The first column of data is the date and time stamp. The following output from typeperf is taken from a system that is swapping. typeperf -si 5 ”\Memory\Available Mbytes” ”\Memory\Pages/sec” The following is a typeperf command to report available memory and paging activity at 5 second intervals (the -si specifies the reporting interval).
It is easiest to illustrate a Windows system that is swapping using the output from the typeperf command. When the available memory, as reported by the \Memory\Available MBytes counter, is low and you observe paging activity, as reported by the \Memory\Pages / Second counter, the system is likely swapping. On Windows systems that include the Performance Monitor, monitoring memory pages per second (\Memory\Pages / second) and available memory bytes (\Memory\Available MBytes), can identify whether the system is swapping. To prove whether the lengthy garbage collection pauses are caused by swapping, you must monitor the system for swapping activity. If you observe lengthy garbage collections, it is a possibility that the system is swapping. If the garbage collection is a “stop the world” type of operation, one that stops all application threads from executing, a system that is swapping during a garbage collection is likely to experience lengthy JVM induced pause times. The time it takes to page in any portion of the Java heap into memory can dramatically increase the duration of a garbage collection.
If part of the Java heap has been swapped out it must be paged into memory so its contents can be scanned for live objects by the garbage collector. Swapping in from disk to memory can have a significant impact on an application’s responsiveness and throughput.Ī JVM’s garbage collector performs poorly on systems that are swapping because a large portion of memory is traversed by the garbage collector to reclaim space from objects that are unreachable. When a portion of an application is accessed that has been swapped out, that portion of the application must be paged in from the swap space on disk to memory. Usually the operating system swaps out a portion of an application that is executing the least frequently so as to not impact the applications or the portions of applications that are the busiest. When the amount of physical memory is exhausted by the applications running on the system, the operating system swaps out a portion of an application to swap space on disk. Swap space is typically allocated on a disk in a distinct disk partition. To deal with this potential situation, a system is usually configured with an area called swap space. Swapping occurs when there is more memory being consumed by applications running on the system than there is physical memory available. A Java application or JVM that is swapping or utilizing virtual memory experiences pronounced performance issues.