Elasticsearch 7.9 will spend long time to forcemerge.
curl -s -XPOST http://:9200/_forcemerge?max_num_segments=1
Elasticsearch 6.2 will spend less time to forcemerge.
We have same data source on Elasticsearch 6.2 and Elasticsearch 7.9.
Forcemerging on Elasticsearch 6.2 will take 7 hours, while forcemerging on Elasticsearch 7.9 will take 16 hours.
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Are these on the exact same sorts of hardware?
Yes, they are on same hardware cluster.