/*
 * Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
 * and the EPL 1.0 (http://h2database.com/html/license.html).
 * Initial Developer: H2 Group
 */
package org.h2.engine;

import java.io.IOException;
import java.net.Socket;
import java.sql.SQLException;
import java.util.ArrayList;

import org.h2.api.DatabaseEventListener;
import org.h2.api.ErrorCode;
import org.h2.api.JavaObjectSerializer;
import org.h2.command.CommandInterface;
import org.h2.command.CommandRemote;
import org.h2.command.dml.SetTypes;
import org.h2.jdbc.JdbcException;
import org.h2.message.DbException;
import org.h2.message.Trace;
import org.h2.message.TraceSystem;
import org.h2.result.ResultInterface;
import org.h2.store.DataHandler;
import org.h2.store.FileStore;
import org.h2.store.LobStorageFrontend;
import org.h2.store.LobStorageInterface;
import org.h2.store.fs.FileUtils;
import org.h2.util.JdbcUtils;
import org.h2.util.MathUtils;
import org.h2.util.NetUtils;
import org.h2.util.SmallLRUCache;
import org.h2.util.StringUtils;
import org.h2.util.TempFileDeleter;
import org.h2.util.Utils;
import org.h2.value.CompareMode;
import org.h2.value.Transfer;
import org.h2.value.Value;

The client side part of a session when using the server mode. This object
communicates with a Session on the server side.
/**
 * The client side part of a session when using the server mode. This object
 * communicates with a Session on the server side.
 */
public class SessionRemote extends SessionWithState implements DataHandler {

    public static final int SESSION_PREPARE = 0;
    public static final int SESSION_CLOSE = 1;
    public static final int COMMAND_EXECUTE_QUERY = 2;
    public static final int COMMAND_EXECUTE_UPDATE = 3;
    public static final int COMMAND_CLOSE = 4;
    public static final int RESULT_FETCH_ROWS = 5;
    public static final int RESULT_RESET = 6;
    public static final int RESULT_CLOSE = 7;
    public static final int COMMAND_COMMIT = 8;
    public static final int CHANGE_ID = 9;
    public static final int COMMAND_GET_META_DATA = 10;
    public static final int SESSION_PREPARE_READ_PARAMS = 11;
    public static final int SESSION_SET_ID = 12;
    public static final int SESSION_CANCEL_STATEMENT = 13;
    public static final int SESSION_CHECK_KEY = 14;
    public static final int SESSION_SET_AUTOCOMMIT = 15;
    public static final int SESSION_HAS_PENDING_TRANSACTION = 16;
    public static final int LOB_READ = 17;
    public static final int SESSION_PREPARE_READ_PARAMS2 = 18;

    public static final int STATUS_ERROR = 0;
    public static final int STATUS_OK = 1;
    public static final int STATUS_CLOSED = 2;
    public static final int STATUS_OK_STATE_CHANGED = 3;

    private static SessionFactory sessionFactory;

    private TraceSystem traceSystem;
    private Trace trace;
    private ArrayList<Transfer> transferList = Utils.newSmallArrayList();
    private int nextId;
    private boolean autoCommit = true;
    private ConnectionInfo connectionInfo;
    private String databaseName;
    private String cipher;
    private byte[] fileEncryptionKey;
    private final Object lobSyncObject = new Object();
    private String sessionId;
    private int clientVersion;
    private boolean autoReconnect;
    private int lastReconnect;
    private SessionInterface embedded;
    private DatabaseEventListener eventListener;
    private LobStorageFrontend lobStorage;
    private boolean cluster;
    private TempFileDeleter tempFileDeleter;

    private JavaObjectSerializer javaObjectSerializer;
    private volatile boolean javaObjectSerializerInitialized;

    private final CompareMode compareMode = CompareMode.getInstance(null, 0);

    public SessionRemote(ConnectionInfo ci) {
        this.connectionInfo = ci;
    }

