DA0005: Frequent GC2 collections

Cause

A high number of .NET memory objects are being reclaimed in generation 2 garbage collection.

Rule Description

The Microsoft .NET common language runtime (CLR) provides an automatic memory management mechanism that uses a garbage collector to reclaim memory from objects that the application no longer uses. The garbage collector is generation-oriented, based on the assumption that many allocations are short-lived. Local variables, for example, should be short-lived. Newly created objects start in generation 0 (gen 0), and then they progress to generation 1 when they survive a garbage collection run, and finally transition to generation 2 if the application still uses them.

Objects in generation 0 are collected frequently and usually very efficiently. Objects in generation 1 are collected less frequently and less efficiently. Finally, long-lived objects in generation 2 should be collected even less frequently. Generation 2 collection, which is a full garbage collection run, is also the most expensive operation.

This rule fires when proportionally too many generation 2 garbage collections have occurred. If too many relatively short-lived objects survive generation 1 collection but are then able to be collected in a generation 2 full collection, the cost of memory management can easily become excessive. For more information, see the Mid-life crisis post on the Rico Mariani's Performance Tidbits on the MSDN Web site.

How to Investigate a Warning

Review the Profiling Tools .NET Memory Data Views reports to understand the application’s pattern of memory allocation. Use the Object Lifetime View to determine which of the program’s data objects are surviving into generation 2 and then being reclaimed from there. Use the .NET Memory Allocations View to determine the execution path that resulted in these allocations.

For information about how to improve garbage collection performance, see Garbage Collector Basics and Performance Hints on the Microsoft Web site. For information about the overhead of automatic garbage collection, see Large Object Heap Uncovered.