Database Reference
In-Depth Information
cassandra> get Keyspace1.Standard2['mycol']['key888']
=> ( column=key888 , value=value888, timestamp=1277409950795000)
The server log records this query as follows:
DEBUG 13:06:03,291 get
DEBUG 13:06:03,292 weakreadlocal reading SliceByNamesReadCommand(
table='Keyspace1', key='mycol',
columnParent='QueryPath(columnFamilyName='Standard2',
superColumnName='null', columnName='null')',
columns=[key888,] )
This should give you enough information to follow along with what the server's doing as you
work.
Warning signs
There are a few things to look out for as you run Cassandra. For example, if you see something
like this in the logs with no further update, there's something wrong with the nodes in your ring:
DEBUG 12:39:56,312 attempting to connect to mywinbox/192.168.1.3
It's OK to attempt to connect, but then it should actually connect. It's possible for this to happen
when you mix Windows and Linux boxes in a Cassandra cluster, which is definitely not recom-
mended. If your Linux and Windows boxes can see each other, share resources such as printers,
read and write files between them, view web pages the other is serving, and so forth, this might
give you the impression that this should work. Don't be tempted to mix and match in a produc-
tion environment.
Overview of JMX and MBeans
In this section, we explore how Cassandra makes use of Java Management Extensions (JMX)
to enable remote management of your servers. JMX started as Java Specification Request (JSR)
160 and has been a core part of Java since version 5.0.
NOTE
You can read more about the JMX implementation in Java by examining the java.lang.management
package.
JMX is a Java API that provides management of applications in two key ways. First, JMX
allows you to understand your application's health and overall performance in terms of memory,
threads, and CPU usage—things that are generally applicable to any Java application. Second,
JMX allows you to work with specific aspects of your application that you have instrumented.
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