Home > Articles > Operating Systems, Server > Solaris

  • Print
  • + Share This
Like this article? We recommend

STEP 5. Monitoring and Tuning a Database

A well-tuned database system has the following characteristics:

  • The system is mostly CPU-bound.

  • Disk I/O is well-balanced.

  • The buffer cache is working effectively.

  • The database is configured to run efficiently.

As we have already noted, the applications must also be coded efficiently if the database system is to run efficiently.

Having investigated memory, disks, networks and CPUs, you need to undertake the final step: monitor and tune the database, a process explored in detail in the following chapters of Configuring and Tuning Databases on the Solaris Platform for Oracle, Sybase, Informix, and DB2. Monitoring and tuning the buffer cache is a vital element of database tuning. A brief review of the main issues is presented in the next section, but before proceeding to the database tuning chapters, you would do well to review Chapter 7, which is dedicated to the buffer cache. Finally, although application efficiency is a crucial component in any well-tuned system, we will not be considering it since it is beyond the scope of this document. Refer to Techniques for Optimizing Applications: High Performance Computing, by Rajat Garg and Ilya Sharapov, Sun Microsystems Press, 2001 for a discussion on application optimization.

The Buffer Cache

One of the main metrics in monitoring database performance for OLTP workloads is the buffer cache hit rate. The buffer cache stores in memory as many database blocks read from disk as possible. The expectation is that the same database blocks will often be used by different transactions; the buffer cache hit rate shows how often a requested block was retrieved from the cache rather than from the disk. Since memory access is so much faster than disk access, a high cache hit rate is important for good performance with OLTP workloads.

For DSS workloads the buffer cache is less important. Some databases (for example, Oracle and Informix) avoid the buffer cache entirely when carrying out table or index scans. DB2 for Solaris does use the buffer cache, but there may be little opportunity for reuse of buffers since the volume of data brought into the cache is typically much greater than the cache size. So, cache buffers tend not to stay in the buffer for long. Similar behavior applies to batch jobs processing large volumes of data.

A Closer Look at the Cache Hit Rate

The cache hit rate can be misleading. For example, how much better is a 95% cache hit rate than a 90% cache hit rate? Does it represent a 5% improvement?

The answer is no! A 90% cache hit rate means 90% of all read I/Os are satisfied from the cache—only 10% of the reads result in a physical disk access. A 95% cache hit rate means only 5% of reads go to disk. So, improving the cache hit rate from 90% to 95% means physical disk reads are halved, not improved by only 5%! Depending on the number of physical reads, halving them may make a significant difference to the load on the disks.

Given this potential confusion, it is often more useful to think in terms of the miss rate (100 minus cache hit rate).

You can usually improve the cache hit rate by increasing the size of the database buffer cache, although a point is eventually reached when any improvement is not worth the extra memory. Cache sizing and effectiveness are discussed in more detail in Chapter 7 of Configuring and Tuning Databases on the Solaris Platform.

An Appropriate Cache Hit Rate

A cache hit rate of 80% might be quite suitable in one situation while a much higher hit rate of 95% might be inadequate in another. How can you tell when you need to increase the size of the buffer cache to try to improve the cache hit rate?

You should consider three factors when determining an appropriate cache hit rate:

  • The amount of memory available. Avoid paging at all costs. If increasing the size of the buffer cache causes application paging, then it is better to leave the cache as it is. If free memory is available, then increasing the cache is an option.

  • The load on the database disks. Determine the disk utilization of the database disks by looking at either iostat, sar, or statit statistics for the relevant disks. Check, too, how many of the I/Os are due to reads. If the database disks are showing high utilization or high service times (as defined in "STEP 2. Monitoring Disks" on page 9) and a significant number of the I/Os are reads, then increasing the cache hit rate could take the pressure off the disks.

  • Application response times. Retrieving disk blocks from the cache is faster than retrieving them from disk and also consumes less CPU. So improving cache hit rate might also reduce response times. Many factors contribute to response times, though, so any improvement may be less than you were hoping for.

Aftereffects of Database Monitoring and Tuning

Given that the database may be the major application on the system, investigating the behavior of the database should shed further light on the data already collected. Monitoring and tuning the database is an iterative process. Tuning the database may change the behavior of the system, in which case it will be important to briefly revisit the previous steps covered in the chapter.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020