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Lesson 5Disk I/O and Oracle
ObjectiveExplain the importance of disk I/O to Oracle database performance.

Disk I/O | Database Performance

One of the critical issues with Oracle database tuning is the time required to perform an I/O operation on disk. When Oracle requests a data block, this request translates into an OS request for the operating system to fetch a data block from a disk device.
The Slide Show below illustrates this.

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The most time consuming of these processes is reading the data block from disk.
Reading the data block from disk
Reading the data block from disk

I/O Performance Factors

To review, a disk I/O can take several milliseconds, which does not sound like much time, but databases that perform hundreds of I/O per second will suffer a degradation in response time.
The time required to service an I/O (called latency) is the sum of the rotational delay on the disk, the seek delay as the read/write heads position themselves under the proper cylinder, and the data transmission time to the database server.

latency equation
latency equation

We will devote an entire module to disk I/O, which is the single largest component of OS response time.
The next lesson looks at memory usage in the OS environment.