Java 8 full GC and OutOfMemory Java heap of space

Question

Using VisualVM and checking the Tomcat 8.5 directory catalina.out, I see that almost every time (7 out of 11 times or so) when the full GC shows that the logs show OutOfMemory (from the same minute).

With Tomcat options that have something to do with memory management: -Xms3G -Xmx = 6G -XX: + UseG1GC -XX: + UseStringDeduplication -XX: MaxHeapFreeRatio = 100 >

At first I thought it was due to the default value -XX: MaxHeapFreeRatio , which is 70 , since I saw that max. the heap size (and, of course, the heap heap) will significantly decrease during the full GC - up to ~ 10-20%. However, adding XX: MaxHeapFreeRatio = 100 did not fix it.

Although this is a graph of memory usage with a different set of JVM parameters (it cannot be obtained by someone who has old JVM ATM parameters), it is similarly growing rapidly after using full memory , the same max. heap size and max. the heap size does not fall.

Any ideas why this might happen?

: , GC OutOfMemory , - ~ 5 . , 6 .

Answer 1

, . VisualVM .

Answer 2

- MapDB.

, :

import java.io.File;
import java.io.IOException;
import java.util.Map;
import org.mapdb.DB;
import org.mapdb.DBMaker;

/**
 * Singleton class.
 */
public class DBManager 
{
        /**
     * Variables.
     */
    private static File dbFile = new File("path/to/file");
    private DB db;
    private static final String password = "yourPassword";
    private Map<Integer, String> ctDB;
    private static DBManager manager;

   /**
    * Singleton operations.
    */

  /**
   * Static initializer.
   */
  static
  {
     manager = null;
  }

/**
 * Singleton method @see DBManager.getInstance(File dbFile);
 * @return          ->  An object / instance of this class.
 */
public static DBManager getInstance()
{       
    if(isFileDatabaseOK())
    {
        /**
         * Check if an object/instance from this class exists already. 
         */
        if(manager == null)
        {
            manager = new DBManager();
        }

        /**
         * Return an object/instance of this class.
         */
        return manager;
    }
    else
    {
        return null;
    }
}

/**
 * Constructors.
 */

/**
 * Empty default Constructor starts the MapDB instance.
 */
private DBManager() 
{       
    /**
     * Load the database file from the given path
     * and initialize the database.
     */
    initMapDB();
}

/**
 * MapDB initializer.
 */

/**
 * Initialize a MapDB database.
 */
private void initMapDB() 
{
    /**
     * Persistence: Make MapDB able to load the same database from the 
     * file after JVM-Shutdown. Initialize database without @see     org.mapdb.DBMaker.deleteFilesAfterClose()
     * @see <link>https://groups.google.com/forum/#!topic/mapdb/AW8Ax49TLUc</link>
     */
    db = DBMaker.newFileDB(dbFile)
            .closeOnJvmShutdown()       
            .asyncWriteDisable()
            .encryptionEnable(password.getBytes())
            .make();

    /**
     * Create a Map / Get the existing map.
     */
    ctDB = db.getTreeMap("database");
}

/**
 * File existence check.
 * If file doesn't exists -> Create a new db file and inform the user.
 */
private static boolean isFileDatabaseOK() 
{       
    /**
     * If the file doesn't exists (First run) create a new file and 
     * inform the user.
     */
    if(!dbFile.exists())
    {
        try 
        {
            dbFile.getParentFile().mkdirs();
            dbFile.createNewFile();

            /**
             * TODO 
             * System.out.println("Database not found. Creating a new one.");
             */

            return true;
        }
        catch (IOException e)
        {
            /**
             * TODO Error handling
             */
            e.printStackTrace();
            return false;
        }
    }
    else
    {           
        return true;
    }
}

/**
 * Database methods / operations.
 */

/**
 * Get objects by id.
 * @param id    ->  Search parameter.
 * @return      ->  The object that belongs to the id.
 */
public String get(int id) 
{
    return ctDB.get(id);
}

/**
 * Adding objects to the database.
 * @param id -> The key reference to the object as 'id'.
 * @param object -> The object to cache.
 */
public void put(int id, String object)
{
    ctDB.put(id, object);

    db.commit();
}
}

:

 DBManager manager = DBManager.getInstance();
 manager.put(1, "test");
 Sytem.out.println(manger.get(1));

Answer 3

G1GC , .

-XX:MaxGCPauseMillis
-XX:G1HeapRegionSize
-XX:ParallelGCThreads
-XX:ConcGCThreads

Java.

:

Java 7 (JDK 7) G1

OutOfMemory, 20% ?

, mat, .

, . . , .