There are two forms of garbage collection, lazy and aggressive. These terms describe two distinct tests for finding empty pages.
Lazy garbage collection refers to an inexpensive test to find empty pages. This test may not be effective during long-running transactions, and empty pages may accumulate. Lazy garbage collection is inexpensive to use, but can lower performance. Performance is affected by the fragmentation of space allocated to a table, and by the accumulation of empty pages that must be evaluated during queries.
Aggressive garbage collection refers to a sophisticated test for empty pages. This test is more expensive than the lazy garbage collection test, because it checks each deleted row in a page to determine whether that deleting transactions are committed.
Both the delete command and the housekeeper garbage collection task can be configured for aggressive or lazy garbage collection, through the configuration parameter enable housekeeper GC.
The aggressive housekeeper garbage collection self-tunes the frequency with which the housekeeper garbage collection task examines the housekeeper list, so that the frequency of examination matches the rate at which the application generates empty pages.
