Description:
All index builds in 4.2 now run in the background by default. The server will ignore
Unknown macro: { background}
index specifications, unless the setParameter enableHybrid IndexBuilds=false is used. Performance is comparable to foreground index builds, but now writes can be accepted during the build process and applied at the end. Look for the "index build: starting on ... using method: Hybrid" log message when an index build starts. The log message "index build: drain applied X side writes", which indicates that background writes received during the index build are being applied.
Engineering Ticket Description:
This work will cause the background:true index option to be ignored, thus making all index builds run through the new hybrid index build path.