Memory usage and Oracle Database Performance

Memory within an OS environment consists of Random Access Memory (RAM) chips. Like the SIMS chip on your PC provides you with 64 megabytes of RAM, your database server also contains a memory region.
As we all know, RAM memory is 10,000 times faster than disk, and most RAM chips can read information in nanoseconds (billionths of a second).

The operating system manages the shared memory resource. Whenever the demands for RAM memory exceed the physical memory capacity, the OS swaps some of the memory contents onto disk and frees memory for other tasks.
The OS allocates memory as requested, adding new memory segments from low memory to high memory. Here is how it works:

Paging, also known as virtual memory paging, is a process by which the operating system moves data from the computer's RAM (Random Access Memory) to the hard disk to free up memory for other processes. When an Oracle database is paged out, its performance can be impacted in several ways. Here are some ways that paging can affect the performance of an Oracle Database:

1. Slower response time: Paging causes slower response times for Oracle database operations because data must be retrieved from the disk instead of from the RAM. This can result in longer query times and slower transaction processing.
2. Increased I/O: Paging increases the amount of I/O (input/output) activity on the system because data must be read from or written to the hard disk. This can result in higher disk usage and slower performance.
3. Resource contention: Paging can cause resource contention on the system because multiple processes are competing for the same disk and memory resources. This can lead to increased wait times and slower performance.
4. Poor cache hit ratio: Paging can result in a lower cache hit ratio, which is the percentage of data that is retrieved from cache instead of from the disk. A low cache hit ratio means that more data must be retrieved from the disk, which slows down performance.
5. Increased CPU usage: Paging can increase CPU usage because the operating system must manage the process of moving data between the RAM and the hard disk. This can result in slower performance and reduced capacity for other tasks.

To mitigate the performance impact of paging on an Oracle database, it is recommended to:

1. Allocate sufficient RAM to the database server to minimize the need for paging.
2. Monitor the paging activity of the database server to detect any issues.
3. Tune the Oracle database parameters to optimize performance, such as the buffer cache size and the sort area size.
4. Monitor and optimize the I/O subsystem to reduce disk I/O and improve performance.
5. Regularly analyze and tune the SQL queries to reduce their impact on system resources

In summary, paging can have a significant impact on the performance of an Oracle database, resulting in slower response times, increased I/O, resource contention, poor cache hit ratio, and increased CPU usage. By allocating sufficient memory, monitoring paging activity, tuning database parameters, optimizing the I/O subsystem, and analyzing SQL queries, the performance impact of paging can be minimized, and the database can perform optimally.

The process of paging can greatly slow down the performance of an Oracle database, since paged-out memory segments are unavailable to the database. We will cover the monitoring of memory in a later module.
The next lesson looks at CPU usage within Oracle.