    @Override
    public ArrayList<String> getClusterServers() {
        ArrayList<String> serverList = new ArrayList<>();
        for (Transfer transfer : transferList) {
            serverList.add(transfer.getSocket().getInetAddress().
                    getHostAddress() + ":" +
                    transfer.getSocket().getPort());
        }
        return serverList;
    }

    private Transfer initTransfer(ConnectionInfo ci, String db, String server)
            throws IOException {
        Socket socket = NetUtils.createSocket(server,
                Constants.DEFAULT_TCP_PORT, ci.isSSL());
        Transfer trans = new Transfer(this, socket);
        trans.setSSL(ci.isSSL());
        trans.init();
        trans.writeInt(Constants.TCP_PROTOCOL_VERSION_MIN_SUPPORTED);
        trans.writeInt(Constants.TCP_PROTOCOL_VERSION_MAX_SUPPORTED);
        trans.writeString(db);
        trans.writeString(ci.getOriginalURL());
        trans.writeString(ci.getUserName());
        trans.writeBytes(ci.getUserPasswordHash());
        trans.writeBytes(ci.getFilePasswordHash());
        String[] keys = ci.getKeys();
        trans.writeInt(keys.length);
        for (String key : keys) {
            trans.writeString(key).writeString(ci.getProperty(key));
        }
        try {
            done(trans);
            clientVersion = trans.readInt();
            trans.setVersion(clientVersion);
            if (clientVersion >= Constants.TCP_PROTOCOL_VERSION_14) {
                if (ci.getFileEncryptionKey() != null) {
                    trans.writeBytes(ci.getFileEncryptionKey());
                }
            }
            trans.writeInt(SessionRemote.SESSION_SET_ID);
            trans.writeString(sessionId);
            done(trans);
            if (clientVersion >= Constants.TCP_PROTOCOL_VERSION_15) {
                autoCommit = trans.readBoolean();
            } else {
                autoCommit = true;
            }
            return trans;
        } catch (DbException e) {
            trans.close();
            throw e;
        }
    }

    @Override
    public boolean hasPendingTransaction() {
        if (clientVersion < Constants.TCP_PROTOCOL_VERSION_10) {
            return true;
        }
        for (int i = 0, count = 0; i < transferList.size(); i++) {
            Transfer transfer = transferList.get(i);
            try {
                traceOperation("SESSION_HAS_PENDING_TRANSACTION", 0);
                transfer.writeInt(
                        SessionRemote.SESSION_HAS_PENDING_TRANSACTION);
                done(transfer);
                return transfer.readInt() != 0;
            } catch (IOException e) {
                removeServer(e, i--, ++count);
            }
        }
        return true;
    }

    @Override
    public void cancel() {
        // this method is called when closing the connection
        // the statement that is currently running is not canceled in this case
        // however Statement.cancel is supported
    }

    
Cancel the statement with the given id.
Params:
id – the statement id/**
     * Cancel the statement with the given id.
     *
     * @param id the statement id
     */
    public void cancelStatement(int id) {
        for (Transfer transfer : transferList) {
            try {
                Transfer trans = transfer.openNewConnection();
                trans.init();
                trans.writeInt(clientVersion);
                trans.writeInt(clientVersion);
                trans.writeString(null);
                trans.writeString(null);
                trans.writeString(sessionId);
                trans.writeInt(SessionRemote.SESSION_CANCEL_STATEMENT);
                trans.writeInt(id);
                trans.close();
            } catch (IOException e) {
                trace.debug(e, "could not cancel statement");
            }
        }
    }

    private void checkClusterDisableAutoCommit(String serverList) {
        if (autoCommit && transferList.size() > 1) {
            setAutoCommitSend(false);
            CommandInterface c = prepareCommand(
                    "SET CLUSTER " + serverList, Integer.MAX_VALUE);
            // this will set autoCommit to false
            c.executeUpdate(false);
            // so we need to switch it on
            autoCommit = true;
            cluster = true;
        }
    }

    public int getClientVersion() {
        return clientVersion;
    }

    @Override
    public boolean getAutoCommit() {
        return autoCommit;
    }

    @Override
    public void setAutoCommit(boolean autoCommit) {
        if (!cluster) {
            setAutoCommitSend(autoCommit);
        }
        this.autoCommit = autoCommit;
    }

    public void setAutoCommitFromServer(boolean autoCommit) {
        if (cluster) {
            if (autoCommit) {
                // the user executed SET AUTOCOMMIT TRUE
                setAutoCommitSend(false);
                this.autoCommit = true;
            }
        } else {
            this.autoCommit = autoCommit;
        }
    }

    private synchronized void setAutoCommitSend(boolean autoCommit) {
        for (int i = 0, count = 0; i < transferList.size(); i++) {
            Transfer transfer = transferList.get(i);
            try {
                traceOperation("SESSION_SET_AUTOCOMMIT", autoCommit ? 1 : 0);
                transfer.writeInt(SessionRemote.SESSION_SET_AUTOCOMMIT).
                        writeBoolean(autoCommit);
                done(transfer);
            } catch (IOException e) {
                removeServer(e, i--, ++count);
            }
        }
    }

