xiaobaoqiu@xiaobaoqiu:~/Tools/HouseMD$ curl -L -s get.jenv.io | bash
...
xiaobaoqiu@xiaobaoqiu:~/Tools/HouseMD$ source /home/xiaobaoqiu/.jenv/bin/jenv-init.sh
...
xiaobaoqiu@xiaobaoqiu:~/Tools/HouseMD$ jenv help
...

xiaobaoqiu@xiaobaoqiu:~/Tools/HouseMD$ jenv install housemd
Installing: housemd 0.2.7
Parsing http://jenv.mvnsearch.org/candidate/housemd/download/0.2.7/Linux/x86_64

Downloading: housemd 0.2.7
...

/**
     * Sets the number of seconds the driver will wait for a
     * <code>Statement</code> object to execute to the given number of seconds.
     *By default there is no limit on the amount of time allowed for a running
     * statement to complete. If the limit is exceeded, an
     * <code>SQLTimeoutException</code> is thrown.
     * A JDBC driver must apply this limit to the <code>execute</code>,
     * <code>executeQuery</code> and <code>executeUpdate</code> methods.
     * <p>
     * <strong>Note:</strong> JDBC driver implementations may also apply this
     * limit to {@code ResultSet} methods
     * (consult your driver vendor documentation for details).
     * <p>
     * <strong>Note:</strong> In the case of {@code Statement} batching, it is
     * implementation defined as to whether the time-out is applied to
     * individual SQL commands added via the {@code addBatch} method or to
     * the entire batch of SQL commands invoked by the {@code executeBatch}
     * method (consult your driver vendor documentation for details).
     *
     * @param seconds the new query timeout limit in seconds; zero means
     *        there is no limit
     * @exception SQLException if a database access error occurs,
     * this method is called on a closed <code>Statement</code>
     *            or the condition seconds >= 0 is not satisfied
     * @see #getQueryTimeout
     */
    void setQueryTimeout(int seconds) throws SQLException;

/**
 * 设置SQL执行时间
 * 如果超时,查询被cancel,并抛出SQLTimeoutException异常
 *
 * @author: xiaobaoqiu  Date: 15-8-22 Time: 下午1:55
 */
public class SqlTimeOutFilter extends FilterEventAdapter {

    /**
     * 默认超时时间,单位秒
     * 注意不要设置太小
     */
    private static final int QUERY_TIMEOUT_THRESHOLD_SECOND = 100;

    /**
     * 超时时间,默认为QUERY_TIMEOUT_THRESHOLD_SECOND
     */
    private int timeoutThreshold = QUERY_TIMEOUT_THRESHOLD_SECOND;

    @Override
    protected void statementExecuteBefore(StatementProxy statement, String sql) {
        setQueryTimeout(statement);
        super.statementExecuteBefore(statement, sql);
    }

    @Override
    protected void statementExecuteBatchBefore(StatementProxy statement) {
        setQueryTimeout(statement);
        super.statementExecuteBatchBefore(statement);
    }

    @Override
    protected void statementExecuteUpdateBefore(StatementProxy statement, String sql) {
        setQueryTimeout(statement);
        super.statementExecuteUpdateBefore(statement, sql);
    }

    @Override
    protected void statementExecuteQueryBefore(StatementProxy statement, String sql) {
        setQueryTimeout(statement);
        super.statementExecuteQueryBefore(statement, sql);
    }

    /**
     * 设置Statement超时时间,
     * statement.setQueryTimeout单位是秒,0表示没有限制.这个函数可能会抛出SQLException异常,场景:
     *      1.数据库访问错误
     *      2.在一个已经关闭的Statement上调用这个方法
     *      3.超时时间不满足seconds >= 0的条件
     *
     * @param statement
     */
    private void setQueryTimeout(StatementProxy statement) {
        try {
            statement.setQueryTimeout(timeoutThreshold);
        }catch (SQLException se) {
            //TODO: do something
        }
    }

    public int getTimeoutThreshold() {
        return timeoutThreshold;
    }

    public void setTimeoutThreshold(int timeoutThreshold) {
        this.timeoutThreshold = timeoutThreshold;
    }
}

public void setProxyFilters(List<Filter> filters) {
        if (filters != null) {
            this.filters.addAll(filters);
        }
    }

public class DruidDataSourceFactory implements DataSourceFactory {

    @Override
    public DataSource create(String host, int port, String username, String password, String dbName, int corePoolSize,
                             int maxPoolSize, String jdbcUrlOption, boolean autoCommit) throws ResourceException {
        DruidDataSource dataSource = new DruidDataSource();//使用默认实现DruidDataSource
        //设置dataSource参数, username等

        //设置dataSource的Filter
        List<Filter> filters = Lists.newArrayList();
        SqlTimeOutFilter timeOutFilter = new SqlTimeOutFilter();
        filters.add(timeOutFilter);
        dataSource.setProxyFilters(filters);
        
        //dataSource初始化等操作
        ...

        return dataSource;
    }
}

<where>
    <choose>
        <when test="id != null">
            ...
        </when>
        ...
        <otherwise>
        and 1=2
        </otherwise>
    </choose>
</where>

/**
 * Mybatis拦截器, 拦截:
 *      select语句where条件为空
 *      update语句where条件为空
 *      delete语句where条件为空
 *
 * 处理: 目前只是打warning日志,因为项目中存在数据量很少的表读全表的情况(比如加载数据进缓存)
 *      TODO:后续考虑设置拦截器的白名单,不在白名单的触发where条件为空的直接抛出异常.
 *
 * @author: xiaobaoqiu  Date: 15-8-22 Time: 上午10:26
 */
@Intercepts({ @Signature(
        type = StatementHandler.class,
        method = "prepare",
        args = { Connection.class }) })
public class EmptyWhereInterceptor implements Interceptor {

    private static final Logger logger = LoggerFactory.getLogger(EmptyWhereInterceptor.class);

