Note: Backup Breakpoints were based on DBUG_SYNC_POINT. They were part of the MySQL code in some early 6.0 versions. Backup Breakpoints have been removed from the code in favor of the Debug Sync Facility.
open_tables(...) BACKUP_BREAKPOINT("bp_after_open_tables"); lock_tables(...)
The BACKUP_BREAKPOINT macro consists basically of:
DBUG_EXECUTE_IF("backup_debug", DBUG_SYNC_POINT((S), 300))
Opportunities and downsides of the DBUG_SYNC_POINT method apply here too.
In addition we had the downside that DBUG tracing was hampered as explained in the "Dbug Sleep" section.