Elasticsearch GC 時間過長的解決方法

前言：GC 時間過長是個常見的問題，下文我將對應的現象和解決方案進行闡述。爲何這麼解決，能夠參考個人另一個博客中的內存使用和GC指標這個章節

咱們有時會發現elasticsearch集羣掛掉，或者有點數據節點脫離集羣，這裏有多是GC方面的緣由，實質是內存的緣由。

1、日誌表現

[2017-06-22 23:56:51,008][WARN ][monitor.jvm              ] [data-vm0] [gc][old][5214195][124260] duration [22.4s], collections [1]/[23s], total [22.4s]/[4.2d], memory [13gb]->[13gb]/[13.6gb], all_pools {[young] [21.7mb]->[25.2mb]/[532.5mb]}{[survivor] [0b]->[0b]/[66.5mb]}{[old] [13gb]->[13gb]/[13gb]}
[2017-06-22 23:57:21,419][WARN ][monitor.jvm              ] [data-vm0] [gc][old][5214196][124261] duration [29.6s], collections [1]/[30.4s], total [29.6s]/[4.2d], memory [13gb]->[13gb]/[13.6gb], all_pools {[young] [25.2mb]->[32.7mb]/[532.5mb]}{[survivor] [0b]->[0b]/[66.5mb]}{[old] [13gb]->[13gb]/[13gb]}
[2017-06-22 23:57:43,963][WARN ][monitor.jvm              ] [data-vm0] [gc][old][5214197][124262] duration [22.3s], collections [1]/[22.5s], total [22.3s]/[4.2d], memory [13gb]->[12.9gb]/[13.6gb], all_pools {[young] [32.7mb]->[19.4mb]/[532.5mb]}{[survivor] [0b]->[0b]/[66.5mb]}{[old] [13gb]->[12.9gb]/[13gb]}
[2017-06-22 23:58:14,390][WARN ][monitor.jvm              ] [data-vm0] [gc][old][5214198][124263] duration [30.1s], collections [1]/[30.4s], total [30.1s]/[4.2d], memory [12.9gb]->[13gb]/[13.6gb], all_pools {[young] [19.4mb]->[28.5mb]/[532.5mb]}{[survivor] [0b]->[0b]/[66.5mb]}{[old] [12.9gb]->[13gb]/[13gb]}
[2017-06-22 23:58:37,356][WARN ][monitor.jvm              ] [data-vm0] [gc][old][5214199][124264] duration [22.5s], collections [1]/[22.9s], total [22.5s]/[4.2d], memory [13gb]->[13gb]/[13.6gb], all_pools {[young] [28.5mb]->[9.9mb]/[532.5mb]}{[survivor] [0b]->[0b]/[66.5mb]}{[old] [13gb]->[13gb]/[13gb]}
[2017-06-22 23:59:07,774][WARN ][monitor.jvm              ] [data-vm0] [gc][old][5214200][124265] duration [29.9s], collections [1]/[30.4s], total [29.9s]/[4.2d], memory [13gb]->[13gb]/[13.6gb], all_pools {[young] [9.9mb]->[1.3mb]/[532.5mb]}{[survivor] [0b]->[0b]/[66.5mb]}{[old] [13gb]->[13gb]/[13gb]}
[2017-06-22 23:59:40,430][WARN ][monitor.jvm              ] [data-vm0] [gc][old][5214205][124266] duration [27.6s], collections [1]/[28.6s], total [27.6s]/[4.2d], memory [13.5gb]->[13gb]/[13.6gb], all_pools {[young] [515.7mb]->[73.7mb]/[532.5mb]}{[survivor] [0b]->[0b]/[66.5mb]}{[old] [13gb]->[13gb]/[13gb]}

2、解決辦法

出現上述狀況的日誌，說明節點正在承受內存方面的壓力。

1.增長節點的內存,縱向分擔壓力（%50的RAM 並不大於32G）
2.增長節點數量，橫向分擔壓力

NOTE: 可能有些小夥伴會清理caches來減輕壓力。我認爲此處清理cache是無論用的，由於下次查詢的時候 fielddata 會被reload。