    
Calls COMMIT if the session is in cluster mode.
/**
     * Calls COMMIT if the session is in cluster mode.
     */
    public void autoCommitIfCluster() {
        if (autoCommit && cluster) {
            // server side auto commit is off because of race conditions
            // (update set id=1 where id=0, but update set id=2 where id=0 is
            // faster)
            for (int i = 0, count = 0; i < transferList.size(); i++) {
                Transfer transfer = transferList.get(i);
                try {
                    traceOperation("COMMAND_COMMIT", 0);
                    transfer.writeInt(SessionRemote.COMMAND_COMMIT);
                    done(transfer);
                } catch (IOException e) {
                    removeServer(e, i--, ++count);
                }
            }
        }
    }

    private String getFilePrefix(String dir) {
        StringBuilder buff = new StringBuilder(dir);
        buff.append('/');
        for (int i = 0; i < databaseName.length(); i++) {
            char ch = databaseName.charAt(i);
            if (Character.isLetterOrDigit(ch)) {
                buff.append(ch);
            } else {
                buff.append('_');
            }
        }
        return buff.toString();
    }

    @Override
    public int getPowerOffCount() {
        return 0;
    }

    @Override
    public void setPowerOffCount(int count) {
        throw DbException.getUnsupportedException("remote");
    }

    
Open a new (remote or embedded) session.
Params:
openNew – whether to open a new session in any case
Returns:
the session/**
     * Open a new (remote or embedded) session.
     *
     * @param openNew whether to open a new session in any case
     * @return the session
     */
    public SessionInterface connectEmbeddedOrServer(boolean openNew) {
        ConnectionInfo ci = connectionInfo;
        if (ci.isRemote()) {
            connectServer(ci);
            return this;
        }
        // create the session using reflection,
        // so that the JDBC layer can be compiled without it
        boolean autoServerMode = ci.getProperty("AUTO_SERVER", false);
        ConnectionInfo backup = null;
        try {
            if (autoServerMode) {
                backup = ci.clone();
                connectionInfo = ci.clone();
            }
            if (openNew) {
                ci.setProperty("OPEN_NEW", "true");
            }
            if (sessionFactory == null) {
                sessionFactory = (SessionFactory) Class.forName(
                        "org.h2.engine.Engine").getMethod("getInstance").invoke(null);
            }
            return sessionFactory.createSession(ci);
        } catch (Exception re) {
            DbException e = DbException.convert(re);
            if (e.getErrorCode() == ErrorCode.DATABASE_ALREADY_OPEN_1) {
                if (autoServerMode) {
                    String serverKey = ((JdbcException) e.getSQLException()).getSQL();
                    if (serverKey != null) {
                        backup.setServerKey(serverKey);
                        // OPEN_NEW must be removed now, otherwise
                        // opening a session with AUTO_SERVER fails
                        // if another connection is already open
                        backup.removeProperty("OPEN_NEW", null);
                        connectServer(backup);
                        return this;
                    }
                }
            }
            throw e;
        }
    }

