We have set an elasticsearch cluster that is consisted total of 8 nodes, where 6 of them are eligible master node and data node. The rest 2 are data only node. And they are all same spec servers.
As we do performance test, we make pretty high tps (searching requests).. say, 800 tps in average for hours.
Then a master node's write IOPS spikes, which results in high load average..
I would like to know why heavy writing happens on master node much more than on data nodes.
For example, master node's IOPS hits about 50 while other nodes IOPS rarely increases to 5.