HSQLDB example source code file (Cache.java)

This example HSQLDB source code file (Cache.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - HSQLDB tags/keywords

cache, cachedobject, cachedobject, cachedobjectcomparator, cachedobjectcomparator, compare_position, compare_size, datafilecache, io, ioexception, ioexception, object, objectcachehashmap, stopwatch, stopwatch

The HSQLDB Cache.java source code

/* Copyright (c) 2001-2008, The HSQL Development Group
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.hsqldb.persist;

import java.io.IOException;

import org.hsqldb.Trace;
import org.hsqldb.lib.Iterator;
import org.hsqldb.lib.ObjectComparator;
import org.hsqldb.lib.Sort;
import org.hsqldb.lib.StopWatch;
import org.hsqldb.store.ObjectCacheHashMap;

/**
 * New implementation of row caching for CACHED tables.<p>
 *
 * Manages memory for the cache map and its contents based on least recently
 * used clearup.<p>
 * Also provides services for selecting rows to be saved and passing them
 * to DataFileCache.<p>
 *
 * @author fredt@users
 * @version 1.8.0
 */
public class Cache {

    final DataFileCache                  dataFileCache;
    private int                          capacity;         // number of Rows
    private long                         bytesCapacity;    // number of bytes
    private final CachedObjectComparator rowComparator;

//
    private CachedObject[] rowTable;

//
    private final ObjectCacheHashMap cacheMap;
    long                             cacheBytesLength;

    // for testing
    StopWatch saveAllTimer = new StopWatch(false);
    StopWatch makeRowTimer = new StopWatch(false);
    StopWatch sortTimer    = new StopWatch(false);
    int       makeRowCount = 0;
    int       saveRowCount = 0;

    Cache(DataFileCache dfc) {

        dataFileCache    = dfc;
        capacity         = dfc.capacity();
        bytesCapacity    = dfc.bytesCapacity();
        rowComparator    = new CachedObjectComparator();
        rowTable         = new CachedObject[capacity];
        cacheMap         = new ObjectCacheHashMap(capacity);
        cacheBytesLength = 0;
    }

    /**
     *  Structural initialisations take place here. This allows the Cache to
     *  be resized while the database is in operation.
     */
    void init(int capacity, long bytesCapacity) {}

    int size() {
        return cacheMap.size();
    }

    long getTotalCachedBlockSize() {
        return cacheBytesLength;
    }

    /**
     * Returns a row if in memory cache.
     */
    synchronized CachedObject get(int pos) {
        return (CachedObject) cacheMap.get(pos);
    }

    /**
     * Adds a row to the cache.
     */
    synchronized void put(int key,
                                 CachedObject row) throws IOException {

        int storageSize = row.getStorageSize();

        if (cacheMap.size() >= capacity
                || storageSize + cacheBytesLength > bytesCapacity) {
            cleanUp();
        }

        cacheMap.put(key, row);

        cacheBytesLength += storageSize;
    }

    /**
     * Removes an object from memory cache. Does not release the file storage.
     */
    synchronized CachedObject release(int i) {

        CachedObject r = (CachedObject) cacheMap.remove(i);

        if (r == null) {
            return null;
        }

        cacheBytesLength -= r.getStorageSize();

        return r;
    }

    /**
     * Reduces the number of rows held in this Cache object. <p>
     *
     * Cleanup is done by checking the accessCount of the Rows and removing
     * the rows with the lowest access count.
     *
     * Index operations require that up to 5 recently accessed rows remain
     * in the cache.
     *
     */
    private synchronized void cleanUp() throws IOException {

        int removeCount = cacheMap.size() / 2;
        int accessTarget = cacheMap.getAccessCountCeiling(removeCount,
            removeCount / 8);
        ObjectCacheHashMap.ObjectCacheIterator it = cacheMap.iterator();
        int                                    savecount = 0;

        for (; it.hasNext(); ) {
            CachedObject r = (CachedObject) it.next();

            if (it.getAccessCount() <= accessTarget) {
                if (!r.isKeepInMemory()) {
                    if (r.hasChanged()) {
                        rowTable[savecount++] = r;
                    }

                    it.remove();

                    cacheBytesLength -= r.getStorageSize();
                }
            }
        }

        cacheMap.setAccessCountFloor(accessTarget);
        saveRows(savecount);
    }

    private synchronized void saveRows(int count) throws IOException {

        if (count == 0) {
            return;
        }

        rowComparator.setType(rowComparator.COMPARE_POSITION);
        sortTimer.start();
        Sort.sort(rowTable, rowComparator, 0, count - 1);
        sortTimer.stop();
        saveAllTimer.start();
        dataFileCache.saveRows(rowTable, 0, count);

        saveRowCount += count;

        /*
                // not necessary if the full storage size of each object is written out
                try {
                    dataFile.file.seek(fileFreePosition);
                } catch (IOException e){}
        */
        saveAllTimer.stop();
    }

    /**
     * Writes out all modified cached Rows.
     */
    synchronized void saveAll() throws IOException {

        Iterator it        = cacheMap.iterator();
        int      savecount = 0;

        for (; it.hasNext(); ) {
            CachedObject r = (CachedObject) it.next();

            if (r.hasChanged()) {
                rowTable[savecount++] = r;
            }
        }

        saveRows(savecount);
        Trace.printSystemOut(
            saveAllTimer.elapsedTimeToMessage(
                "Cache.saveRow() total row save time"));
        Trace.printSystemOut("Cache.saveRow() total row save count = "
                             + saveRowCount);
        Trace.printSystemOut(
            makeRowTimer.elapsedTimeToMessage(
                "Cache.makeRow() total row load time"));
        Trace.printSystemOut("Cache.makeRow() total row load count = "
                             + makeRowCount);
        Trace.printSystemOut(
            sortTimer.elapsedTimeToMessage("Cache.sort() total time"));
    }

    /**
     * clears out the memory cache
     */
    synchronized void clear() {

        cacheMap.clear();

        cacheBytesLength = 0;
    }

    static class CachedObjectComparator implements ObjectComparator {

        static final int COMPARE_LAST_ACCESS = 0;
        static final int COMPARE_POSITION    = 1;
        static final int COMPARE_SIZE        = 2;
        private int      compareType;

        CachedObjectComparator() {}

        void setType(int type) {
            compareType = type;
        }

        public int compare(Object a, Object b) {

            switch (compareType) {

                case COMPARE_POSITION :
                    return ((CachedObject) a).getPos()
                           - ((CachedObject) b).getPos();

                case COMPARE_SIZE :
                    return ((CachedObject) a).getStorageSize()
                           - ((CachedObject) b).getStorageSize();

                default :
                    return 0;
            }
        }
    }
}