Caching over MyBatis : Memcached Performance Tuning Over MyBatis

This article represents the third  Proof of Concept from series described in the previous  article 4 Hands-On Approaches to Improve Your Data Access Layer Implementation and it presents how to implement Memcached over MyBatis, how to achieve an optim configuration for it and personal opinions of the author about the chosen approach for the Data Access Layer.

According to its website, Memcached is a  free & open source, high-performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load. This characterization describes a powerful, in-memory key-value store caching system available to us developers for free. Throughout this article, the following aspects will be addressed:

1. How will an application benefit from caching using Memcached? Memcached's features will be detailed in this section.

2. Hands-on implementation of the MemCachedPOC project - in this section the key concepts of Memcached will be explored through a hands on implementation.

3. Summary - How has the application performance been improved after this implementation?

Code of all the projects that will be implemented can be found at https://github.com/ammbra/CacherPoc   or if you are interested only in the current implementation, you can access it here : https://github.com/ammbra/CacherPoc/tree/master/MemCachedPOC 

How will an application benefit from caching using Memcached?

The 21^st century is governed by technology and speed;  release time for applications shortens by day and every week/month/year brings a major change within the IT industry. In an virtual universe that changes so fast, the web applications must serve dynamic content as quickly as possible; each millisecond matters and this is why caching is an imperative strategy for these web applications.

Memcached is among the most popular caching solutions and has in its portfolio users like

LiveJournal , Flickr, Twitter, Youtube, WordPress.com . Below are listed a few reasons for using Memcached :

•  is a system to cache data in RAM rather than in database
•  improves cache read/write performance
• can improve page load performance
• allows distributing the cache load to separate servers
• being a cache system, offers efficient resource utilization and significantly reduces database load
• given its list of clients, seems to be perfect for websites with high database load

Memcached  should be used when:

•   when static page caching is not an option.
•  have adequate server resources to allocate to Memcached without negatively impacting   other services.
• your web application has enough traffic to make a difference when caching strategy is   implemented.

 Memcached should not be used if:

• the web application has completely anonymous traffic (low traffic sites that are not straining server resources )
• static caching suits better your application (probably you  will not see any noticeable benefit when memcached is implemented and have increased the complexity of the system)
• can negatively impact performance/scalability in this case.

Hands-on implementation of the MemCachedPOC project

Our implementation of MemCachedPOC will look as described in the diagram below:

In order to test Memcached performance the following project setup is performed:

1. Create a new Maven EJB Project from your IDE (this kind of project is platform provided by NetBeans but for those that use eclipse, here is an usefull tutorial http://theopentutorials.com/examples/java-ee/ejb3/how-to-create-a-ejb-3-x-project-using-maven-in-eclipse-part-2/). In the article this project is named MemCachedPOC.

2. Edit your project's pom by adding required jars :

       <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.2.6</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis.caches</groupId>
            <artifactId>mybatis-memcached</artifactId>
            <version>1.0.0</version>
        </dependency>
        <dependency>
            <groupId>net.spy</groupId>
            <artifactId>spymemcached</artifactId>
            <version>2.10.6</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>     
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.5</version>
        </dependency>

Note: the Memcached integration for MyBatis is built on top of the spymemcached client and this is why in our pom.xml dependencies we also need the spymemcached jar.

3.Add your database connection driver, in this case apache derby:

        <dependency>
            <groupId>org.apache.derby</groupId>
            <artifactId>derbyclient</artifactId>
            <version>10.11.1.1</version>
        </dependency>

4. Run mvn clean and mvn install commands on your project.

If you have your project in place, let's go ahead with our implementation of MyBatis :

1. Configure under resources/com/tutorial/MemCachedPOC/xml folder the Configuration.xml file with :

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="UNPOOLED">
                <property name="driver" value="org.apache.derby.jdbc.ClientDriver"/>
                <property name="url" value="dburl"/>
                <property name="username" value="cruddy"/>
                <property name="password" value="cruddy"/>
            </dataSource>
        </environment>         
    </environments>
    <mappers>               
            <!--<mapper resource="com/tutorial/memcachedpoc/xml/EmployeeMapper.xml" /> -->
    </mappers>                   
</configuration>

2. Create in java your own SQLSessionFactory implementation. For example, create  com.tutorial.memcachedpoc.config. SQLSessionFactory

public class SQLSessionFactory {
    private static final SqlSessionFactory FACTORY;
 
    static {
        try {
            Reader reader = Resources.getResourceAsReader("com/tutorial/memcachedpoc/xml/Configuration.xml");
            FACTORY = new SqlSessionFactoryBuilder().build(reader);
        } catch (Exception e){
            throw new RuntimeException("Fatal Error.  Cause: " + e, e);
        }
    }
 
    public static SqlSessionFactory getSqlSessionFactory() {
        return FACTORY;
    }
}

