After the change of WT-4571, there was weird performance degradation in update-only-btree wtperf found when using high number of threads (on high performance instances like i3.metal).

When we enabled diagnostic to build, we usually expected to have better performance, but in this case, the opposite situation occurs. On i3.metal instance, more than 10% performance degraded in 32 threads and 128 threads. (weird that it is improved in 64 threads)

More related results can be found on this Jira comments: https://jira.mongodb.org/browse/WT-4571?focusedCommentId=2170548&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-2170548