{"id":20306,"date":"2013-05-10T12:49:34","date_gmt":"2013-05-10T07:19:34","guid":{"rendered":"http:\/\/vskills.in\/certification\/tutorial\/?p=20306"},"modified":"2024-04-12T14:16:40","modified_gmt":"2024-04-12T08:46:40","slug":"heap-and-thread-monitoring","status":"publish","type":"page","link":"https:\/\/www.vskills.in\/certification\/tutorial\/heap-and-thread-monitoring\/","title":{"rendered":"Heap and thread monitoring"},"content":{"rendered":"

Certify and Increase Opportunity.<\/span>
\nBe <\/span>
\nGovt. Certified Apache Cassandra Professional
\n<\/span><\/a><\/p>\n

Heap and thread monitoring<\/strong><\/p>\n

\"binary<\/a><\/p>\n

While Java takes care most of the details of memory and heap management, situations can occur where memory is never reclaimed. This recipe uses two java tools jmap and jhat, to capture a heap dump and examine it.<\/p>\n

Steps to complete it
\nDetermine the pid of a running java process
\n$ ps -ef | grep java
\nedward    3736     1  1 01:46 pts\/0    00:00:06<\/p>\n

Use the jmap tool to dump the heap to a file.
\n$ jmap  -dump:file=b  3736
\nDumping heap to \/home\/edward\/hpcas\/b \u2026
\nHeap dump file created<\/p>\n

Start a jhat web server on 7001 (this defaults to 7000 the cassandra storage port.
\n$jhat -port 7001 \/home\/edward\/hpcas\/b
\nChasing references, expect 15 dots\u2026\u2026\u2026\u2026\u2026
\nEliminating duplicate references\u2026\u2026\u2026\u2026\u2026
\nSnapshot resolved.
\nStarted HTTP server on port 7001
\nServer is ready.<\/p>\n

Jhat and jmap allow you to capture and review heap dumps. This is a valuable tool when chasing down memory leaks or un-explained memory usage.<\/p>\n

Tuning Java Heap<\/span><\/p>\n

Because Cassandra is a database, it spends significant time interacting with the operating system’s I\/O infrastructure through the JVM, so a well-tuned Java heap size is important. Cassandra’s default configuration opens the JVM with a heap size that is based on the total amount of system memory:<\/p>\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n
System Memory<\/th>\nHeap Size<\/th>\n<\/tr>\n<\/thead>\n
Less than 2GB<\/td>\n1\/2 of system memory<\/td>\n<\/tr>\n
2GB to 4GB<\/td>\n1GB<\/td>\n<\/tr>\n
Greater than 4GB<\/td>\n1\/4 system memory, but not more than 8GB<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

General Guidelines<\/strong><\/p>\n

Many users new to Cassandra are tempted to turn up Java heap size too high, which consumes the majority of the underlying system’s RAM. In most cases, increasing the Java heap size is actually detrimental for these reasons:<\/p>\n