Hozy's Blogger

2007-08-24T12:28:00.000-07:00

Difference between Gantt and PERT charts?

A Gantt chart lists tasks in a project on a timeline with their interdependencies. It often also shows who is responsible for what task. It is especially useful for planning tasks in a project, and monitoring progress as the project goes on. Gantt charts emphasise time rather than task relationships.

A PERT chart, in comparison, looks more like a flow chart and concentrates on the relationships between tasks (especially their dependencies) and less on the timeline. PERT charts emphasise task relationships rather than time.

Both tools are commonly used, and they are often both used for the same project.

The PERT chart is sometimes preferred over the Gantt chart because it clearly illustrates task dependencies. On the other hand, the PERT chart can be much more difficult to interpret, especially on complex projects. Frequently, project managers use both techniques.

2007-08-24T12:10:00.000-07:00

What is OPatch?

OPatch is an Oracle supplied utility to applying interim patches to Oracle's software.

OPatch supports:

Applying an interim patch

Rolling back the application of an interim patch

Conflict resolution when applying an interim patch after previous interim patches have been applied

Reporting on installed products and Interim (One-Off) patch

2007-08-24T11:40:00.000-07:00

What is Oracle Interim (One-Off) Patches?

Oracle Interim Patch is a bug(s) fix made available to customers who for business reasons cannot wait until the next Patch Set or new product release to get a fix. Oracle may also recommend interim patches (such as security patches) to be applied to the systems. Interim patches can only be applied to a particular product version (base release or patch set). For example, an interim patch created for 8.1.7.3 should NOT be installed on 8.1.7.2 or 8.1.7.4. All Interim Patches are included in a future (usually next) Patch Set as well as the next product release.

2007-08-23T23:25:00.000-07:00

What is Virtualization?

It’s a technique of abstracting the underlying hardware to run multiple operating systems and multiple applications on the same computer at the same time.

There are two broad categories of virtualization:

* Platform virtualization – Example include Vmware, Xen
* Resource virtualization – Example include SAN, VPN, Partitioning

Three types of Virtualization implementations:

Full virtualization - the hypervisor provides a fully emulated machine in which an operating system can run. VMWare® is a good example. The biggest advantage to this approach is its flexibility: one could run a RISCbased OS as a guest on an Intel-based host. While this is an obvious approach, there are significant performance problems in trying to emulate a complete set of hardware in software. Even with painstaking optimization, it is very difficult to get useful performance from a fully virtualized environment.

Single Kernel Image (SKI) - At the other end of the spectrum is the Single Kernel Image (SKI), in which the host OS spawns additional copies of itself. This kind of virtualization can be found in Swsoft Virtuozzo and Sun® Solaris® Zones. SKI can be thought of as “lightweight” virtualization. While this approach avoids the performance problems with pure emulation, it does so at the expense of flexibility. It is not possible, for instance, to run different versions or even different patch levels of a particular operating system on the same machine. Whatever versions exist in the host, that same software will be provided in the guest. SKI also sacrifices the security and reliability provided by other virtualization methods. If the kernel is exploited, all OS instances resident on the system will be compromised.

Paravirtualization - found in the XenSource® open source Xen product, attempts to reconcile these two approaches. Instead of emulating hardware, paravirtualization uses slightly altered versions of the operating system which allows access to the hardware resources directly as managed by the hypervisor. This is known as hardware-assisted virtualization, and improves performance significantly. In order to retain flexibility, the guest OS is not tied to its host OS. Drastically different operating systems can be running in a hypervisor at the same time, just as they can under full virtualization. In this way, paravirtualization can be thought of as a low-overhead full virtualization.