diff --git a/CMakeLists.txt b/CMakeLists.txt
index 428c7ba..b00cee4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,6 +11,7 @@ set(CMAKE_CXX_STANDARD 20)
 
 find_package(PkgConfig REQUIRED)
 pkg_check_modules(CMOCKA REQUIRED cmocka)
+find_package(SQLite3)
 
 add_subdirectory(coroio)
 
@@ -35,6 +36,12 @@ target_link_libraries(server miniraft coroio)
 target_link_libraries(client miniraft coroio)
 target_link_libraries(kv miniraft coroio)
 
+if (SQLite3_FOUND)
+add_executable(sql examples/sql.cpp)
+target_include_directories(sql PRIVATE ${SQLite3_INCLUDE_DIRS})
+target_link_libraries(sql PRIVATE ${SQLite3_LIBRARIES} miniraft coroio)
+endif()
+
 target_include_directories(test_raft PRIVATE ${CMOCKA_INCLUDE_DIRS})
 target_link_directories(test_raft PRIVATE ${CMOCKA_LIBRARY_DIRS})
 target_link_libraries(test_raft miniraft coroio ${CMOCKA_LIBRARIES})
diff --git a/examples/kv.cpp b/examples/kv.cpp
index 70642c2..d5935aa 100644
--- a/examples/kv.cpp
+++ b/examples/kv.cpp
@@ -51,7 +51,7 @@ TMessageHolder<TMessage> TKv::Read(TMessageHolder<TCommandRequest> message, uint
     }
 }
 
-void TKv::Write(TMessageHolder<TLogEntry> message, uint64_t index) {
+TMessageHolder<TMessage> TKv::Write(TMessageHolder<TLogEntry> message, uint64_t index) {
     if (LastAppliedIndex < index) {
         auto entry = message.Cast<TKvLogEntry>();
         std::string_view k(entry->TKvEntry::Data, entry->KeySize);
@@ -63,6 +63,7 @@ void TKv::Write(TMessageHolder<TLogEntry> message, uint64_t index) {
         }
         LastAppliedIndex = index;
     }
+    return {};
 }
 
 TMessageHolder<TLogEntry> TKv::Prepare(TMessageHolder<TCommandRequest> command, uint64_t term) {
diff --git a/examples/kv.h b/examples/kv.h
index fbde002..5df1bb7 100644
--- a/examples/kv.h
+++ b/examples/kv.h
@@ -8,7 +8,7 @@
 class TKv: public IRsm {
 public:
     TMessageHolder<TMessage> Read(TMessageHolder<TCommandRequest> message, uint64_t index) override;
-    void Write(TMessageHolder<TLogEntry> message, uint64_t index) override;
+    TMessageHolder<TMessage> Write(TMessageHolder<TLogEntry> message, uint64_t index) override;
     TMessageHolder<TLogEntry> Prepare(TMessageHolder<TCommandRequest> message, uint64_t term) override;
 
