For Java applications is difficult and expensive to achieve predictable, scalable performance. Simple switching from the single-server environments to multi-server can cause overall application throughput to collapse. Adding more data can cause the database to need progressively more resources. Java applications that work instantly in test, can be twenty times slower in response time when loaded with concurrent users.

The only (very complex) way to truly scale Java applications is to use three server tiers. The first is a HTTP-driven GUI, the second a Java server that de/serializes the tables of the third database tier into Java objects to perform the application logic. These tree tiers are often referred to as clustering, which is incorrect. Clustering is not related to vertically fragmenting the application but paralleling each server tier horizontally. So clustering can only be implemented independently for each of the tiers and requires very different functionality in each. In the case of the Web tier, no server-to-server communication is necessary, whereas at the other extreme, the database tier must manage transactional consistency across its cluster. This means that the cost of scalability is dramatically different for each of those tiers. Management and tuning is also completely different for each as well.

The HTTP tier performs SSL encryption and decryption duties, handles unique client connections by means of HTTP headers with ‘sticky load balancing’ information. HTTP requests are load-balanced across stateless servers and routed to designated J2EE server for processing. The application has to support sticky load balancing from the Web tier to be able to cluster both HTTP and Java tiers. Such Java applications exhibit intra-tier communication complexity that directly impairs scalable performance. The clustering of the database server has to be a function of the database product used, but it is impossible to scale the Java server without implementing some form of local data caching. Common forms are coherent clustered caching, fully replicated caching and partitioned caching.

Clustered caching maintains data in the Java application tier to satisfy data access requests from the cache without loading the database. The cache must not grow too large and provide data as current as necessary. Not all data is needed up-to-date. The cache expires data by LRU – least recently used and elapsed time algorithms.  In clustered systems, servers notify each other about data modifications and either delete or refresh the outdated data page. Coherent clustered caching needs the same as application logic to synchronize cache pages to guarantee a thread-safe implementation. A kind of dual-phase commit on page changes is required in a distributed cache to maintain transactional data consistency.

A fully replicated cache however does not have the problems of clustered caching but shares modifications with other members of the cluster in a “push” model.  While the data access has no measurable latency, a transaction should only be closed when the data from the cache has been serialized to the database tier. This is however mostly done in lazy writes and thus risky. The other problem is related to data locking because theoretically two servers can access the same data to write at the same time and therefore cause conflicts at transaction close.

The solution is the partitioned cache where each cluster server owns one unique fragment of the complete data set. All data are cached to the other servers but writes have to be synchronized to the owning server, but because communication is any-to-any, partitioned caches scale linearly with number of requests and data volume as you add servers. Replicating data from the owner and de-serializing tables into objects adds substantial latency. Therefore the application servers typically ‘object-cache the database-cache’ to avoid the additional de-serialization overhead for multiple object requests. The cache can load many objects from a single cache page in one I/O request rather than reading multiple table entries.

However, a substantially growing number of applications no longer read data from a database. Particularly process oriented applications (and that should be all of them) require data synchronization via backend interfaces such as SOA or MQ series from application silos. More often than not such interfaces require stateful conversations. Compared to database access, Web services based communications are at least a magnitude worse in performance, response time and throughput. Much of that has to do with the problems of XML defined data structures, the weak, ambiguous, and non-canonical XSD-based data definitions and the resultant parsing and validation. To reduce the number of transfers, SOA requests often pass a lot of incidental data because it might be needed, to avoid multiple data accesses. Obviously that is similar to creating a kind of SOA cache, but without any of the above mentioned mechanisms of data concurrency. Web services provided data are in principle always out of date. Web services transactions are so slow that they can not be used for applications that involve user interactions but just for straight-through processes without user intervention. To implement clustered caching for SOA Web services creates substantial problems, mostly because there is no defined mechanism for push-updates and lazy database writes. All of it has to be manually implemented by the Java programmers and is mostly hard-coded and application specific.

The complexity of measuring and predicting hardware and software performance becomes therefore a very complex task. During my years in IBM one of the key elements of designing a well working mainframe environment was based on the balanced system approach. The right mix of CPU power, RAM, disk I/Os was needed to get the most bang for your buck. Today the need for network bandwidth for the various intricacies of each of the tiers becomes the key element while HW is looked at as a cheap commodity. The immense OVERHEAD involved in juggling Web/HTTP clusters, Java tier clusters and expensive High-Availability clusters for the database tier requires huge amounts of commodity HW that is mostly not balanced to achieve scalable applications. Most systems just provide enough of everything to work. The idea of Cloud computing has to do with providing virtualized resources to such tiered systems adding more overhead for the virtualization. Hm, it sounds not very professional and well thought out to me …

CONCLUSION: Could the substantial overhead in using sticky-load-balancing, transaction-safe Java caching and database clustering, plus the substantial overhead for parsing and validating the XML data for SOA not be avoided? All of the above have been reasons why I chose a different route for the Papyrus Platform. Rather than the immense complexity of multi-layered caches – with multiple conversion from tables to cache pages to objects and reverse – I decided to collapse the horizontal structures and work with a purely (vertical) object model from definition to storage. That enables the use of the meta-data repository for application life-cycle management and substantially simplifies systems management and tuning.