    private void connectServer(ConnectionInfo ci) {
        String name = ci.getName();
        if (name.startsWith("//")) {
            name = name.substring("//".length());
        }
        int idx = name.indexOf('/');
        if (idx < 0) {
            throw ci.getFormatException();
        }
        databaseName = name.substring(idx + 1);
        String server = name.substring(0, idx);
        traceSystem = new TraceSystem(null);
        String traceLevelFile = ci.getProperty(
                SetTypes.TRACE_LEVEL_FILE, null);
        if (traceLevelFile != null) {
            int level = Integer.parseInt(traceLevelFile);
            String prefix = getFilePrefix(
                    SysProperties.CLIENT_TRACE_DIRECTORY);
            try {
                traceSystem.setLevelFile(level);
                if (level > 0 && level < 4) {
                    String file = FileUtils.createTempFile(prefix,
                            Constants.SUFFIX_TRACE_FILE, false);
                    traceSystem.setFileName(file);
                }
            } catch (IOException e) {
                throw DbException.convertIOException(e, prefix);
            }
        }
        String traceLevelSystemOut = ci.getProperty(
                SetTypes.TRACE_LEVEL_SYSTEM_OUT, null);
        if (traceLevelSystemOut != null) {
            int level = Integer.parseInt(traceLevelSystemOut);
            traceSystem.setLevelSystemOut(level);
        }
        trace = traceSystem.getTrace(Trace.JDBC);
        String serverList = null;
        if (server.indexOf(',') >= 0) {
            serverList = StringUtils.quoteStringSQL(server);
            ci.setProperty("CLUSTER", Constants.CLUSTERING_ENABLED);
        }
        autoReconnect = ci.getProperty("AUTO_RECONNECT", false);
        // AUTO_SERVER implies AUTO_RECONNECT
        boolean autoServer = ci.getProperty("AUTO_SERVER", false);
        if (autoServer && serverList != null) {
            throw DbException
                    .getUnsupportedException("autoServer && serverList != null");
        }
        autoReconnect |= autoServer;
        if (autoReconnect) {
            String className = ci.getProperty("DATABASE_EVENT_LISTENER");
            if (className != null) {
                className = StringUtils.trim(className, true, true, "'");
                try {
                    eventListener = (DatabaseEventListener) JdbcUtils
                            .loadUserClass(className).getDeclaredConstructor().newInstance();
                } catch (Throwable e) {
                    throw DbException.convert(e);
                }
            }
        }
        cipher = ci.getProperty("CIPHER");
        if (cipher != null) {
            fileEncryptionKey = MathUtils.secureRandomBytes(32);
        }
        String[] servers = StringUtils.arraySplit(server, ',', true);
        int len = servers.length;
        transferList.clear();
        sessionId = StringUtils.convertBytesToHex(MathUtils.secureRandomBytes(32));
        // TODO cluster: support more than 2 connections
        boolean switchOffCluster = false;
        try {
            for (String s : servers) {
                try {
                    Transfer trans = initTransfer(ci, databaseName, s);
                    transferList.add(trans);
                } catch (IOException e) {
                    if (len == 1) {
                        throw DbException.get(ErrorCode.CONNECTION_BROKEN_1, e, e + ": " + s);
                    }
                    switchOffCluster = true;
                }
            }
            checkClosed();
            if (switchOffCluster) {
                switchOffCluster();
            }
            checkClusterDisableAutoCommit(serverList);
        } catch (DbException e) {
            traceSystem.close();
            throw e;
        }
    }

    private void switchOffCluster() {
        CommandInterface ci = prepareCommand("SET CLUSTER ''", Integer.MAX_VALUE);
        ci.executeUpdate(false);
    }

    
Remove a server from the list of cluster nodes and disables the cluster
mode.
Params:
e – the exception (used for debugging)
i – the index of the server to remove
count – the retry count index/**
     * Remove a server from the list of cluster nodes and disables the cluster
     * mode.
     *
     * @param e the exception (used for debugging)
     * @param i the index of the server to remove
     * @param count the retry count index
     */
    public void removeServer(IOException e, int i, int count) {
        trace.debug(e, "removing server because of exception");
        transferList.remove(i);
        if (transferList.isEmpty() && autoReconnect(count)) {
            return;
        }
        checkClosed();
        switchOffCluster();
    }

    @Override
    public synchronized CommandInterface prepareCommand(String sql, int fetchSize) {
        checkClosed();
        return new CommandRemote(this, transferList, sql, fetchSize);
    }

    
Automatically re-connect if necessary and if configured to do so.
Params:
count – the retry count index
Returns:
true if reconnected/**
     * Automatically re-connect if necessary and if configured to do so.
     *
     * @param count the retry count index
     * @return true if reconnected
     */
    private boolean autoReconnect(int count) {
        if (!isClosed()) {
            return false;
        }
        if (!autoReconnect) {
            return false;
        }
        if (!cluster && !autoCommit) {
            return false;
        }
        if (count > SysProperties.MAX_RECONNECT) {
            return false;
        }
        lastReconnect++;
        while (true) {
            try {
                embedded = connectEmbeddedOrServer(false);
                break;
            } catch (DbException e) {
                if (e.getErrorCode() != ErrorCode.DATABASE_IS_IN_EXCLUSIVE_MODE) {
                    throw e;
                }
                // exclusive mode: re-try endlessly
                try {
                    Thread.sleep(500);
                } catch (Exception e2) {
                    // ignore
                }
            }
        }
        if (embedded == this) {
            // connected to a server somewhere else
            embedded = null;
        } else {
            // opened an embedded connection now -
            // must connect to this database in server mode
            // unfortunately
            connectEmbeddedOrServer(true);
        }
        recreateSessionState();
        if (eventListener != null) {
            eventListener.setProgress(DatabaseEventListener.STATE_RECONNECTED,
                    databaseName, count, SysProperties.MAX_RECONNECT);
        }
        return true;
    }