3. Create your necessary bean classes, the ones that will map to your sql results, like Employee:

public class Employee implements Serializable {
    private static final long serialVersionUID = 1L;
    private Integer id;
    private String firstName;
    private String lastName;
    private String adress;
    private Date hiringDate;
    private String sex;
    private String phone;
    private int positionId;
    private int deptId;

    public Employee() {
    }

    public Employee(Integer id) {
        this.id = id;
    }


    @Override
    public String toString() {
        return "com.tutorial.memcachedpoc.bean.Employee[ id=" + id + " ]";
    }
}

4. Create the IEmployeeDAO interface that will expose the ejb implementation when injected:

public interface IEmployeeDAO {
        public List<Employee> getEmployees();   
}

5. Implement the above inteface:

@Stateless(name="memcachedDAO")
@TransactionManagement(TransactionManagementType.CONTAINER)
public class EmployeeDAO implements IEmployeeDAO {

    private static Logger logger = Logger.getLogger(EmployeeDAO.class);
    private SqlSessionFactory sqlSessionFactory;

   @PostConstruct
     public void init() {
        sqlSessionFactory = SQLSessionFactory.getSqlSessionFactory();
    }


    @Override
    public List<Employee> getEmployees() {
        logger.info("Getting employees using memcached.....");
        SqlSession sqlSession = sqlSessionFactory.openSession();
        List<Employee> results = sqlSession.selectList("retrieveEmployees");
        sqlSession.close();
        return results;
    }
}

6. Create the EmployeeMapper that contains the query named "retrieveEmployees"

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.tutorial.memcachedpoc.mapper.EmployeeMapper" >
    <resultMap id="results" type="com.tutorial.ehcachepoc.bean.Employee" >
        <id column="id" property="id" javaType="integer" jdbcType="BIGINT" />
        <result column="first_name" property="firstName" javaType="string" jdbcType="VARCHAR"/>
        <result column="last_name" property="lastName" javaType="string" jdbcType="VARCHAR"/>
        <result column="hiring_date" property="hiringDate" javaType="date" jdbcType="DATE" />
        <result column="sex" property="sex" javaType="string" jdbcType="VARCHAR" />
        <result column="dept_id" property="deptId" javaType="integer" jdbcType="BIGINT" />
    </resultMap> 
 
    <select id="retrieveEmployees" resultMap="results" >
        select id, first_name, last_name, hiring_date, sex, dept_id
        from employee   
    </select>  	
</mapper>

If you remember our CacherPOC setup from the previously article, then you can test your implementation if you add MemCachedPOC project as dependency and inject the IEmployeeDAO inside the MemcachedServlet. Your CacherPOC pom.xml file should contain :

      <dependency>
            <groupId>${project.groupId}</groupId>
            <artifactId>MemCachedPoc</artifactId>
            <version>${project.version}</version>
        </dependency>

and your servlet should look like:

@WebServlet("/MemCachedServlet")
public class MemCachedServlet extends HttpServlet {
   private static Logger logger = Logger.getLogger(MemCachedServlet.class);

    @EJB(beanName="memcachedDAO")
    IEmployeeDAO employeeDAO;
    private static final String LIST_USER = "/listEmployee.jsp";

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String forward= LIST_USER;
        List<Employee> results = new ArrayList<Employee>();
         for (int i = 0; i < 10; i++) {
            for (Employee emp : employeeDAO.getEmployees()) {
                logger.debug(emp);
                results.add(emp);
            }
            
            try {
                Thread.sleep(3000);
            } catch (Exception e) {
                logger.error(e, e);
            }
        }
        req.setAttribute("employees", results);
        RequestDispatcher view = req.getRequestDispatcher(forward);
        view.forward(req, resp);
    }
    
}			

Run your CacherPoc implementation to check if your Data Access Layer with MyBatis is working or download the code provided at https://github.com/ammbra/CacherPoc 

But if a great amount of employees is stored in database, or perhaps the retrieval of a  number of 10xemployeesNo represents a lot of workload for the database. Also, can be noticed that the query from the EmployeeMapper.xml retrieves data that almost never changes (id, first_name, last_name, hiring_date, sex cannot change; the only value that might change in time is dept_id); so a caching mechanism can be used.