    /**
     * 拦截的 COMMAND 类型
     */
    private static final Set<String> INTERCEPTOR_COMMAND = Sets.newHashSet("select", "update", "delete");

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler handler = (StatementHandler) invocation.getTarget();

        //获取实际的StatementHandler
        if (handler instanceof RoutingStatementHandler) {
            handler = (BaseStatementHandler) ReflectUtil.getFieldValue(handler, "delegate");
        }

        //获取SqlCommandType
        String commandType = getCommandType(handler);

        if (INTERCEPTOR_COMMAND.contains(commandType)) {
            String originSql = handler.getBoundSql().getSql().toLowerCase();  //获取sql
            if (!originSql.contains("where")) {
                logger.warn("禁止使用不带where条件的SQL语句.原始SQL={}", originSql);
            }
        }

        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
    }

    /**
     * 获取Command类型,小写化返回
     *
     * @param handler
     * @return
     */
    private String getCommandType(StatementHandler handler) {
        MappedStatement mappedStatement = (MappedStatement) ReflectUtil.getFieldValue(handler, "mappedStatement");
        return mappedStatement.getSqlCommandType().toString().toLowerCase();
    }
}

/**
 * 反射工具
 *
 * @author: xiaobaoqiu  Date: 15-8-22 Time: 上午11:52
 */
public class ReflectUtil {
    public ReflectUtil() {
    }

    /**
     * 改变 Accessible,便于访问private等属性
     * @param field
     */
    private static void makeAccessible(Field field) {
        if(!Modifier.isPublic(field.getModifiers())) {
            field.setAccessible(true);
        }
    }

    /**
     * 获取 object 的字段,字段名称为filedName,获取不到返回null
     * @param object
     * @param filedName
     * @return
     */
    private static Field getDeclaredField(Object object, String filedName) {
        Class superClass = object.getClass();

        while(superClass != Object.class) {
            try {
                return superClass.getDeclaredField(filedName);
            } catch (NoSuchFieldException var4) {
                superClass = superClass.getSuperclass();
            }
        }

        return null;
    }

    /**
     * 获取object字段fieldName的值,如果字段不存在直接抛异常
     *
     * @param object
     * @param fieldName
     * @return
     */
    public static Object getFieldValue(Object object, String fieldName) {
        Field field = getDeclaredField(object, fieldName);
        if(field == null) {
            throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");
        } else {
            makeAccessible(field);
            Object result = null;

            try {
                result = field.get(object);
            } catch (IllegalAccessException var5) {
                var5.printStackTrace();
            }

            return result;
        }
    }

    /**
     * 设置object字段fieldName的值,如果字段不存在直接抛异常
     *
     * @param object
     * @param fieldName
     * @param value
     */
    public static void setFieldValue(Object object, String fieldName, Object value) {
        Field field = getDeclaredField(object, fieldName);
        if(field == null) {
            throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");
        } else {
            makeAccessible(field);

            try {
                field.set(object, value);
            } catch (IllegalAccessException var5) {
                var5.printStackTrace();
            }

        }
    }
}

Caused by: com.mysql.jdbc.PacketTooBigException: Packet for query is too large (17610152 > 16777216). You can change this value on the server by setting the max_allowed_packet' variable.

mysql> show VARIABLES like '%max_allowed_packet%';
+--------------------------+------------+
| Variable_name            | Value      |
+--------------------------+------------+
| max_allowed_packet       | 16777216   |
| slave_max_allowed_packet | 1073741824 |
+--------------------------+------------+

max_allowed_packet      = 16M

Aug  4 22:03:18  kernel: Out of memory: Kill process 21447 (java) score 81 or sacrifice child
Aug  4 22:03:18  kernel: Killed process 21447, UID 40001, (java) total-vm:4242176kB, anon-rss:711240kB, file-rss:1832kB
Aug  5 01:17:21  ntpd[1195]: synchronized to Xx.xx.xxx.xx, stratum 3
Aug  5 01:35:52  kernel: java invoked oom-killer: gfp_mask=0xd0, order=0, oom_adj=0, oom_score_adj=0
Aug  5 01:35:52  kernel: java cpuset=/ mems_allowed=0
Aug  5 01:35:52  kernel: Pid: 17391, comm: java Not tainted 2.6.32-358.23.2.el6.x86_64 #1

[baoqiu.xiao@Xxx ~]$cat /proc/26893/oom_score
76
[baoqiu.xiao@Xxx ~]$ cat /proc/14969/oom_score
82

[baoqiu.xiao@ ~]$ ps aux | grep sshd
root      1208  0.0  0.0  64116   296 ?        Ss   May28   1:47 /usr/sbin/sshd
[baoqiu.xiao@ ~]$ cat /proc/1208/oom_adj 
-17

pgrep -f "sshd" | while read PID; do echo -17 > /proc/$PID/oom_adj;done

Aug  5 01:35:52 l-crm4.des.dev.cn0 kernel: [ pid ]   uid  tgid total_vm      rss cpu oom_adj oom_score_adj name
...
Aug  5 01:35:52 l-crm4.des.dev.cn0 kernel: [ 1187]     0  1187    16029       73   2     -17         -1000 sshd
...

# sysctl -w vm.panic_on_oom=1
vm.panic_on_oom = 1   //1表示关闭，默认为0表示开启OOM
# sysctl -p