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Lesson 8

Disk IO Tuning Conclusion

In this module, we covered the main points of one of the most important aspects of Oracle tuning.

Main points discussed in the Disk I/O Tuning Module

Here are the main points from this module.
  1. Disk I/O is the largest component of response time for any Oracle database.
  2. The iostat utility can be used to measure I/O against physical disks.
  3. Iostat information can be stored in Oracle tables for analysis.
  4. Disks that have a disproportional amount of I/O become hot.
  5. The iostat utility can be used to identify hot disks.
  6. In some cases hot disks can lead to I/O bottlenecks.
  7. Once a hot disk is identified, the DBA must learn which Oracle data files reside on that disk.
  8. A physical disk is mapped onto UNIX filesystems or mount points.
  9. The bstat-estat utility can be run to see that data files are active during a specific period.
  10. Hot files should be moved onto less active data disks.
  11. Striping can be used to move a single hot data file into multiple data files.
  12. OS striping can be used to evenly spread data files across disks.
  13. Small, highly active tables can be spread across data blocks by making PCTFREE small

Module review

You should be familiar with the following concepts in order to tune the memory of your OS:
  1. The OS will freely allocate memory to all tasks on the database server.
  2. When the Oracle database starts, RAM memory is allocated for the SGA.
  3. Dedicated listener processes will also consume memory according to the sort_area_size init.ora parameter.
  4. vmstat utility is a great way to monitor memory swapping.
  5. The pi column in vmstat shows memory swapping.
  6. Savvy DBAs often store vmstat data inside Oracle tables for later analysis.
  7. If you experience memory swapping you can reduce the SGA size, reduce sort_area_size, or implement the multi-threaded server.

Now you should be able to:
  1. Execute and interpret iostat
  2. Define a hot disk
  3. Identify files that are causing high I/O
  4. Stripe a data file
  5. Explain OS file striping techniques
  6. Stripe a table with PCTFREE

Glossary Terms

Here are some terms from this module that may be new to you.
  1. bottleneck: Any impediment or obstacle that causes a performance slow down on a computer or network.
  2. data striping: Distribute a hot data file across numerous physical disks.
  3. hot disk: A disk that is having a disproportional amount of I/O compared to the other disks.
  4. iostat: A utility that provides a time measure of the amount of physical I/O that has been addressed to the disk devices.
  5. load balancing: The distribution of connections among Oracle listeners to ensure that incoming requests do not have to wait for a listener connection.
  6. logical volume striping: Striping a data file across numerous UNIX logical disk pieces.
  7. PCTFREE parameter: The Oracle table parameter that causes a data block to be un-linked from the freelist.
  8. RAID0+1: Also called RAID 10, it is a combination of mirroring and striping.
The next module explores tuning for OS memory usage.

Oracle hot Disks - Quiz

To complete this module, click the Quiz link below to test your knowledge of tuning for disk I/O.
Oracle hot Disks - Quiz