Below is described how this can be achieved using Memcached:

Caching Step 1.  Add memcached.properties  file under resources folder and try a similar configuration for it (if this file is not defined,  if not found, the client will use the default settings):

org.mybatis.caches.memcached.keyprefix=_mybatis_
org.mybatis.caches.memcached.servers=127.0.0.1:11211
org.mybatis.caches.memcached.connectionfactory=net.spy.memcached.DefaultConnectionFactory
org.mybatis.caches.memcached.asyncget = true
org.mybatis.caches.memcached.timeout = 7500
org.mybatis.caches.memcached.timeoutunit = java.util.concurrent.TimeUnit.SECONDS

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.tutorial.memcached.mapper.EmployeeMapper" >
   
     <cache type="org.mybatis.caches.memcached.LoggingMemcachedCache" />
      
    <resultMap id="results" type="com.tutorial.memcachedpoc.bean.Employee" >
        <id column="id" property="id" javaType="integer" jdbcType="BIGINT" />
        <result column="first_name" property="firstName" javaType="string" jdbcType="VARCHAR"/>
        <result column="last_name" property="lastName" javaType="string" jdbcType="VARCHAR"/>
        <result column="adress" property="adress" javaType="string" jdbcType="VARCHAR" />
        <result column="hiring_date" property="hiringDate" javaType="date" jdbcType="DATE" />
        <result column="sex" property="sex" javaType="string" jdbcType="VARCHAR" />
        <result column="dept_id" property="deptId" javaType="integer" jdbcType="BIGINT" />
    </resultMap> 
 
    <select id="retrieveEmployees" resultMap="results" useCache="true" >
        select id, first_name, last_name, hiring_date, sex, dept_id from employee   
    </select>  
</mapper>

INFO:  2014-12-02 18:01:30,020 [EmployeeDAO] INFO  com.tutorial.memcachedpoc.dao.EmployeeDAO:38 - Getting employees.....

INFO:  2014-12-02 18:01:39,148 [JdbcTransaction] DEBUG org.apache.ibatis.transaction.jdbc.JdbcTransaction:98 - Setting autocommit to false on JDBC Connection [org.apache.derby.client.net.NetConnection40@1c374fd]

INFO:  2014-12-02 18:01:39,159 [retrieveEmployees] DEBUG com.tutorial.memcachedpoc.mapper.EmployeeMapper.retrieveEmployees:139 - ==>  Preparing: select id, first_name, last_name, hiring_date, sex, dept_id from employee

INFO:  2014-12-02 18:01:39,220 [retrieveEmployees] DEBUG com.tutorial.memcachedpoc.mapper.EmployeeMapper.retrieveEmployees:139 - ==> Parameters:

INFO:  2014-12-02 18:01:39,316 [retrieveEmployees] DEBUG com.tutorial.memcachedpoc.mapper.EmployeeMapper.retrieveEmployees:139 - <==  Total: 13