    
Check if this session is closed and throws an exception if so.
Throws:
DbException – if the session is closed/**
     * Check if this session is closed and throws an exception if so.
     *
     * @throws DbException if the session is closed
     */
    public void checkClosed() {
        if (isClosed()) {
            throw DbException.get(ErrorCode.CONNECTION_BROKEN_1, "session closed");
        }
    }

    @Override
    public void close() {
        RuntimeException closeError = null;
        if (transferList != null) {
            synchronized (this) {
                for (Transfer transfer : transferList) {
                    try {
                        traceOperation("SESSION_CLOSE", 0);
                        transfer.writeInt(SessionRemote.SESSION_CLOSE);
                        done(transfer);
                        transfer.close();
                    } catch (RuntimeException e) {
                        trace.error(e, "close");
                        closeError = e;
                    } catch (Exception e) {
                        trace.error(e, "close");
                    }
                }
            }
            transferList = null;
        }
        traceSystem.close();
        if (embedded != null) {
            embedded.close();
            embedded = null;
        }
        if (closeError != null) {
            throw closeError;
        }
    }

    @Override
    public Trace getTrace() {
        return traceSystem.getTrace(Trace.JDBC);
    }

    public int getNextId() {
        return nextId++;
    }

    public int getCurrentId() {
        return nextId;
    }

    
Called to flush the output after data has been sent to the server and
just before receiving data. This method also reads the status code from
the server and throws any exception the server sent.
Params:
transfer – the transfer object
Throws:
DbException – if the server sent an exception
IOException – if there is a communication problem between client
            and server/**
     * Called to flush the output after data has been sent to the server and
     * just before receiving data. This method also reads the status code from
     * the server and throws any exception the server sent.
     *
     * @param transfer the transfer object
     * @throws DbException if the server sent an exception
     * @throws IOException if there is a communication problem between client
     *             and server
     */
    public void done(Transfer transfer) throws IOException {
        transfer.flush();
        int status = transfer.readInt();
        if (status == STATUS_ERROR) {
            String sqlstate = transfer.readString();
            String message = transfer.readString();
            String sql = transfer.readString();
            int errorCode = transfer.readInt();
            String stackTrace = transfer.readString();
            SQLException s = DbException.getJdbcSQLException(message, sql, sqlstate, errorCode, null, stackTrace);
            if (errorCode == ErrorCode.CONNECTION_BROKEN_1) {
                // allow re-connect
                throw new IOException(s.toString(), s);
            }
            throw DbException.convert(s);
        } else if (status == STATUS_CLOSED) {
            transferList = null;
        } else if (status == STATUS_OK_STATE_CHANGED) {
            sessionStateChanged = true;
        } else if (status == STATUS_OK) {
            // ok
        } else {
            throw DbException.get(ErrorCode.CONNECTION_BROKEN_1,
                    "unexpected status " + status);
        }
    }

    
Returns true if the connection was opened in cluster mode.
Returns:
true if it is/**
     * Returns true if the connection was opened in cluster mode.
     *
     * @return true if it is
     */
    public boolean isClustered() {
        return cluster;
    }

    @Override
    public boolean isClosed() {
        return transferList == null || transferList.isEmpty();
    }

    
Write the operation to the trace system if debug trace is enabled.
Params:
operation – the operation performed
id – the id of the operation/**
     * Write the operation to the trace system if debug trace is enabled.
     *
     * @param operation the operation performed
     * @param id the id of the operation
     */
    public void traceOperation(String operation, int id) {
        if (trace.isDebugEnabled()) {
            trace.debug("{0} {1}", operation, id);
        }
    }

    @Override
    public void checkPowerOff() {
        // ok
    }

    @Override
    public void checkWritingAllowed() {
        // ok
    }

    @Override
    public String getDatabasePath() {
        return "";
    }

    @Override
    public String getLobCompressionAlgorithm(int type) {
        return null;
    }

    @Override
    public int getMaxLengthInplaceLob() {
        return SysProperties.LOB_CLIENT_MAX_SIZE_MEMORY;
    }

    @Override
    public FileStore openFile(String name, String mode, boolean mustExist) {
        if (mustExist && !FileUtils.exists(name)) {
            throw DbException.get(ErrorCode.FILE_NOT_FOUND_1, name);
        }
        FileStore store;
        if (cipher == null) {
            store = FileStore.open(this, name, mode);
        } else {
            store = FileStore.open(this, name, mode, cipher, fileEncryptionKey, 0);
        }
        store.setCheckedWriting(false);
        try {
            store.init();
        } catch (DbException e) {
            store.closeSilently();
            throw e;
        }
        return store;
    }

