100% full Eden space, 0% used Survivor space - Garbage collection not done

Question

I have encountered a rather confusing GC case: While the Eden space is 100% full, 0% survivor space is used. When the Eden is full, garbage collection should be triggered, right? Can there be a case in which the GC daemon is prevented from running? Like a 100% CPU? We are using `jdk-1.7`. What can be the cause? Below is the jmap output. We also tried to capture a more detailed memory usage using `jmap -histo -F`, but then the CPU usage dropped to 0% and the java process became unreachable. ``` using thread-local object allocation. Parallel GC with 18 thread(s) Heap Configuration: MinHeapFreeRatio = 40 MaxHeapFreeRatio = 70 MaxHeapSize = 12884901888 (12288.0MB) NewSize = 1310720 (1.25MB) MaxNewSize = 17592186044415 MB OldSize = 5439488 (5.1875MB) NewRatio = 2 SurvivorRatio = 8 PermSize = 21757952 (20.75MB) MaxPermSize = 85983232 (82.0MB) G1HeapRegionSize = 0 (0.0MB) Heap Usage: PS Young Generation Eden Space: capacity = 4265738240 (4068.125MB) used = 4265738240 (4068.125MB) free = 0 (0…

Accepted Answer

When i see at your Heap Configuration i found that

`MaxNewSize = 17592186044415 MB` is incorrect however it must be in bytes.

What i see that almost all generations are full and same time and `Collector` is trying to collect both the generations so they are blocking each other.

I suggest to please tune the memory with below parameters .

```
-XX:NewRatio=3 - the young generation will occupy 1/4 the overall heap
-XX:NewSize - Calculated automatically if you specify -XX:NewRatio
-XX:MaxNewSize - The largest size the young generation can grow to (unlimited if this value is not specified at command line)
```

I also suggest to use some survivor space it will give time collector when objects being copied from `eden` to 'tenured' generation.

```
-XX:SurvivorRatio=6 - each survivor space will be 1/8 the young generation
```

If survivor spaces are too small copying collection overflows directly into the tenured generation.

For any clarification refer this link.

Edit:

`-XX:NewRatio=3` - the young generation will occupy 1/4 the overall heap

Calculation:

```
    y/t=1/3

y+t=h
    y+3y=h
    y=h/4

t=tenured
 y=young
 h=heap
```

100% full Eden space, 0% used Survivor space - Garbage collection not done

Solution

Problem