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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 Update 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, PS MarkSweep and PS Scavenge). Each tab contains a table with the following default attributes:
Total Collection Time
Collection Count
GC Start Time
GC End Time
GC Duration
GC ID
GC Thread Count
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.
To configure the appearance of the table, click the Table Settings button in the top right corner of the Active Memory Pools panel and select the columns that you want to show or hide. For each column, you can set the minimum width, weight and initial sort order.