 private:
diff --git a/examples/sql.cpp b/examples/sql.cpp
new file mode 100644
index 0000000..b447834
--- /dev/null
+++ b/examples/sql.cpp
@@ -0,0 +1,323 @@
+#include <sqlite3.h>
+#include <iostream>
+
+#include <raft.h>
+#include <persist.h>
+#include <server.h>
+
+struct TSqlEntry {
+    uint32_t QuerySize = 0;
+    char Query[0];
+};
+
+struct TSqlLogEntry: public TLogEntry, public TSqlEntry
+{
+};
+
+struct TWriteSql: public TCommandRequest, public TSqlEntry
+{
+};
+
+struct TReadSql: public TCommandRequest, public TSqlEntry 
+{
+};
+
+struct TRow {
+    std::vector<std::optional<std::string>> Values;
+};
+
+struct TResult {
+    std::vector<std::string> Cols;
+    std::vector<TRow> Rows;
+
+    void Clear() {
+        Cols.clear();
+        Rows.clear();
+    }
+
+    bool Empty() {
+        return Cols.empty();
+    }
+};
+
+class TSql: public IRsm {
+public:
+    TSql(const std::string& path, int serverId);
+    ~TSql();
+
+    // select
+    TMessageHolder<TMessage> Read(TMessageHolder<TCommandRequest> message, uint64_t index) override;
+    // insert, update, create
+    TMessageHolder<TMessage> Write(TMessageHolder<TLogEntry> message, uint64_t index) override;
+    // convert request to log message
+    TMessageHolder<TLogEntry> Prepare(TMessageHolder<TCommandRequest> message, uint64_t term) override;
+
+private:
+    bool Execute(const std::string& q);
+    static int Process(void* self, int ncols, char** values, char** cols);
+    TMessageHolder<TMessage> Reply(const std::string& ans, uint64_t index);
+
+    TResult Result;
+    std::string LastError;
+    uint64_t LastAppliedIndex = 0;
+    sqlite3* Db = nullptr;
+};
+
+TSql::TSql(const std::string& path, int serverId)
+{
+    std::string dbPath = path + "." + std::to_string(serverId);
+    if (sqlite3_open(dbPath.c_str(), &Db) != SQLITE_OK) {
+        std::cerr << "Cannot open db: `" << dbPath << "', " 
+            << "error: " << sqlite3_errmsg(Db)
+            << std::endl;
+        throw std::runtime_error("Cannot open db");
+    }
+    Execute(R"__(CREATE TABLE IF NOT EXISTS raft_metadata_ (key TEXT PRIMARY KEY, value TEXT))__");
+    Execute(R"__(SELECT value FROM raft_metadata_ WHERE key = 'LastAppliedIndex')__");
+    if (!Result.Empty()) {
+        LastAppliedIndex = std::stoi(*Result.Rows[0].Values[0]);
+    }
+    std::cerr << "LastAppliedIndex: " << LastAppliedIndex << std::endl;
+}
+
+TSql::~TSql()
+{
+    if (Db) {
+        if (sqlite3_close(Db) != SQLITE_OK) {
+            std::cerr << "Failed to close db, error:" << sqlite3_errmsg(Db) << std::endl; 
+        }
+    }
+}
+
+int TSql::Process(void* self, int ncols, char** values, char** cols) {
+    TSql* this_ = (TSql*)self;
+    if (this_->Result.Cols.empty()) {
+        for (int i = 0; i < ncols; i++) {
+            this_->Result.Cols.emplace_back(cols[i]);
+        }
+    }
+    TRow row;
+    for (int i = 0; i < ncols; i++) {
+        if (values[i]) {
+            row.Values.emplace_back(values[i]);
+        } else {
+            row.Values.emplace_back(std::nullopt);
+        }
+    }
+    this_->Result.Rows.emplace_back(std::move(row));
+    return 0;
+}
+
+bool TSql::Execute(const std::string& q) {
+    char* err = nullptr;
+    std::cerr << "Execute: " << q << std::endl;
+    Result.Clear();
+    LastError.clear();
+    if (sqlite3_exec(Db, q.c_str(), Process, this, &err) != SQLITE_OK) {
+        std::cerr << "Cannot apply changes, error: " << err << std::endl;
+        LastError = err;
+        sqlite3_free(err);
+        return false;
+    }
+    std::cerr << "OK" << std::endl;
+    return true;
+}
+ 
+TMessageHolder<TMessage> TSql::Read(TMessageHolder<TCommandRequest> message, uint64_t index) {
+    auto readSql = message.Cast<TReadSql>();
+    if (!Execute(std::string(readSql->Query, readSql->QuerySize))) {
+        return Reply(LastError, index);