The proxy replication mechanism of the object-relational database of the Papyrus Platform uses a partitioned caching concept where there is always a unique data owner and each server node uses a replicated copy that is either pull or push updated as per proxy definition. The objects do not have to be de/serialized as they are cached/replicated/binary stored as is. The same mechanism works transparently for all objects that are populated via Web services or other backend interfaces. The drawback is that during testing or at low load it seems to be not as fast as a Java app, but in difference it does scale linearly without needing additional programming or software as you add more commodity HW. Papyrus uses the same concepts across all servers because there are no tiers necessary and it also does not need virtualization.

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Host based processing is not true client/server computing. Rather, host based processing refers to the traditional main frame environment in which all or virtually all of the processing is done on a central host. Often the user interface is through a dub terminal. Even if the user is employing a micro computer, the user`s station is generally limited to the role of a terminal emulator.

The most basic class of client/server configuration is one in which the server is principally responsible for providing a graphical user interface, whereas virtually all of the processing is done on the server. This configuration is typical of early client/server efforts, especially departmental-level systems. The rationale behind such configurations is that the user workstation is best suited to provide a user-friendly interface and those databases and applications can easily be maintained on central systems. Although the user gains the advantage of a better interface, this type of configuration does not generally lend itself to any significant gains in productivity or to any fundamental changes in the actual business functions that the system supports.

At the other extreme, virtually all application processing may be done at the client, with the exception of data validation routines and other database logic functions that are best performed at the server. Sophisticated database logic functions are housed on the client side. This architecture is perhaps the most common server/client approach in current use. It enables the user to employ applications tailored to local needs.

In a cooperative processing configuration, the application processing is performed in an optimized fashion by taking advantage of the strengths of both client and server machines and of the distribution of data. Such a configuration is more complex to set up and maintain. This type of configuration may offer greater user productivity gains and greater network efficiency that other client/server approaches.

The exact distribution of data and application processing will depend on the nature of the database information, the types of applications supported, the availability of interoperable vendor equipment, and the usage patterns within an organization.

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Server applications are useful if you want to upload or download files from client server.

The Bearshare peer-to-peer software applications promises the same as other programs produced out of the GNU/Gnutella stable. It offers the promise of free musical downloads. It is a bit harder to get a “free download” of the basic Bearshare program than others, such as Limewire and Frostwire. It promises a surprise you won’t like or appreciate; more details follow in a later paragraph. Limewire was eventually obtained from a freeware website on the internet and Frostwire was acquired from the Limewire quite easily.

But I am going to talk about Bearshare in this article. This is my experience: When I went to Bearshare they offered a membership in addition to the basic Bearshare software. I downloaded the software and attempted to install it. The following experience represents a danger still present upon the internet and especially with peer-to-peer applications.

Upon installing the Bearshare basic software package my antivirus application went crazy! It identified two unwanted passengers, an adware robot plus another which was a Startup Registry. These were indeed unpleasant and unexpected. I was very trusting of the website, which turned out to be a terrible mistake of mine. It had all the correct “looks” of a GNU open source website which I allowed to influence me.

This caught me totally unaware when my system’s protection stepped in to prevent a possible dangerous event. I now feel that Bearshare and possibly other peer-to-peer sharing software applications may have “Trojans” and other nasties embedded. Using my “leftist” brain I found that I was suspicious of the intentions of say the Record Industry Association of America.

What if they were unsatisfied with the impact of their lawsuit against individuals and Napster; maybe setting up pseudo free websites with contaminated software applications, the purpose of which is to scare people off from sharing files, software, audio, and video. I know what I’m writing is totally improvable; it sounds as preposterous as claiming that sharing files on the internet can harmfully reduce musical CD sales.

I wonder who would believe that? Anyway, there won’t be any free music downloads using Bearshare to my computer. The surprises it gave me outweigh any promise of no monthly charges.

Major online music stores like HMV, Amazon and so on carry many labels and their selection is fantastic with loads of music pieces, movie soundtracks, songs, music videos and practically unlimited music downloads are available for you to download. Never worry about where to download music again. However, music lovers after getting the thrill of downloading lots of music files start to feel the pinch. This is where the latest new generation of music download sites would make them scream with excitement again.

