This chapter provides an introduction to capacity planning. Capacity planning is the process of determining what type of hardware and software configuration is required to meet application needs adequately. Capacity planning is not an exact science. Every application is different and every user behavior is different.
A number of factors influence how much capacity a given hardware configuration will need in order to support a WebLogic Server instance and a given application. The hardware capacity required to support your application depends on the specifics of the application and configuration. You should consider how each of these factors applies to your configuration and application.
The following sections discuss several of these factors. Understanding these factors and considering the requirements of your application will aid you in generating server hardware requirements for your configuration. Consider the capacity planning questions in Table B-1.
|Capacity Planning Questions||For Information, See:|
Is WebLogic Server well-tuned?
How well-designed is the user application?
Is there enough bandwidth?
How many transactions need to run simultaneously?
Is the database a limiting factor? Are there additional user storage requirements?
What is running on the machine in addition to WebLogic Server?
Do clients use SSL to connect to WebLogic Server?
What types of traffic do the clients generate?
What types of clients connect to the WebLogic Server application?
Is your deployment configured for a cluster?
Are your servers configured for migration?
Primarily, two types of clients can connect to WebLogic Server:
Web-based clients, such as Web browsers and HTTP proxies, use the HTTP or HTTPS (secure) protocol to obtain HTML or servlet output.
Programmatic clients, such as Java applications and applets, can connect through the T3 protocol and use RMI to connect to the server.
The stateless nature of HTTP requires that the server handle more overhead than is the case with programmatic clients. However, the benefits of HTTP clients are numerous, such as the availability of browsers and firewall compatibility, and are usually worth the performance costs.
Programmatic clients are generally more efficient than HTTP clients because T3 does more of the presentation work on the client side. Programmatic clients typically call directly into EJBs while Web clients usually go through servlets. This eliminates the work the server must do for presentation. The T3 protocol operates using sockets and has a long-standing connection to the server.
A WebLogic Server installation that relies only on programmatic clients should be able to handle more concurrent clients than an HTTP proxy that is serving installations. If you are tunneling T3 over HTTP, you should not expect this performance benefit. In fact, performance of T3 over HTTP is generally 15 percent worse than typical HTTP and similarly reduces the optimum capacity of your WebLogic Server installation.
What types of server traffic do the clients generate? If you are using T3 clients, most interaction with the server involves Remote Method Invocation (RMI.) Clients using RMI do not generate heavy traffic to the server because there is only one sender and one listener.
RMI can use HTTP tunneling to allow RMI calls to traverse a firewall. RMI tunneled through HTTP often does not deliver the higher degree of performance provided by non-tunneled RMI.
Secure sockets layer (SSL) is a standard for secure Internet communications. WebLogic Server security services support X.509 digital certificates and access control lists (ACLs) to authenticate participants and manage access to network services. For example, SSL can protect JSP pages listing employee salaries, blocking access to confidential information.
SSL involves intensive computing operations. When supporting the cryptography operations in the SSL protocol, WebLogic Server can not handle as many simultaneous connections.
The number of SSL connections required out of the total number of clients required. Typically, for every SSL connection that the server can handle, it can handle three non-SSL connections. SSL substantially reduces the capacity of the server depending upon the strength of encryption used in the SSL connections. Also, the amount of overhead SSL imposes is related to how many client interactions have SSL enabled. WebLogic Server includes native performance packs for SSL operations.
What is running on the machine in addition to a WebLogic Server? The machine may be processing much more than presentation and business logic. For example, it could be running a Web server or maintaining a remote information feed, such as a stock information feed from a quote service.
Consider how much of your WebLogic Server machine's processing power is consumed by processes unrelated to WebLogic Server. In the case in which WebLogic Server (or the machine on which it resides) is doing substantial additional work, you need to determine how much processing power will be drained by other processes. When a Web server proxy is running on the same machine as WebLogic Server, expect anywhere from 25 to 50 percent of the computing capacity.
Is the database a bottleneck? Are there additional user storage requirements? Often the database server runs out of capacity much sooner that WebLogic Server does. Plan for a database that is sufficiently robust to handle the application. Typically, a good application's database requires hardware three to four times more powerful than the application server hardware. It is good practice to use a separate machine for your database server.
Generally, you can tell if your database is the bottleneck if you are unable to maintain WebLogic Server CPU usage in the 85 to 95 percent range. This indicates that WebLogic Server is often idle and waiting for the database to return results. With load balancing in a cluster, the CPU utilization across the nodes should be about even.
Some database vendors are beginning to provide capacity planning information for application servers. Frequently this is a response to the three-tier model for applications.
An application might require user storage for operations that do not interact with a database. For example, in a secure system disk and memory are required to store security information for each user. You should calculate the size required to store one user's information, and multiply by the maximum number of expected users.
How many transactions must run concurrently? Determine the maximum number of concurrent sessions WebLogic Server will be called upon to handle. For each session, you will need to add more RAM for efficiency. Oracle recommends that you install a minimum of 256 MB of memory for each WebLogic Server installation that will be handling more than minimal capacity.
Next, research the maximum number of clients that will make requests at the same time, and how frequently each client will be making a request. The number of user interactions per second with WebLogic Server represents the total number of interactions that should be handled per second by a given WebLogic Server deployment. Typically for Web deployments, user interactions access JSP pages or servlets. User interactions in application deployments typically access EJBs.
