Security Update 2019-005 causes slowdown

[bootsydan]

Hi all,
I'm on 15" macbook pro, mid 2012.
Sierra 10.12.6

Since recently installing the security update 2019-005 my mac has been incredibly slow. The slowness occurs at startup (takes 10 minutes or so to load dock/top panel/desktop and become useable), when accessing top panel (after clicking apple logo and 'about this mac' it takes thirty seconds or more for the dialog box to appear), opening apps, and opening multiple tabs in web browser. For the last 25 minutes or so I have done only basic web browsing, and opened one excel file. My memory usage says:
*memory used: 3.43 gb (out of 4 gb), cached files 570.9 mb, swap used 213.3 mb, app memory 1.02 gb, wired memory 1.06 gb, compressed 1.31 gb. kernel_task 558 mb and Firefox are the only things taking up >100 mb memory.
*cpu usage: system < 5%, user <5%.
*disk: mds_stores 4.3 gb, kernel_task 1000 mb, launchd 660.3 mb, firefox 233 mb, and all the rest minimal.

I have reset SMC, PRAM and run CleanMyMac X (including system scan, optimisation and maintenance). None of this has helped. Before this, everything was running quite smoothly.

I did have one hiccup about a month ago. Back then I was on High Sierra. I tried to boot with power disconnected and low battery, and battery must have died before boot completed, as it failed. To get it to work again I had to reset SMC and PRAM, but it was incredibly slow - the same as it is now - and the only thing that fixed it was reinstalling the native OS that came with the laptop - Sierra, which is what I use now. Since reinstalling Sierra I haven't had any further problems.... until installing this update. I would much prefer to find a solution than to reinstall the OS over again. Any ideas, things to try, are much appreciated.

 

[KeesMacPro]

IMO there are lots of things to consider/ possible causes for this issue:

-if non-retina MBP 2012 the drive could be a HDD which is very slow , an SSD e.g. Samsung 860 EVO will improve boot time and general performance a lot
-4GB RAM is far from sufficient so the OS starts swapping data RAM> disk. Result: further slowdown;I'd install 2x8GB or 2x4GB minimum.
Looks like the CPU is not only paging RAM to disk, but also compressing it which means that the 1GB on the disk is still not enough ;resulting in even more slowdown.
-If your MBP is a retina, 1 RAM module is defective/ not inserted properly , as the retina was shipped with 2x4GB min
-booting with power failure very likely corrupted the OS and/or data
-the drive could be failing ( DriveDX is a very good tool for this)
-there's (almost) no free space left on the drive
-the MBP 2012 non-retina is known for failing SATA flex cables , especially the 13 inch, but I wouldnt exclude the 15 inch: replacement SATA cable upgrade is not expensive and easy to perform
-CleanMyMac is absolute garbage and IMHO does more damage than solving anything
-mds_stores means Spotlight is indexing > further slowdown , question is why this occurs : new data e.g.photos/ fresh data migration?
open terminal and run: sudo mdutil -a -i off
This turns off indexing.
To turn on again: sudo mdutil -a -i on
-although you prefer to "find a solution" instead of reinstalling the OS , IMO this is the first step to find out if it's a hardware or software issue: If the issue is still present with a clean install it's hardware related .

Apart from afore mentioned , a fresh install on an erased drive of e.g. Sierra, High Sierra or Mojave should boot up in ~ 20 sec from an SSD....
Personally I'd install Mojave (one of the most stable OSes) or High Sierra .
Assuming a fresh install runs stable and smooth, it's easy to recover your data with Migration Assistant from a backup.