Eden is the young-generation heap region where newly allocated Java objects initially reside. It is cleaned frequently because many new objects are created and discarded there. section 11.1
Objects that remain useful after garbage-collection cycles can move from Eden to Survivor regions and eventually to the Old Generation. Reading these transitions helps connect allocation behavior with GC activity. section 11.1 section 11.5
Reading Eden changes in a GC log
A log entry such as “Eden regions: 4->0(5)” shows that a collection emptied four occupied Eden regions, leaving zero afterward, with a capacity of five regions. If Survivor regions rise from 0 to 1 while Old regions remain at 0, some objects survived the collection without yet reaching the old generation. section 11.1
Listing 11.3 Logs that show the changes after a collection
[1.342s][info][gc,heap] GC(0) Eden regions: 4->0(5) #1 [1.342s][info][gc,heap] GC(0) Survivor regions: 0->1(1) #2 [1.342s][info][gc,heap] GC(0) Old regions: 0->0 #3 [1.342s][info][gc,heap] GC(0) Humongous regions: 0->0 #4
Inspect the Eden, Survivor, Old, and Humongous region counts reported before and after a collection. section 11.1