Consider also the maximum number of transactions in a given period to handle spikes in demand. For example, in a stock report application, plan for a surge after the stock market opens and before it closes. If your company is broadcasting a Web site as part of an advertisement during the World Series or World Cup Soccer playoffs, you should expect spikes in demand.
Is the bandwidth sufficient? WebLogic Server requires enough bandwidth to handle all connections from clients. In the case of programmatic clients, each client JVM will have a single socket to the server. Each socket requires bandwidth. A WebLogic Server handling programmatic clients should have 125 to 150 percent the bandwidth that a server with Web-based clients would handle. If you are interested in the bandwidth required to run a web server, you can assume that each 56kbps (kilobits per second) of bandwidth can handle between seven and ten simultaneous requests depending upon the size of the content that you are delivering. If you are handling only HTTP clients, expect a similar bandwidth requirement as a Web server serving static pages.
The primary factor affecting the requirements for a LAN infrastructure is the use of replicated sessions for servlets and stateful session EJBs. In a cluster, replicated sessions are the biggest consumer of LAN bandwidth. Consider whether your application will require the replication of session information for servlets and EJBs.
To determine whether you have enough bandwidth in a given deployment, look at the network tools provided by your network operating system vendor. In most cases, including Windows NT, Windows 2000, and Solaris, you can inspect the load on the network system. If the load is very high, bandwidth may be a bottleneck for your system.
Clusters greatly improve efficiency and failover. Customers using clustering should not see any noticeable performance degradation. A number of WebLogic Server deployments in production involve placing a cluster of WebLogic Server instances on a single multiprocessor server.
Large clusters performing replicated sessions for Enterprise JavaBeans (EJBs) or servlets require more bandwidth than smaller clusters. Consider the size of session data and the size of the cluster.
Are your servers configured for migration? Migration in WebLogic Server is the process of moving a clustered WebLogic Server instance or a component running on a clustered instance elsewhere in the event of failure. In the case of whole server migration, the server instance is migrated to a different physical machine upon failure, either manually or automatically.
For capacity planning in a production environment, keep in mind that server startup during migration taxes CPU utilization. You cannot assume that because a machine can handle x number of servers running concurrently that it also can handle that same number of servers starting up on the same machine at the same time.
How well-designed is the application? WebLogic Server is a platform for user applications. Badly designed or unoptimized user applications can drastically slow down the performance of a given configuration from 10 to 50 percent. The prudent course is to assume that every application that is developed for WebLogic Server will not be optimal and will not perform as well as benchmark applications. Increase the maximum capacity that you calculate or expect. See Tune Your Application.
At this stage in capacity planning, you gather information about the level of activity expected on your server, the anticipated number of users, the number of requests, acceptable response time, and preferred hardware configuration. Capacity planning for server hardware should focus on maximum performance requirements and set measurable objectives for capacity.
The numbers that you calculate from using one of our sample applications are of course just a rough approximation of what you may see with your application. There is no substitute for benchmarking with the actual production application using production hardware. In particular, your application may reveal subtle contention or other issues not captured by our test applications.
When you examine performance, a number of factors influence how much capacity a given hardware configuration will need in order to support WebLogic Server and a given application. The hardware capacity required to support your application depends on the specifics of the application and configuration. You should consider how each factor applies to your configuration and application.
The Standard Performance Evaluation Corporation, at
http://www.spec.org, provides a set of standardized benchmarks and metrics for evaluating computer system performance.
See "Supported Configurations" in What's New in Oracle WebLogic Server for links to the latest certification information on the hardware/operating system platforms that are supported for each release of WebLogic Server.
Network performance is affected when the supply of resources is unable to keep up with the demand for resources. Today's enterprise-level networks are very fast and are now rarely the direct cause of performance in well-designed applications. However, if you find that you have a problem with one or more network components (hardware or software), work with your network administrator to isolate and eliminate the problem. You should also verify that you have an appropriate amount of network bandwidth available for WebLogic Server and the connections it makes to other tiers in your architecture, such as client and database connections. Therefore, it is important to continually monitor your network performance to troubleshoot potential performance bottlenecks.
A common definition of bandwidth is "the rate of the data communications transmission, usually measured in bits-per-second, which is the capacity of the link to send and receive communications." A machine running WebLogic Server requires enough network bandwidth to handle all WebLogic Server client connections. In the case of programmatic clients, each client JVM has a single socket to the server, and each socket requires dedicated bandwidth. A WebLogic Server instance handling programmatic clients should have 125–150 percent of the bandwidth that a similar Web server would handle. If you are handling only HTTP clients, expect a bandwidth requirement similar to a Web server serving static pages.
To determine whether you have enough bandwidth in a given deployment, you can use the network monitoring tools provided by your network operating system vendor to see what the load is on the network system. You can also use common operating system tools, such as the
netstat command for Solaris or the System Monitor (
perfmon) for Windows, to monitor your network utilization. If the load is very high, bandwidth may be a bottleneck for your system.
Also monitor the amount of data being transferred across the your network by checking the data transferred between the application and the application server, and between the application server and the database server. This amount should not exceed your network bandwidth; otherwise, your network becomes the bottleneck. To verify this, monitor the network statistics for retransmission and duplicate packets, as follows:
netstat -s -P tcp
The Oracle Technology Network provides detailed documentation for WebLogic Server. See
Information on topics related to capacity planning is available from numerous third-party software sources.