We recently upgraded our ELK stack from v 7.4.0 to 7.7.1 and now we noticed that the OS CPU is 100% on our hot data nodes which do the indexing. The OS CPU is almost always at 100%, the process CPU is close to 45-50%.
We checked the hot threads and saw 98% of the times it is Lucene Merging Thread. The refresh interval on our indices is 120s, size is 100gb (3 shards).
Is this a bug in 7.7.1? Or are we doing something wrong? This was not the case in previous versions.