Caused by: java.lang.OutOfMemoryError: GC overhead limit exceeded

Caused by: java.lang.OutOfMemoryError: GC overhead limit exceeded

问题描述:

本地爬虫服务抛出异常java.lang.OutOfMemoryError：GC overhead limit exceeded
导致服务起不来，查看日志发现加载了太多资源到内存，本地的性能也不好，gc时间消耗的较多。

解决方案:

增加参数，-XX:-UseGCOverheadLimit，关闭这个特性;
同时增加heap大小，-Xmx1024m。

Y分析:

OOM大家都知道，就是JVM内存溢出了，那GC overhead limit exceed呢？

GC overhead limt exceed检查是Hotspot VM 1.6定义的一个策略，通过统计GC时间来预测是否要OOM了，提前抛出异常，防止OOM发生。Sun 官方对此的定义是：“并行/并发回收器在GC回收时间过长时会抛出OutOfMemroyError。过长的定义是，超过98%的时间用来做GC并且回收了不到2%的堆内存。用来避免内存过小造成应用不能正常工作。“

GC overhead limit exceed HotSpot的实现：

bool  print_gc_overhead_limit_would_be_exceeded = false;

if  (is_full_gc) {

if (gc_cost() > gc_cost_limit &&

free_in_old_gen < (size_t) mem_free_old_limit &&

free_in_eden < (size_t) mem_free_eden_limit) {

// Collections, on average, are taking too much time, and

//      gc_cost() > gc_cost_limit

// we have too little space available after a full gc.

//      total_free_limit < mem_free_limit

// where

//   total_free_limit is the free space available in

//     both generations

//   total_mem is the total space available for allocation

//     in both generations (survivor spaces are not included

//     just as they are not included in eden_limit).

//   mem_free_limit is a fraction of total_mem judged to be an

//     acceptable amount that is still unused.

// The heap can ask for the value of this variable when deciding

// whether to thrown an OutOfMemory error.

// Note that the gc time limit test only works for the collections

// of the young gen + tenured gen and not for collections of the

// permanent gen.  That is because the calculation of the space

// freed by the collection is the free space in the young gen +

// tenured gen.

// At this point the GC overhead limit is being exceeded.

inc_gc_overhead_limit_count();

if (UseGCOverheadLimit) {

if (gc_overhead_limit_count() >=

AdaptiveSizePolicyGCTimeLimitThreshold){

// All conditions have been met for throwing an out-of-memory

set_gc_overhead_limit_exceeded(true);

// Avoid consecutive OOM due to the gc time limit by resetting

// the counter.

reset_gc_overhead_limit_count();

} else {

// The required consecutive collections which exceed the

// GC time limit may or may not have been reached. We

// are approaching that condition and so as not to

// throw an out-of-memory before all SoftRef's have been

// cleared, set _should_clear_all_soft_refs in CollectorPolicy.

// The clearing will be done on the next GC.

bool near_limit = gc_overhead_limit_near();

if (near_limit) {

collector_policy->set_should_clear_all_soft_refs(true);

if (PrintGCDetails && Verbose) {

gclog_or_tty->print_cr("  Nearing GC overhead limit, "

"will be clearing all SoftReference");

}

}

}

}

// Set this even when the overhead limit will not

// cause an out-of-memory.  Diagnostic message indicating

// that the overhead limit is being exceeded is sometimes

// printed.

print_gc_overhead_limit_would_be_exceeded = true;

} else {

// Did not exceed overhead limits

reset_gc_overhead_limit_count();

}

}