Bug 180189 Support in memory data set cache.
Currently, Design-Time Data Cache is stored on disks. By performance tests using ramdisk, we found that caching in physical memory can improve the performance of RunAndRender by 30%.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/executor/DataSetCacheManager.java
alwaysCacheRowCount = 0;
		cacheMapManager = new CacheMapManager( tempDir );
		this.dataEngine = dataEngine;
		needToMerge = true;
	}
	/**
	 * Enable cache on data set
	 * 
	 * @param cacheOption
	 */
	public void setCacheOption( int cacheOption )
	{
		this.cacheOption = cacheOption;
	}
	/**
	 * @return
	 */
	public int suspendCache( )
	{
		int lastCacheOption = this.cacheOption;
		this.setCacheOption( DataEngineContext.CACHE_USE_DISABLE );
		return lastCacheOption;
	}
	/**
	 * @param rowCount
	 */
	public void setAlwaysCacheRowCount( int rowCount )
	{
		this.alwaysCacheRowCount = rowCount;
	}