Page 6 of the the document Memory Management in the Java HotSpot™ Virtual Machine contains the following paragraphs:
Young generation collections occur relatively frequently and are efficient and fast because the young generation space is usually small and likely to contain a lot of objects that are no longer referenced.
Objects that survive some number of young generation collections are eventually promoted, or tenured, to the old generation. See Figure 1. This generation is typically larger than the young generation and its occupancy grows more slowly. As a result, old generation collections are infrequent, but take significantly longer to complete
Could someone please define what "frequent" and "infrequent" mean in the statements above? Are we talking microseconds, milliseconds, minutes, days?