IT'S RUSSIAN HACKING!!!!
OK, seriously, I am having the same issue with a.b.teevee and a.b.moovee. Downloading 50,000 articles takes about 1.5-ish seconds, but processing collections takes anywhere from 60 to about 120 seconds. Most common seems to be about 80-90 seconds. I have also noticed that when either one of these groups is actively updating or backfilling, one of my cpus (system monitor shows 8 cpus) is always at or very near 100% utilization. My system monitor reports that the process using all the cpu is mysqld. Overall system responsiveness is also a bit off, but nothing serious. If I terminate the update or backfill, cpu and system responsiveness drop back to "normal". All of the other groups will process 50,000 articles in about 1 to 1.5 seconds and 2 seconds max, and considering the old hardware it runs great. System monitor also shows memory usage at around 2.5GB or about 15-16% and is very constant. If I never activate moovee or teevee, swap usage will be zero, but if I activate them swap usage will increase a little bit to about 110MB or 0.7% or thereabouts, but memory usage remains constant.
Just for reference, I am running Ubuntu 16.04 (fresh install btw), and using Mariadb. This is a personal installation, and I am only indexing about 30 groups, mostly small ones. At the moment, moovee and teevee are deactivated so make that 28 groups. As for hardware, an older I7-920 processor, 16GB RAM, and a 1TB Esata disk drive and there is a buttload of free space.
Wayne