You see, the new music download sites offer unlimited music downloads. And by that, it means that you not only can find any title or album you want but also download them without any quantity restriction. Be it 1000 songs or 10,000 songs that you intend to download, it does not matter. These music download sites would charge you only once for unlimited music downloads at an affordable rate that even teens have the ability to get their memberships. That is the whole intention of the music download sites, to reach the mass musical audience.

But there are almost a dozen of unlimited music downloads sites that solve your problem of where to download music quickly. So it can be quite a challenge to decide which to go for. Do not worry as here are some useful tips to help you along to decide where to download music from which music download sites for unlimited music downloads. These would find you the suitable music download site.

Be sure to first check out the music selection of these music download sites. There is really no point in using them even if they have millions of music pieces and songs, ie unlimited music downloads in their collection but none are what you want. Most should carry the general range of music that are more common like pop, rock and so on. But if you are looking for specific niche genres which are a little bit uncommon, you need to check if the music collection at these music download sites carries your desired label or brand of music.

Secondly, you need to confirm the file format of the music files you are downloading from the music download sites. This is easy as many have unlimited music downloads in MP3 format. This is the most commonly readable format used by most MP3 players or digital portable players. So as long as the music download site has it, you know this is where to download music so that you can enjoy unlimited music downloads on your player.

Another thing to take note of is some music download sites for unlimited music downloads require you to download special client application in order to download music online. If you are a frequent traveller, you may not like the idea that you need to install software on your computer in order to download music. This means that you can only do so from home. As such, you may want to go for those that do not require any client applications to do so. That said, the client application does not need a lot of computer resources and can be easily installed and removed. It is really your choice when getting the unlimited music downloads from the music download sites.

Anyone who wishes to learn more about where to download music at amazingly low one-off prices can visit my music blog and begin your journey of putting unlimited music downloads on your computer or MP3 player.

1. Check your PC.

Before you download Vista Windows, check your computer if it’s ready for upgrades. To do this, you need to download and run the Windows Upgrade Advisor tool. This will assess your computer and give you a list of the Vista versions that are compatible with your unit. To be able to download Vista Windows, your computer must have at least 800MHz. Premium-ready PCs need at least 1GHz.

2. Make sure you have enough memory and hard drive space.

Another thing to note before you download Vista Windows your PC must have at least 512 MB of RAM. The minimum requirement for a premium-ready PC is 1 GB of system RAM. Plus, to be able to download Vista Windows, your hard drive size and free space must be no less than 40 GB and 15 GB, respectively.

3. Determine graphics adapter capability.

To enable you to download Vista Windows, your graphics adapter must be DirectX 9 capable. Premium-ready machines need at least 128 MB of video RAM to be able to download Vista Windows. Cards that are Vista-capable should have a minimum 64 MB of video RAM. These requirements need to be met if you plan to exploit the Aero Glass graphics. Otherwise, if your existing video adapter is Vista-capable, there is no need to upgrade it. It should be noted that a notebook computer with graphics card that is not compatible has a lesser chance of a successful upgrade to the new system.

4. Your computer must have a DVD drive.

So you can download Vista Windows, your PC should have a DVD drive in which you could install Vista.

5. Determine the version of Vista your computer is capable of running.

Before you download Vista Windows, determine first the version most appropriate for your computer. The five different editions are:

· Windows Vista Home Basic – provides basic operating system usability; suitable for average home users; will sell for $200 for new PCs, and $100 as an upgrade for those with existing Windows license

· Windows Vista Home Premium – offers more functionality than previous Vista Home Basic version; best choice for most PC users; features Aero and Media Center interface, DVD Maker, Movie Maker HD, backup scheduler, SideShow that allows use of auxiliary displays, comes with a Sync Center to synchronize files with other PCs over a home network, and parental controls; premium costs $240 for new computers and P160 as an upgrade if you have an existing Windows XP Home license

· Windows Vista Business – useful for standard business needs; comparable to Windows XP Professional; will be a staple on the corporate desktop.

· Windows Vista Enterprise – has advanced features like BitLocker Drive Encryption for laptops, application compatibility tools, and multi-language support

· Windows Vista Ultimate – has all the features of Vista Home Premium; features support for dual CPUs (multi-core are supported in lower versions), remote desktop host, file encryption (with full-drive BitLocker capability), faxing, domain-based networking for office networks, and web hosting; will sell for $400 for new PCs and $260 as an upgrade if you have an existing Windows XP Home or Pro license.

6. Existing applications must be capable of running under Vista.

To ensure that you can download Vista Windows and install it successfully, run the Application Compatibility Toolkit to help you distinguish the applications that may not be operate under Vista.

7. Back up your data.

Before you download Vista Windows, do not forget to back up your data. Prior to installation of the new operating system, be sure to check that you have all the installation media from your existing software and the proper licensing information.

The steps above are all essential requirements that you need to consider before you download Vista Windows. Also, notebook computers and desktop PCs should be able to meet all the hardware specifications.