I'm sorry, I was out of the office last week and was unable to attend this issue.
The strange thing is that the cluster doesn't seem to be under pressure. The query time is simply worse than the old version under all conditions. Maybe some tweaks related to memory vs disk usage introduced in 7.8.0 are affecting us?
Comparing your version.properties we can see the next mayor differences:
- 7.6.2 :
elasticsearch = 7.6.3 lucene = 8.4.0 bundled_jdk_vendor = adoptopenjdk bundled_jdk = 13.0.2+8
- 7.8.0 :
elasticsearch = 7.8.1 lucene = 8.5.1 bundled_jdk_vendor = adoptopenjdk bundled_jdk = 14.0.1+7
Just now I'm configuring the full cluster to use openjdk 13 instead of the bundled JDK to verify if the issue is there. I Will report here the new data.