+    } else {
+        std::string text;
+        for (int i = 0; i < Result.Cols.size(); i++) {
+            text += Result.Cols[i];
+            if (i != Result.Cols.size() - 1) {
+                text += ",";
+            }
+        }
+        text += "\n";
+        for (int j = 0; j < Result.Rows.size(); j++) {
+            for (int i = 0; i < Result.Cols.size(); i++) {
+                text += Result.Rows[j].Values[i] ? *Result.Rows[j].Values[i] : "null";
+                if (i != Result.Cols.size() - 1) {
+                    text += ",";
+                }
+            }
+            text += "\n";
+        }
+        return Reply(text, index);
+    }
+}
+
+TMessageHolder<TMessage> TSql::Write(TMessageHolder<TLogEntry> message, uint64_t index) {
+    // TODO: index + 1 == LastAppliedIndex
+
+    std::string err;
+    if (LastAppliedIndex < index) {
+        auto entry = message.Cast<TSqlLogEntry>();
+        std::cerr << "Execute write of size: " << entry->QuerySize << std::endl;
+        std::string updateLastApplied;
+        updateLastApplied += "INSERT INTO raft_metadata_ (key, value) VALUES ('LastAppliedIndex','" + std::to_string(index) + "')\n";
+        updateLastApplied += "ON CONFLICT(key) DO UPDATE SET value = '" + std::to_string(index) + "';\n";
+        std::string q = "BEGIN TRANSACTION;\n";
+        q += std::string(entry->Query, entry->QuerySize);
+        if (q.back() != ';') {
+            q += ";\n";
+        }
+        q += updateLastApplied;
+        q += "COMMIT;";
+        if (Execute(q)) {
+            LastAppliedIndex = index;
+        } else {
+            err = LastError;
+            Execute("ROLLBACK;");
+            Execute(updateLastApplied); // need to update LastAppliedIndex in order not to execute failed query aqain
+        }
+    }
+    return Reply(err, index);
+}
+
+TMessageHolder<TMessage> TSql::Reply(const std::string& ans, uint64_t index)
+{
+    auto res = NewHoldedMessage<TCommandResponse>(sizeof(TCommandResponse)+ans.size());
+    res->Index = index;
+    memcpy(res->Data, ans.data(), ans.size());
+    return res;
+}
+
+TMessageHolder<TLogEntry> TSql::Prepare(TMessageHolder<TCommandRequest> command, uint64_t term) {
+    auto dataSize = command->Len - sizeof(TCommandRequest);
+    std::cerr << "Prepare entry of size: " << dataSize << ", in term: " << term << std::endl;
+    auto entry = NewHoldedMessage<TLogEntry>(sizeof(TLogEntry)+dataSize);
+    memcpy(entry->Data, command->Data, dataSize);
+    entry->Term = term;
+    return entry;
+}
+
+template<typename TPoller, typename TSocket>
+NNet::TFuture<void> Client(TPoller& poller, TSocket socket) {
+    using TFileHandle = typename TPoller::TFileHandle;
+    TFileHandle input{0, poller}; // stdin
+    co_await socket.Connect();
+    std::cout << "Connected\n";
+
+    NNet::TLine line;
+    TCommandRequest header;
+    header.Flags = TCommandRequest::EWrite;
+    header.Type = static_cast<uint32_t>(TCommandRequest::MessageType);
+    auto lineReader = NNet::TLineReader(input, 2*1024);
+    auto byteWriter = NNet::TByteWriter(socket);
+    const char* sep = " \t\r\n";
+
+    try {
+        while ((line = co_await lineReader.Read())) {
+            std::string strLine;
+            strLine += std::string_view(line.Part1.data(), line.Part1.size());
+            strLine += std::string_view(line.Part2.data(), line.Part2.size());
+            size_t pos = strLine.find(' ');
+            auto prefix = strLine.substr(0, pos);
+            TMessageHolder<TMessage> req;
+        
+            int flags = 0;
+            if (!strcasecmp(prefix.data(), "create") || !strcasecmp(prefix.data(), "insert") || !strcasecmp(prefix.data(), "update")) {
+                auto mes = NewHoldedMessage<TWriteSql>(sizeof(TWriteSql) + strLine.size());
+                mes->Flags = TCommandRequest::EWrite;
