Using the Garbage Collections Page

The Garbage Collections page contains information related to GC activity.

This page displays information about garbage collection and memory allocation in tables and graphs.

Using the Garbage Collections Page: Selections and Aspects

Use the drop-down menus at the top of the page to choose a selection and aspect if desired. Data from other pages can be saved to the selection drop-down menu by dragging an area of a chart (or selecting data from a table) and choosing Store Selection or Store Selection and Set As Focused Selection from the context menu.

The following controls provide additional behavior:

Show concurrent: Show all events concurrent to the selected aspect.
Contained: Only show events that are fully contained in the time range from the active selection aspect
Same threads: Only show events in threads related to the active selection aspect.
Time Range: Zoom to time range on relevant places on the page, or clear the time range zoom.

Using the Garbage Collections Page: Tables and Graphs

Table columns are labeled as follows:

GC ID: The garbage collection ID.
Cause: The reason for triggering this garbage collection.
Collector Name: The name of the garbage collector.
Longest Pause: The longest individual pause during the garbage collection.
Sum of Pauses: The total duration that Java execution was paused during the garbage collection.
Final References: The number of final references.
Weak References: The number of weak references.
Soft References: The number of soft references.
Phantom References: The number of phantom references.

Additional information is available in the following subtabs, which can be filtered for a specific Garbage Collection by selecting a GC from the adjacent table:

Pause Phases: Displays the pause events that occurred during the selected garbage collection as well as each event's duration, start time, and the thread it occurred in.
Metaspace: Shows various metaspace statistics before and after the selected Garbage Collection

You can select any of the following to be displayed on the graph:

Used Heap: Memory allocated by objects on the heap.
Heap Space: Committed Size: Size of the committed memory for the virtual space.
Heap Space: Reserved Size: Size of the reserved memory for the virtual space.
Metaspace: Used: Memory allocated by objects in the metaspace.
Metaspace: Committed: Memory committed for the metaspace.
Metaspace: Reserved: Memory reserved for the metaspace.
Longest Pause: The duration of the longest GC pause.
Sum of Pauses: The total duration of all GC pauses.
Pause Phases: Phases of the garbage collection pauses.
Thread Activity: Allows you to view the thread activity of a selected thread from the Pause Phases tab.

Using the Garbage Collections Page: Configuring Rules

You can set configuration attributes for the rules associated with this page by clicking the Edit Configuration icon.

The following options are available:

GC Pause Peak Duration

GC pause warning limit: The GC pause time needed to trigger a warning.

GC Pauses

GC pause ratio info limit: Ratio between GC pauses and execution time over the set time window needed to trigger an info notice.
GC pause ratio warning limit: Ratio between GC pauses and execution time over the set time window needed to trigger a warning.
GC pause time window size: The time window size used when evaluating the rule.

GCs Caused by GC Locker

GC locker ratio limit: Warning limit ratio between number of garbage collections caused by GC locker and total garbage collections.

GCs Caused by Heap Inspection

Heap inspection GC limit: Warning limit ratio between number of heap inspection garbage collections and total garbage collections.

GCs Caused by System.gc()

System.gc() ratio limit: Warning limit for ratio between System.gc() and total garbage collections.