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/*
 * Copyright (c) 2002-2016 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.pagecache;

import org.neo4j.kernel.impl.util.OsBeanUtil;
import org.neo4j.helpers.Service;
import org.neo4j.io.ByteUnit;
import org.neo4j.io.fs.FileSystemAbstraction;
import org.neo4j.io.pagecache.PageCache;
import org.neo4j.io.pagecache.PageSwapperFactory;
import org.neo4j.io.pagecache.impl.SingleFilePageSwapperFactory;
import org.neo4j.io.pagecache.impl.muninn.MuninnPageCache;
import org.neo4j.io.pagecache.tracing.PageCacheTracer;
import org.neo4j.kernel.configuration.Config;
import org.neo4j.logging.Log;

import static org.neo4j.graphdb.factory.GraphDatabaseSettings.mapped_memory_page_size;
import static org.neo4j.graphdb.factory.GraphDatabaseSettings.pagecache_memory;
import static org.neo4j.graphdb.factory.GraphDatabaseSettings.pagecache_swapper;

public class ConfiguringPageCacheFactory
{
    private final PageSwapperFactory swapperFactory;
    private final Config config;
    private final PageCacheTracer tracer;
    private final Log log;
    private PageCache pageCache;

    public ConfiguringPageCacheFactory(
            FileSystemAbstraction fs, Config config, PageCacheTracer tracer, Log log )
    {
        this.swapperFactory = createAndConfigureSwapperFactory( fs, config );
        this.config = config;
        this.tracer = tracer;
        this.log = log;
    }

    private PageSwapperFactory createAndConfigureSwapperFactory( FileSystemAbstraction fs, Config config )
    {
        String desiredImplementation = config.get( pagecache_swapper );

        if ( desiredImplementation != null )
        {
            for ( PageSwapperFactory factory : Service.load( PageSwapperFactory.class ) )
            {
                if ( factory.implementationName().equals( desiredImplementation ) )
                {
                    factory.setFileSystemAbstraction( fs );
                    if ( factory instanceof ConfigurablePageSwapperFactory )
                    {
                        ConfigurablePageSwapperFactory configurableFactory = (ConfigurablePageSwapperFactory) factory;
                        configurableFactory.configure( config );
                    }
                    return factory;
                }
            }
        }

        SingleFilePageSwapperFactory factory = new SingleFilePageSwapperFactory();
        factory.setFileSystemAbstraction( fs );
        return factory;
    }

    public synchronized PageCache getOrCreatePageCache()
    {
        if ( pageCache == null )
        {
            pageCache = createPageCache();
        }
        return pageCache;
    }

    protected PageCache createPageCache()
    {
        int cachePageSize = calculatePageSize( config, swapperFactory );
        int maxPages = calculateMaxPages( config, cachePageSize );
        return new MuninnPageCache(
                swapperFactory,
                maxPages,
                cachePageSize,
                tracer );
    }

    public int calculateMaxPages( Config config, int cachePageSize )
    {
        long pageCacheMemory = config.get( pagecache_memory );
        long maxHeap = Runtime.getRuntime().maxMemory();
        if ( pageCacheMemory / maxHeap > 100 )
        {
            log.warn( "The memory configuration looks unbalanced. It is generally recommended to have at least " +
                      "10 KiB of heap memory, for every 1 MiB of page cache memory. The current configuration is " +
                      "allocating %s bytes for the page cache, and %s bytes for the heap.", pageCacheMemory, maxHeap );
        }
        long pageCount = pageCacheMemory / cachePageSize;
        return (int) Math.min( Integer.MAX_VALUE - 2000, pageCount );
    }

    public int calculatePageSize( Config config, PageSwapperFactory swapperFactory )
    {
        int pageSwappersPageSizeHint = swapperFactory.getCachePageSizeHint();
        int configuredPageSize = config.get( mapped_memory_page_size ).intValue();
        if ( configuredPageSize == 0 || swapperFactory.isCachePageSizeHintStrict() )
        {
            return pageSwappersPageSizeHint;
        }
        return configuredPageSize;
    }

    public void dumpConfiguration()
    {
        int cachePageSize = calculatePageSize( config, swapperFactory );
        long maxPages = calculateMaxPages( config, cachePageSize );
        long totalPhysicalMemory = OsBeanUtil.getTotalPhysicalMemory();
        String totalPhysicalMemMb = (totalPhysicalMemory == OsBeanUtil.VALUE_UNAVAILABLE)
                                    ? "?" : "" + ByteUnit.Byte.toMebiBytes( totalPhysicalMemory );
        long maxVmUsageMb = ByteUnit.Byte.toMebiBytes( Runtime.getRuntime().maxMemory() );
        long pageCacheMb = ByteUnit.Byte.toMebiBytes(maxPages * cachePageSize);
        String msg = "Physical mem: " + totalPhysicalMemMb + " MiB," +
                     " Heap size: " + maxVmUsageMb + " MiB," +
                     " Page cache size: " + pageCacheMb + " MiB.";

        log.info( msg );
    }
}