Question-: Which of the following are the causes for GC pauses in Cassandra database? A. lack of JVM space B. Mistuned JVM GC algorithm C. Slow disk D. High volume of data E. high number of nodes in Cassandra cluster
Answer: A,B,C Exp: GC pauses means when client submit the query it has to wait for longer period to get the response. GC pauses are not only because of the garbage collection, there are many other reasons which can cause the garbage collection issue but generally speaking. when you see the high number of pauses with fast safepoint indicates a lake of JVM heap. means not enough memory available for the JVM are you have not properly tuned this algorithm.
but when you see the high pauses with slow safepoints. which typically indicates that the JVM is having trouble entering a safe point. And that could be because of the slow disc drives. Cassandra database uses the memory mapped reads very heavily and JVM would not be aware about this disk latency comma so the JVM safepoint logic doesn't handle a blocking memory mapped read particularly well.
so suppose you see a very good average performance of the Cassandra database but you see a multi second JVM pauses. which code you mostly safepoint pauses could be caused by slow disk.
Admin Only
Question-: While analyzing the Cassandra cluster you found that one of the nodes in the ring is responding quite slow to query. Hence, you decided to debug the system and wanted to enable the log level to Debug only on that particular node. And once analysis is done, you wanted to reset the log level to INFO. Which of the following option you would use, so that you don’t have to restart the cluster? A. You would be changing the log level in logback.xml file. Which would be effective for next query B. You would be updating the log level by changing the JVM options. C. You will be using the nodetool setlogginglevel option. D. It is not possible, without node restart
Answer: C
Explanation: You can use the nodetool setlogginglevel which can directly talk to the processes. And does not require node to be restart. If you restart the node then this command would not be effective after restart. Below is the example through which you can enable the logging level to Debug, without the restarting of the node. nodetool setlogginglevels org,apache.cassandra.service.StorageProxy DEBUG
Similar to fetch the logging levels, you can use the following command option nodetool getlogginglevels Admin Only
Question-: You have setup Splunk process as well as Geneos alert system to analyze the logs. And they both can read the logs from a particular directory only. Now you need to make sure that the logs can be created in that directory only. How can you achieve this? A. You would be providing the log path at Cassandra.yaml file B. You will be providing the log path using the jvm.options C. You would be updating the log4j.properties file D. You would be updating the logback.xml file
Answer: B Exp: To change the logfile path, you have to use the jvm.options . You can use the logback.xml file for changing the log levels. Admin Only