Using the Memory Tab

The Memory tab allows you to monitor how efficiently your application is using memory resources. This tab focuses on heap usage, garbage collection, and active memory pools. The information provided on this tab helps you determine whether you have configured the JVM to provide optimal application performance.

From the Memory tab, you can manually initiate a full garbage collection using the Run a full garbage collection button in the top right corner of the tab.

Heap Histogram

The top panel of the Memory tab contains the Heap Histogram. The Heap Histogram feature can be used to look at the distribution of the memory on the heap per class. Since it can incur some latency and overhead, it is captured on demand only. To capture a snapshot, click the Refresh Heap Histogram button. You will be presented with a warning letting you know that this can cause some overhead. When the first heap histogram is captured, that will be the baseline, and the delta will be set to zero. Every subsequent histogram captured will show the delta to the second last. If the Reset delta calculation is pressed, the currently captured snapshot will be used as baseline.

GC Tables

The GC Tables panel contains the current values for key performance attributes of available garbage collectors. The panel is divided into tabs with the names of the active garbage collectors (for example, G1 Young Generation and G1 Old Generation). Each tab contains a table with the following default attributes:

• Total Collection Time: The accumulated collection time.

• Collection Count: The total number of collections that have occurred.

• GC Start Time: The start time of this GC since the JVM was started.

• GC End Time: The end time of this GC since the JVM was started.

• GC Duration: The elapsed time of this GC.

• GC ID: The identifier of this GC, which is the number of collections that this collector has done.

• GC Thread Count: The number of GC threads.

By right-clicking an attribute, you can change its update interval, units, and for some attributes it is possible to set the value.

Active Memory Pools

The Active Memory Pools panel contains a table with information about memory pools available to the JVM. By default, the table contains the following columns:

• Pool Name: The name of the memory pool.

• Type: The type of the memory pool. If the memory pool belong to the Java heap, then the type is HEAP, otherwise, it is NON_HEAP.

• Used: Currently used size of the memory pool.

• Max: Maximum size of the memory pool.

• Usage: Percent of the maximum memory pool size that is currently used.

• Peak Used: The peak value for the used size of the memory pool during the lifetime of the monitored JVM.

• Peak Max: The peak value for the maximum size of the memory pool during the lifetime of the monitored JVM.

To filter the memory pools, select the filter column (usually, the pool name) and specify the filter string in the text field above the table.