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backup disk using all of the remaining disks and parity information. Depending on the RAID level used, this system will continue to work with one disk failure (RAID-5) or with two disk failures (RAID-6). The greatest problem exists in terms of performance because of the increased read/ writes required to maintain parity in the array. The need to maintain parity can become a bottleneck.
A brief description of common RAID levels follows :
RAID uses arrays of inexpensive disks to maximize disk performance and data availability. Although the usage of disk mirroring, striping, and parity are not new, RAID combines these elements to provide improved data storage. Across the various official and vendor_defined RAID levels, these three elements are mixed in an attempt to balance data redundancy versus disk performance. Considering the current disk storage trends, this balancing act seems likely to continue. The DBA should keep in mind that the use of RAID is usually determined by systems personnel and that he or she might be required to operate under a RAID level not optimal for his or her database.
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view the current configuration of these interprocess communications (IPC) settings by issuing the UNIX ipcs(1) command.
The DBA should always consider network performance when evaluating his or her application environment. There are specific tunable parameters that, if set incorrectly, can cause serious performance problems for the application. Reliable performance statistics should be gathered and maintained so that proper workload determinations can be made. Please keep in mind that if the network environment cannot sufficiently support your user community, no amount of operating system tuning will resolve your performance problems. Also keep in mind that an application will more than likely perform differently when operating in a wide area network (WAN) than in a local area network (LAN). This is because your applications data is traveling greater distances (often called hops)through special equipment (routers) designed to manage the WAN. There is additional network overhead in this environment, so expect to see different performance issues when you compare your WAN and LAN statistics. If you begin to experience poor performance with your applications, consider including your network administrator in your efforts to resolve the performance problems.
CAUTION |
It is not advisable to change the operating system priority of the Oracle background processes. If these values are altered , the database might process information less efficiently . If you must modify them, set all the database processes to the same value. |
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There are two options available with Oracle that immensely enhance overall database application performance. The two options discussed in this section are the parallel server option and the parallel query option. Both of these options ”although each serves its own purpose ”maximize use of system resources to achieve very much improved database performance, especially on very large queries.
You can use the parallel server option (which can be purchased separately from the Oracle server software) to access common data files on a server from databases on two or more servers. Each server has its own CPU and memory, but share the same disk drives . In turn , databases on these servers share the same set of database files. As a result, many benefits are experienced , ranging from high database availability to increased performance.
Suppose that you had a cluster of two servers, each server housing a database and each database sharing common data files. If database 1 fails for some reason (for example, hardware failure), the users of database 1 can be redirected to database 2. Database 2 may be used as a backup to database 1, and vice versa.
Gains in performance will also be experienced because the processing for each database occurs on each individual server. The two similar databases live on a server with their own memory and CPU; thus, they utilize their own resources. Memory contention and CPU usage are drastically decreased and may be decreased further in the future by adding another server to the cluster. The only things shared are the data files.
The parallel query option is the option of taking advantage of the availability of more than one CPU on a server. By using this option with multiple CPUs, database queries can be divided by Oracle into several smaller queries and assigned to multiple processes. Each process resolves its query and then merges the results into a single result set. This process is know as parallelization , or parallelism. The parallel query option is particularly useful in a data warehousing or decision-support environment, where complicated and summarized queries are run and batch transactions are involved in populating the database.
NOTE |
Oracle8 supports the capability of performing INSERT, UPDATE, and DELETE transactions in parallel in addition to the SELECT statement in previous releases. Performing data manipulation in parallel provides the potential for data to be populated in batch, in a fraction of the time compared to that of not using the parallel option. |