1.zookeeper集群有时候youngGC特别慢，导致zk请求堆积和处理延迟

{Heap before GC invocations=56 (full 3):
 par new generation   total 1258304K, used 1221735K [0x00000006c0000000, 0x0000000715550000, 0x0000000715550000)
  eden space 1118528K, 100% used [0x00000006c0000000, 0x0000000704450000, 0x0000000704450000)
  from space 139776K,  73% used [0x000000070ccd0000, 0x0000000713199d30, 0x0000000715550000)
  to   space 139776K,   0% used [0x0000000704450000, 0x0000000704450000, 0x000000070ccd0000)
 concurrent mark-sweep generation total 2796224K, used 50888K [0x0000000715550000, 0x00000007c0000000, 0x00000007c0000000)
 Metaspace       used 12484K, capacity 12808K, committed 13056K, reserved 1060864K
  class space    used 1354K, capacity 1456K, committed 1536K, reserved 1048576K
2019-12-22T17:05:06.891+0800: 974.563: [GC (Allocation Failure) 2019-12-22T17:05:06.891+0800: 974.563: [ParNew: 1221735K->104649K(1258304K), 1.0011243 secs] 1272623K->170081K(4054528K), 1.0012392 secs] [Times: user=27.87 sys=0.00, real=1.00 secs] 
Heap after GC invocations=57 (full 3):
 par new generation   total 1258304K, used 104649K [0x00000006c0000000, 0x0000000715550000, 0x0000000715550000)
  eden space 1118528K,   0% used [0x00000006c0000000, 0x00000006c0000000, 0x0000000704450000)
  from space 139776K,  74% used [0x0000000704450000, 0x000000070aa825c0, 0x000000070ccd0000)
  to   space 139776K,   0% used [0x000000070ccd0000, 0x000000070ccd0000, 0x0000000715550000)
 concurrent mark-sweep generation total 2796224K, used 65432K [0x0000000715550000, 0x00000007c0000000, 0x00000007c0000000)
 Metaspace       used 12484K, capacity 12808K, committed 13056K, reserved 1060864K
  class space    used 1354K, capacity 1456K, committed 1536K, reserved 1048576K
}
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