+                mes->QuerySize = strLine.size();
+                memcpy(mes->Query, strLine.data(), strLine.size());
+                req = mes;
+            } else if (!strcasecmp(prefix.data(), "select")) {
+                auto mes = NewHoldedMessage<TReadSql>(sizeof(TReadSql) + strLine.size());
+                mes->QuerySize = strLine.size();
+                memcpy(mes->Query, strLine.data(), strLine.size());
+                req = mes;
+            } else {
+                std::cerr << "Cannot parse command: " << strLine << std::endl;
+                continue;
+            }
+            co_await TMessageWriter(socket).Write(std::move(req));
+            auto reply = co_await TMessageReader(socket).Read();
+            auto res = reply.template Cast<TCommandResponse>();
+            auto len = res->Len - sizeof(TCommandResponse);
+            std::string_view data(res->Data, len);
+            std::cout << "commitIndex: " << res->Index << "\n";
+            if (!data.empty()) {
+                std::cout << data << "\n";
+            }
+        }
+    } catch (const std::exception& ex) {
+        std::cout << "Exception: " << ex.what() << "\n";
+    }
+    co_return;
+}
+
+void usage(const char* prog) {
+    std::cerr << prog << "--client|--server --id myid --node ip:port:id [--node ip:port:id ...]" << "\n";
+    exit(0);
+}
+
+int main(int argc, char** argv) 
+{
+    signal(SIGPIPE, SIG_IGN);
+    std::vector<THost> hosts;
+    THost myHost;
+    TNodeDict nodes;
+    uint32_t id = 0;
+    bool server = false;
+    for (int i = 1; i < argc; i++) {
+        if (!strcmp(argv[i], "--server")) {
+            server = true;
+        } else if (!strcmp(argv[i], "--node") && i < argc - 1) {
+            // address:port:id
+            hosts.push_back(THost{argv[++i]});
+        } else if (!strcmp(argv[i], "--id") && i < argc - 1) {
+            id = atoi(argv[++i]);
+        } else if (!strcmp(argv[i], "--help")) {
+            usage(argv[0]);
+        }
+    }
+
+    using TPoller = NNet::TDefaultPoller;
+    std::shared_ptr<ITimeSource> timeSource = std::make_shared<TTimeSource>();
+    NNet::TLoop<TPoller> loop;
+
+    if (server) {
+        for (auto& host : hosts) {
+            if (!host) {
+                std::cerr << "Empty host\n"; return 1;
+            }
+            if (host.Id == id) {
+                myHost = host;
+            } else {
+                nodes[host.Id] = std::make_shared<TNode<TPoller::TSocket>>(
+                    [&](const NNet::TAddress& addr) { return TPoller::TSocket(addr, loop.Poller()); },
+                    std::to_string(host.Id),
+                    NNet::TAddress{host.Address, host.Port},
+                    timeSource);
+            }
+        }
+
+        if (!myHost) {
+            std::cerr << "Host not found\n"; return 1;
+        }
+
+        std::shared_ptr<IRsm> rsm = std::make_shared<TSql>("sql_file.db", myHost.Id);
+        auto state = std::make_shared<TDiskState>("sql_state", myHost.Id);
+        auto raft = std::make_shared<TRaft>(rsm, state, myHost.Id, nodes);
+        TPoller::TSocket socket(NNet::TAddress{myHost.Address, myHost.Port}, loop.Poller());
+        socket.Bind();
+        socket.Listen();
+        TRaftServer server(loop.Poller(), std::move(socket), raft, nodes, timeSource);
+        server.Serve();
+        loop.Loop();
+    } else {
+        NNet::TAddress addr{hosts[0].Address, hosts[0].Port};
+        NNet::TSocket socket(std::move(addr), loop.Poller());
+
+        auto h = Client(loop.Poller(), std::move(socket));
+        while (!h.done()) {
+            loop.Step();
+        }
+    }
+    return 0;
+}
+
diff --git a/src/raft.cpp b/src/raft.cpp
index 25021c7..9187276 100644
--- a/src/raft.cpp
+++ b/src/raft.cpp
@@ -40,12 +40,13 @@ TMessageHolder<TMessage> TDummyRsm::Read(TMessageHolder<TCommandRequest> message
     }
 }
 
