The Essentials Of Database High Availability

Sites classified as highly available are designed to be ultra-resilient and offer the best protection from single failure points and underlying platform errors. The umbrella of availability incorporates failure, recovery and site resilience. Availability is commonly measured based on the time percentage that any system is working and active.

In order to improve availability it is necessary to put in place comprehensively engineered solutions. Since prediction of when or how a system will fail is notoriously difficult to predict, the best method of planning improved reliability is to engender shorter recovery times. If a given system is able to recover from a failure within 86.4 seconds then it’s possible to have a failure on a daily basis and still provide an availability of 99.9% to users.

Recognizing Common Oracle Database Performance Issues

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Oracle database performance improvements require continual and iterative efforts to produce results. It is not a one and done activity. Constant vigilance and performance monitoring are required for long-term success.

Neither is it a matter of finding and removing one performance bottleneck. There are likely more than one to be found. In fact, further investigation may lead a DBA to an even greater performance problem.

Oracle database performance problems typically result from lack of data throughput, unacceptable user or job response time, or both. To determine the nature of the problem and create a path to resolution, you must gather as much performance data as possible, including from end users, call centers, or any other stakeholder who can speak to end user system performance.

The next step is to gather Oracle database performance statistics. This can be done using the Automatic Workload Repository (AWR) or with third-party solutions such as Confio Ignite for Oracle. The statistics captured by these tools include:

• Time model statistics
• Wait events
• Session and system statistics
• Active session history
• High-load SQL statistics

 

Common Oracle Database Performance Issues Defined

Using the above statistics will assist DBAs with finding some of the most common Oracle database performance problems. Here are a few:

• CPU Bottlenecks
  When the CPU approaches or exceeds maximum utilization performance problems begin. What is causing the CPU performance issues? Bad queries? Too many consecutive users? Solving CPU issues can greatly improve performance.
• I/O Capacity Issues
  Lack of I/O subsystem performance can translate to poor end-user performance. Increasing I/O capacity or decreasing I/O loads can assist in disk I/O utilization.
• Concurrency Issues
  Concurrent activities can lead to contention for shared resources that result in locks or waits for buffer cache. Monitoring session data can show DBAs where locks and waits are occurring while users wait for their request to be processed. Reducing or eliminating these with more efficient queries and database structures creates measurable performance improvements.
• Database Configuration Issues
  What configuration issues may be contributing to poor performance. Likely candidates include incorrect sizing of log files, archiving issues, excessive checkpoints, and sub-optimal parameter settings. Be sure to look for these first.
• Unexpected Performance Loss after Tuning
  This is a DBAs worse nightmare, but sometimes tuning SQL statement may result in decreased Oracle database performance. While the exact cause of such a regression isn't predictable, having it impact system performance can be avoided by using a test server to analyze SQL statement performance before launching to production environments.

Look for these and other common Oracle database performance issue when tuning your Oracle databases. Finding and repairing them will result increased database performance and decreased end user complaints.

Post by Josh Stein on behalf of Confio Software.

Top Tips for Breaking into the Competitive IT Industry

Due to the state of the economy, the IT industry is now more competitive than ever. People with careers in this field are constantly improving and gaining new skills and pushing their creativity and innovation to the limit in order to beat the competition. For someone who is new to the IT industry, breaking in can seem very difficult to impossible. Here are a few tips for breaking into the competitive industry that is IT.

Unlike a more static field like law, Information Technology is a field that is constantly changing and developing. New technology is always being developed and new skills are always popping up just waiting to be practiced and mastered. To successfully break into the IT industry, you're going to need to be informed of new developments when it comes to technology.

You need to stay current and be informed of all IT trends. Visit websites, such as Computer World and Tech Spot to ensure that you know all the necessary information to find and keep a job in the Information Technology industry.

Learning and development is important for all people in the IT industry. Since technology is always changing and new skills are constantly being developed, employees in the IT industry are going to have to constantly be learning mastering new skills to be employable. The IT industry is a fast-paced industry, and you won't survive if you aren't willing to change your ways and be very flexible.

In most professions, gaining new qualifications is greatly encouraged and recommended but not necessary. However, employers in the IT industry actually expect their employees to value and practice learning and development.

If you want to break into the competitive IT industry, you can get some certificates in Cisco, SQL, and UNIX. Although it is possible to get a job straight out of school, it's much better to get a few qualifications to give yourself an advantage over the tons of competition.

Fortunately, you don't need to spend a lot of money trying to get qualifications when you're in the IT industry. You just need to sacrifice some time and put in some effort. For most skills, you can learn them at home on the computer. In fact, there are many online courses that are actually for free. If you're looking for a career in the IT industry, you can practically get qualifications for free.

However, once you learn the skills, you're going to need to get certified, which almost always costs money. Google has a training center, and once you master the skills you were learning, you can take the corresponding certification exams. Each certification exam costs $50, but the qualifications look very good to employers on a resume.

Once you have the skills necessary and more, it wouldn't hurt to gain some experience. You can look around for internships or make your own samples of your work. If you get an internship, especially one that's paid, the company may decide to hire you at the end if you do your best.

As you can see, breaking into the IT industry isn't as hard as it seems, but you will need to exert some effort if you want to get a secure job in the IT industry that pays well.

Written by Lucy Hunt, a technology and business blogger with a keen interest in career development and the IT industry. Lucy currently writes on behalf of QA, leading providers of technical IT and learning development courses in the UK.

Compact Database Corruption in MS SQL Server

The concept of Database corruption still remains obscure in the minds of many database users and the very idea to deal with it would go in vain, if you do not plan out a perfect strategy at the right time. Most often, SQL database users come across compact database corruption and in majority of cases, the real culprit is not the database itself. 

The procedure described below shows how a page is read from the disk:

1. Initially, read the page from the disk. 

2. Now decrypt the page.

3. Calculate the checksum and verify with the expected value.

4. Determine whether it is the same page, which was expected as per the system pages. 

If steps ‘3’ and ‘4’ fail, you may receive the following errors on your screen: 

“Bad Checksum - idPage: %d, tyPage: %d, iPage: %d”

Or

“Page with valid ordinal not found - idPage: %d, iPage: %d”

 These errors indicate slight corruption in your database. Here are some possible reasons that could have triggered this corruption: 

·      
Improper shutting down of a device or you might have suspended a device and then resumed the operation. 

·      
If there are bugs in the underlying FAT/TFAT file system, you are very likely to face Compact file corruption. Even if you are using SD file for database storage, you may experience a similar thing. 

·       Moreover, SD cards might cause a number of problems during the Suspend/Resume cycles.  

However, it would be wrong to infer that Compact code bugs do not cause corruption. These bugs are more logical in nature. But, it would be right to say that they don't lead to physical corruptions, such as “checksum errors” or “page missing” errors. 

Indeed, compact implements a shadow paging mechanism to prevent corruption. When the Compact is performing a write operation to a file and you reboot the computer, it first writes the shadows of the original user data pages to the disk and then overwrites them with the shadows of the updated system pages. In this manner, the Compact performs a safe transaction write to the disk. Here, the changes are either completely reflected or not.    

About Author: Addision Philip is a technical writer and has written several articles on sql disaster recovery. You can see the articles from sql-server-recovery.blogspot.com.