    @Override
    public DataHandler getDataHandler() {
        return this;
    }

    @Override
    public Object getLobSyncObject() {
        return lobSyncObject;
    }

    @Override
    public SmallLRUCache<String, String[]> getLobFileListCache() {
        return null;
    }

    public int getLastReconnect() {
        return lastReconnect;
    }

    @Override
    public TempFileDeleter getTempFileDeleter() {
        if (tempFileDeleter == null) {
            tempFileDeleter = TempFileDeleter.getInstance();
        }
        return tempFileDeleter;
    }

    @Override
    public boolean isReconnectNeeded(boolean write) {
        return false;
    }

    @Override
    public SessionInterface reconnect(boolean write) {
        return this;
    }

    @Override
    public void afterWriting() {
        // nothing to do
    }

    @Override
    public LobStorageInterface getLobStorage() {
        if (lobStorage == null) {
            lobStorage = new LobStorageFrontend(this);
        }
        return lobStorage;
    }

    @Override
    public synchronized int readLob(long lobId, byte[] hmac, long offset,
            byte[] buff, int off, int length) {
        checkClosed();
        for (int i = 0, count = 0; i < transferList.size(); i++) {
            Transfer transfer = transferList.get(i);
            try {
                traceOperation("LOB_READ", (int) lobId);
                transfer.writeInt(SessionRemote.LOB_READ);
                transfer.writeLong(lobId);
                if (clientVersion >= Constants.TCP_PROTOCOL_VERSION_12) {
                    transfer.writeBytes(hmac);
                }
                transfer.writeLong(offset);
                transfer.writeInt(length);
                done(transfer);
                length = transfer.readInt();
                if (length <= 0) {
                    return length;
                }
                transfer.readBytes(buff, off, length);
                return length;
            } catch (IOException e) {
                removeServer(e, i--, ++count);
            }
        }
        return 1;
    }

    @Override
    public JavaObjectSerializer getJavaObjectSerializer() {
        initJavaObjectSerializer();
        return javaObjectSerializer;
    }

    private void initJavaObjectSerializer() {
        if (javaObjectSerializerInitialized) {
            return;
        }
        synchronized (this) {
            if (javaObjectSerializerInitialized) {
                return;
            }
            String serializerFQN = readSerializationSettings();
            if (serializerFQN != null) {
                serializerFQN = serializerFQN.trim();
                if (!serializerFQN.isEmpty() && !serializerFQN.equals("null")) {
                    try {
                        javaObjectSerializer = (JavaObjectSerializer) JdbcUtils
                                .loadUserClass(serializerFQN).getDeclaredConstructor().newInstance();
                    } catch (Exception e) {
                        throw DbException.convert(e);
                    }
                }
            }
            javaObjectSerializerInitialized = true;
        }
    }

    
Read the serializer name from the persistent database settings.
Returns:
the serializer/**
     * Read the serializer name from the persistent database settings.
     *
     * @return the serializer
     */
    private String readSerializationSettings() {
        String javaObjectSerializerFQN = null;
        CommandInterface ci = prepareCommand(
                "SELECT VALUE FROM INFORMATION_SCHEMA.SETTINGS "+
                " WHERE NAME='JAVA_OBJECT_SERIALIZER'", Integer.MAX_VALUE);
        try {
            ResultInterface result = ci.executeQuery(0, false);
            if (result.next()) {
                Value[] row = result.currentRow();
                javaObjectSerializerFQN = row[0].getString();
            }
        } finally {
            ci.close();
        }
        return javaObjectSerializerFQN;
    }

    @Override
    public void addTemporaryLob(Value v) {
        // do nothing
    }

    @Override
    public CompareMode getCompareMode() {
        return compareMode;
    }

    @Override
    public boolean isRemote() {
        return true;
    }

    @Override
    public String getCurrentSchemaName() {
        throw DbException.getUnsupportedException("getSchema && remote session");
    }

    @Override
    public void setCurrentSchemaName(String schema) {
        throw DbException.getUnsupportedException("setSchema && remote session");
    }

    @Override
    public boolean isSupportsGeneratedKeys() {
        return getClientVersion() >= Constants.TCP_PROTOCOL_VERSION_17;
    }

}