-void TDummyRsm::Write(TMessageHolder<TLogEntry> message, uint64_t index)
+TMessageHolder<TMessage> TDummyRsm::Write(TMessageHolder<TLogEntry> message, uint64_t index)
 {
     if (LastAppliedIndex < index) {
         Log.emplace_back(std::move(message));
         LastAppliedIndex = index;
     }
+    return {};
 }
 
 TMessageHolder<TLogEntry> TDummyRsm::Prepare(TMessageHolder<TCommandRequest> command, uint64_t term)
@@ -276,7 +277,7 @@ void TRaft::OnCommandRequest(TMessageHolder<TCommandRequest> command, const std:
     }
     auto index = State->LastLogIndex;
     if (replyTo) {
-        waiting.emplace(TWaiting{index, std::move(command), replyTo});
+        Waiting.emplace(TWaiting{index, std::move(command), replyTo});
     }
 }
 
@@ -386,18 +387,28 @@ void TRaft::Process(ITimeSource::Time now, TMessageHolder<TMessage> message, con
 void TRaft::ProcessCommitted() {
     auto commitIndex = VolatileState->CommitIndex;
     for (auto i = VolatileState->LastApplied+1; i <= commitIndex; i++) {
-        Rsm->Write(State->Get(i-1), i);
+        auto reply = Rsm->Write(State->Get(i-1), i);
+        WriteAnswers.emplace(TAnswer {
+            .Index = i,
+            .Reply = reply ? reply : NewHoldedMessage(TCommandResponse {.Index = i})
+        });
     }
     VolatileState->LastApplied = commitIndex;
 }
 
 void TRaft::ProcessWaiting() {
     auto lastApplied = VolatileState->LastApplied;
-    while (!waiting.empty() && waiting.top().Index <= lastApplied) {
-        auto w = waiting.top(); waiting.pop();
+    while (!Waiting.empty() && Waiting.top().Index <= lastApplied) {
+        auto w = Waiting.top(); Waiting.pop();
         TMessageHolder<TMessage> reply;
         if (w.Command->Flags & TCommandRequest::EWrite) {
-            reply = NewHoldedMessage(TCommandResponse {.Index = w.Index});
+            while (!WriteAnswers.empty() && WriteAnswers.front().Index < w.Index) {
+                WriteAnswers.pop();
+            }
+            assert(!WriteAnswers.empty());
+            auto answer = std::move(WriteAnswers.front()); WriteAnswers.pop();
+            assert(answer.Index == w.Index);
+            reply = std::move(answer.Reply);
         } else {
             reply = Rsm->Read(std::move(w.Command), w.Index);
         }
diff --git a/src/raft.h b/src/raft.h
index aed23dd..b22ae38 100644
--- a/src/raft.h
+++ b/src/raft.h
@@ -22,13 +22,13 @@ struct INode {
 struct IRsm {
     virtual ~IRsm() = default;
     virtual TMessageHolder<TMessage> Read(TMessageHolder<TCommandRequest> message, uint64_t index) = 0;
-    virtual void Write(TMessageHolder<TLogEntry> message, uint64_t index) = 0;
+    virtual TMessageHolder<TMessage> Write(TMessageHolder<TLogEntry> message, uint64_t index) = 0;
     virtual TMessageHolder<TLogEntry> Prepare(TMessageHolder<TCommandRequest> message, uint64_t term) = 0;
 };
 
 struct TDummyRsm: public IRsm {
     TMessageHolder<TMessage> Read(TMessageHolder<TCommandRequest> message, uint64_t index) override;
-    void Write(TMessageHolder<TLogEntry> message, uint64_t index) override;
+    TMessageHolder<TMessage> Write(TMessageHolder<TLogEntry> message, uint64_t index) override;
     TMessageHolder<TLogEntry> Prepare(TMessageHolder<TCommandRequest> message, uint64_t term) override;
 
 private:
@@ -148,8 +148,15 @@ class TRaft {
             return Index > other.Index;
         }
     };
-    std::priority_queue<TWaiting> waiting;
+    std::priority_queue<TWaiting> Waiting;
+    
+    struct TAnswer {
+        uint64_t Index;
+        TMessageHolder<TMessage> Reply;
+    };
+    std::queue<TAnswer> WriteAnswers;
 
     EState StateName;
     uint32_t Seed = 31337;
 };
+