Home > Articles > Data

  • Print
  • + Share This
This chapter is from the book

JMX and MBeans

Built into Cassandra and the JVM is the capability to use the JMX, or Java Management Extensions. In other words, using JMX gives you the capability to manage your servers remotely or check into settings programmatically, including the memory, CPU, threads, Gossip, or any other part of the system that has been instrumented in JMX. Instrumentation is what enables the application to provide application-specific information to be collected by external tools. JMX also gives you the ability to control certain aspects of this information.


MBeans, or Managed Beans, are a special type of JavaBean that makes a resource inside the application or the JVM available externally. The standard tool that ships with Java for managing the MBeans is JConsole.

The most common use case for accessing a Cassandra server is that the server will be remote and you probably won’t have console access to it. It is also highly recommended that you run JConsole remotely as it is a heavy user of resources on a machine and can steal those resources away from the Cassandra node. If this is the case, you can use SSH tunneling to bring up JConsole. When you SSH, be sure to use the –X switch to ensure that X11 forwarding is on. This is what enables you to use JConsole over the network. After SSHing into the machine running Cassandra and finding the JConsole binary, just execute it as you would any normal binary. Assuming everything is configured correctly, you will get a JConsole login window as shown in Figure 8.1.

Figure 8.1

Figure 8.1 JConsole login window when logging in via localhost

Click on the radio button labeled Remote Process and type localhost:7199. If you have Cassandra set up with authentication, you will need to put in the username and password as well. Port 7199 is the default JMX port for Cassandra. The first thing you will notice once a connection has been established is that there are multiple tabs that contain information for you to look through. These tabs are Overview, Memory, Threads, Classes, VM Summary, and MBeans.

The Overview, Memory, and Threads tabs are sets of graphs that provide insight into the current state of the system. The Classes graph is simply a graph of how many classes are loaded into the JVM at the current time (or a different time range that you choose). The VM Summary is an overview of what the current view of the Java Virtual Machine is.


The Memory tab consists of graphs about the current state of the memory (see Figure 8.2). One of the most important memory stats that you want to be aware of is your current heap usage. It is also the default graph that comes up on the Memory tab. As with everything else in your system, it is helpful to know what a good baseline is for heap usage during normal system operations. If you have a 10GB heap set and you find during most of your operations that you are using only 3GB, you can likely reduce your JVM maximum heap size. This will enable you to reduce your memory footprint on the system and possibly even speed up your GCs.

Figure 8.2

Figure 8.2 JConsole Memory tab displaying heap usage graphs

Cassandra also does a lot of work off-heap. Things like bloom filters in version 1.2 and forward are off-heap now. Keeping tabs on what the off-heap memory usage looks like is also very important.

Garbage collection is also one of the metrics that can be viewed from the Memory tab. If needed (though typically not recommended unless you know what you are doing), you can even force a GC from the Memory tab in JConsole. In Cassandra 1.1 and later, there are even helpful bars that display the total memory used versus memory available both on-heap and off-heap.


The Threads tab in JConsole is dedicated to showing the current and peak usage patterns of various thread stages in Cassandra (see Figure 8.3). These include everything that you would normally see in the logs from things like the CommitLog handler and compaction scheduler all the way to garbage collection, Gossip, and streaming. It is also helpful here to see how many threads your system uses normally as well as under load.

Figure 8.3

Figure 8.3 JConsole Threads tab displaying the number of threads Cassandra is currently using and general information on the main Cassandra thread


The final tab in JConsole is the tab for MBeans (see Figure 8.4). There are a lot of MBeans that are useful for assessing the state of your Cassandra node and your Cassandra cluster. You will notice that there are a few groupings here that can be expanded. Other than the standard Java MBeans that are available to every agent, there are several groupings specific to Cassandra. All of their class paths start with org.apache.cassandra.

Figure 8.4

Figure 8.4 JConsole MBeans tab view with the Cassandra DB and Internal trees opened

There are a lot of MBeans provided by an application as complex as Cassandra. There is no need to cover all of them as you can easily explore them on your own using the JConsole interface.

As a high-level overview, they are broken down into the following categories:

  • DB. The MBeans stored in the DB section cover everything about the actual data storage part of Cassandra. You can view information about the cache and CommitLogs, or even information about the individual ColumnFamilys that you have created in each of the keyspaces. HintedHandoffManager, EndPointSnitchInfo, and CompactionManager information can also be found here.
  • Internal. In the Internal section, there are MBeans that cover the state and statistics around the staged architecture. More specifically, you can find information about the state of Gossip and HintedHandoff as opposed to just finding information about the managers as in the DB section.
  • Metrics. The metrics available in this section are ClientRequestMetrics. These are things like read and write timeouts and Unavailable errors.
  • Net. The network section houses information about internode communication. This includes information about the FailureDetector, Gossiper, MessagingService, and StreamingService.
  • Request. The MBeans in the Request section are about tasks related to read, write, and replication.

When you select any MBean in the tree, its MBeanInfo and MBean descriptor are displayed on the right-hand side of the window. If any additional attributes, operations, or notifications are available, they will appear in the tree as well, below the selected MBean.

Each one of these sections of MBeans provides access to a large amount of information, giving you insight into both the system as a whole and the individual nodes. Familiarizing yourself with what is available to you as an admin will help you when it comes time to instrument JMX-level checks from within your monitoring system.

  • + 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