INFO:   2014-12-07 21:14:23,072 [EmployeeDAO] INFO  com.tutorial.memcachedpoc.dao.EmployeeDAO:38 - Getting employees using memcached.....
INFO:   2014-12-07 21:14:23,073 [MemcachedCache] DEBUG org.mybatis.caches.memcached.MemcachedCache:68 - Object key '-882220645:730093188:com.tutorial.memcached.mapper.EmployeeMapper.retrieveEmployees:0:2147483647:select id, first_name, last_name, hiring_date, sex, dept_id from employee' converted in '_mybatis_db1fc3c6fe8d04f626b0ef4dfcb647dab7a40494'
INFO:   2014-12-07 21:14:23,076 [MemcachedCache] DEBUG org.mybatis.caches.memcached.MemcachedCache:87 - Retrived object (_mybatis_db1fc3c6fe8d04f626b0ef4dfcb647dab7a40494, [com.tutorial.memcachedpoc.bean.Employee[ id=1 ], com.tutorial.memcachedpoc.bean.Employee[ id=2 ], com.tutorial.memcachedpoc.bean.Employee[ id=3 ], com.tutorial.memcachedpoc.bean.Employee[ id=4 ], com.tutorial.memcachedpoc.bean.Employee[ id=5 ], com.tutorial.memcachedpoc.bean.Employee[ id=6 ], com.tutorial.memcachedpoc.bean.Employee[ id=7 ], com.tutorial.memcachedpoc.bean.Employee[ id=10 ], com.tutorial.memcachedpoc.bean.Employee[ id=11 ], com.tutorial.memcachedpoc.bean.Employee[ id=12 ], com.tutorial.memcachedpoc.bean.Employee[ id=14 ], com.tutorial.memcachedpoc.bean.Employee[ id=8 ], com.tutorial.memcachedpoc.bean.Employee[ id=9 ]])
INFO:   2014-12-07 21:14:23,076 [EmployeeMapper] DEBUG com.tutorial.memcached.mapper.EmployeeMapper:62 - Cache Hit Ratio [com.tutorial.memcached.mapper.EmployeeMapper]: 0.9523809523809523
INFO:   2014-12-07 21:14:23,077 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=1 ]
INFO:   2014-12-07 21:14:23,077 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=2 ]
INFO:   2014-12-07 21:14:23,077 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=3 ]
INFO:   2014-12-07 21:14:23,077 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=4 ]
INFO:   2014-12-07 21:14:23,078 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=5 ]
INFO:   2014-12-07 21:14:23,078 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=6 ]
INFO:   2014-12-07 21:14:23,078 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=7 ]
INFO:   2014-12-07 21:14:23,078 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=10 ]
INFO:   2014-12-07 21:14:23,079 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=11 ]
INFO:   2014-12-07 21:14:23,079 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=12 ]
INFO:   2014-12-07 21:14:23,079 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=14 ]
INFO:   2014-12-07 21:14:23,079 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=8 ]
INFO:   2014-12-07 21:14:23,079 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=9 ]
INFO:   2014-12-07 21:14:26,079 [EmployeeDAO] INFO  com.tutorial.memcachedpoc.dao.EmployeeDAO:38 - Getting employees using memcached.....
INFO:   2014-12-07 21:14:26,080 [MemcachedCache] DEBUG org.mybatis.caches.memcached.MemcachedCache:68 - Object key '-882220645:730093188:com.tutorial.memcached.mapper.EmployeeMapper.retrieveEmployees:0:2147483647:select id, first_name, last_name, hiring_date, sex, dept_id from employee' converted in '_mybatis_db1fc3c6fe8d04f626b0ef4dfcb647dab7a40494'
INFO:   2014-12-07 21:14:26,082 [MemcachedCache] DEBUG org.mybatis.caches.memcached.MemcachedCache:87 - Retrived object (_mybatis_db1fc3c6fe8d04f626b0ef4dfcb647dab7a40494, [com.tutorial.memcachedpoc.bean.Employee[ id=1 ], com.tutorial.memcachedpoc.bean.Employee[ id=2 ], com.tutorial.memcachedpoc.bean.Employee[ id=3 ], com.tutorial.memcachedpoc.bean.Employee[ id=4 ], com.tutorial.memcachedpoc.bean.Employee[ id=5 ], com.tutorial.memcachedpoc.bean.Employee[ id=6 ], com.tutorial.memcachedpoc.bean.Employee[ id=7 ], com.tutorial.memcachedpoc.bean.Employee[ id=10 ], com.tutorial.memcachedpoc.bean.Employee[ id=11 ], com.tutorial.memcachedpoc.bean.Employee[ id=12 ], com.tutorial.memcachedpoc.bean.Employee[ id=14 ], com.tutorial.memcachedpoc.bean.Employee[ id=8 ], com.tutorial.memcachedpoc.bean.Employee[ id=9 ]])
INFO:   2014-12-07 21:14:26,083 [EmployeeMapper] DEBUG com.tutorial.memcached.mapper.EmployeeMapper:62 - Cache Hit Ratio [com.tutorial.memcached.mapper.EmployeeMapper]: 0.9545454545454546
INFO:   2014-12-07 21:14:26,084 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=1 ]
INFO:   2014-12-07 21:14:26,084 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=2 ]
INFO:   2014-12-07 21:14:26,084 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=3 ]
INFO:   2014-12-07 21:14:26,085 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=4 ]
INFO:   2014-12-07 21:14:26,085 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=5 ]
INFO:   2014-12-07 21:14:26,085 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=6 ]
INFO:   2014-12-07 21:14:26,085 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=7 ]
INFO:   2014-12-07 21:14:26,086 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=10 ]
INFO:   2014-12-07 21:14:26,086 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=11 ]
INFO:   2014-12-07 21:14:26,086 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=12 ]
INFO:   2014-12-07 21:14:26,087 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=14 ]
INFO:   2014-12-07 21:14:26,087 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=8 ]
INFO:   2014-12-07 21:14:26,087 [MemCachedServlet] DEBUG com.tutorial.cacherpoc.MemCachedServlet:42 - com.tutorial.memcachedpoc.bean.Employee[ id=9 ]

Let's look at the time that each of our 10 times requests has scored:

the first not cached  10 times requests took about  57seconds and 51 milliseconds , while the cached requests scored a time of 27seconds and 15 miliseconds.

In order to apply Amdhal's law for the system the following input is needed:

• Un-cached page time:  60 seconds
• Database time (S): 58 seconds
• Cache retrieval time: 27 seconds
• Proportion: 96.6% (58/60) (P)

The expected system speedup is thus:

 1 / (( 1 – 0.966) + 0.966 / (58/27)) = 1 / (0.034 + 0.966 /2.14) = 2.083 times system speedup

This result can be improved of course, but the purpose of this article was to proove that caching using Memcached over MyBatis offers a significant improvement to what used to be available before its implementation.

Learn more from:

• MyBatis Documentation
• MyBatis Memcached Adapter
• Memcached website

This article is dedicated to the memory of my mother to whom I owe everything that I am.