFamily {
   static void ZCard(CmdArgList args, ConnectionContext* cntx);
   static void ZCount(CmdArgList args, ConnectionContext* cntx);
   static void ZIncrBy(CmdArgList args, ConnectionContext* cntx);
+  static void ZInterStore(CmdArgList args, ConnectionContext* cntx);
   static void ZLexCount(CmdArgList args, ConnectionContext* cntx);
   static void ZRange(CmdArgList args, ConnectionContext* cntx);
   static void ZRank(CmdArgList args, ConnectionContext* cntx);
@@ -70,6 +71,7 @@ class ZSetFamily {
   static void ZRevRangeByScore(CmdArgList args, ConnectionContext* cntx);
   static void ZRevRank(CmdArgList args, ConnectionContext* cntx);
   static void ZScan(CmdArgList args, ConnectionContext* cntx);
+  static void ZUnionStore(CmdArgList args, ConnectionContext* cntx);
 
   static void ZRangeByScoreInternal(std::string_view key, std::string_view min_s,
                                     std::string_view max_s, const RangeParams& params,