MacOS Catalina RAM usage – 2GB at boot

When the wired and active RAM pass 50% - most tasks are measurably slower. You will see increased paging activity (vm_stat 15 in the terminal - watch for page outs - they indicate some memory had to be written to slow hard drive and constant page out and page in above 10-20 per minute indicates you have a RAM starved system.)

When starved for RAM, you can buy more or do less. You might want to get a monitoring software like Activity Monitor and keep the memory indicator in your dock. The system is likely thrashing based on the time delays you report. Each of the active programs needs some memory that just got paged to disk to free up extra space for memory needed by another program. It is a bad cycle and the computer just spends time running circles rather than getting done the work you wanted.

Here is a mac with every indication of RAM pressure:

But, quitting a large app like Aperture and starting it again still has no paging and the system is very responsive. Ignore the first line after the headings in vm_stat as it's the total since boot, but do watch for pageout as you have apps that are not responsive:

mac:~ me$ vm_stat 15
Mach Virtual Memory Statistics: (page size of 4096 bytes, cache hits 0%)
  free active   spec inactive   wire   faults     copy    0fill reactive  pageins  pageout
260482  1186K  74303   275275 234520  323478K  2276158  188709K   120292   640158      482 
260689  1187K  74303   275275 234038     4117        0     3256        0        0        0 
261310  1185K  74001   275250 235835    10668       77     7115        0        4        0 
292087  1153K  74711   274313 236770    32927      972    21684        0       18        0 
521469 928347  75754   269861 235897    77208      130    63300        8       41        0 
517897 936518  75766   269215 231981    27678     2504    13059        0       22        0 
463894 987202  72076   274852 233371   126855     2712    89422        2       50        0 
223701  1180K  77834   283568 265396   589512      255   562957        1     7278        0 
205013  1186K  82765   291561 265293   389442      255   369664        0     7334        0 
201401  1173K  89671   301672 265595   495426       82   472316        1     9286        0 

However, starting about 4 of the Adobe CS4 apps can push this machine into thrashing and the slowness you describe with the apps taking 30 seconds to launch and lots of bouncing of square icons in the dock.

Here is the associated vm_stat 15 showing the problem. Look specifically at the free memory plummeting to the minimum and pagein / pageout climbing.

mac:~ me$ vm_stat 15
Mach Virtual Memory Statistics: (page size of 4096 bytes, cache hits 0%)
  free active   spec inactive   wire   faults     copy    0fill reactive  pageins  pageout
 21822  1190K   4746   585056 228411  332621K  2315577  196418K   121439   781551     1806 
 86862  1152K   5123   570803 215710   124555      932   102117        0     2086       15 
 73080  1161K   8631   571301 216607    24404      337    14931        0     1994        0 
 29655  1196K  13500   572024 219284   188966      535   112913        0     3606        0 
  1668  1208K   9616   594723 216954   174145      215   144996       16    15268      121 
  4142  1206K   5795   595393 219564   322750        0   320426        0        1        0 
  3043  1204K   3485   596990 223264   138981      136   136653        0       28        0 
  2338  1205K   2782   598556 222416   332263      321   321321        0      164       30 
  3251  1204K   2919   598770 222027    90135       82    85050        0        5        0 
  2606  1203K    212   600436 224678   114502        1   112450        0       35        0 
  1188  1200K    174   600230 228582   162660      117   157230    33127      860     9914 
 22069  1200K  27612   550547 230304    89953       38    82383     8274      159     2071 
  1910  1200K    349   600071 227976    24382        0    23465     7332        1     2985 
  1164  1201K    174   600281 228423     4940        1     4046     7087        8     2500 
 30404  1203K    186   567418 229475    16087        1    16045     8566        4     2235 

I've been researching this very question for some time, and I've come to the conclusion that while there are several so-called "solutions" offered in various places, none of them really fixes the problem or makes the symptoms go away. The best I've found is techniques that change when inactive memory is swapped, such as the use of the purge command you referred to. I believe that MacLemon is correct that swapping can be disabled only in entirety and not selectively, and so disabling the swapping of inactive memory would in practice be equivalent to disabling virtual memory altogether—which could be a workable solution on a machine with really large amounts of RAM, but is impractical on machines with a low maximum RAM capacity, such as MacBooks or Minis.

The reason that none of the ad-hoc purging solutions make the situation significantly better is that there are really only two ways to force OS X to clear inactive memory: the purge command, or forcing allocation of all free memory (and since I'm not certain what method purge uses, these two may actually be more or less the same). purge, as you mentioned, takes a non-trivial amount of time to complete. Allocating all free memory simply accelerates the process by which the contents of inactive memory would be swapped out naturally, and so still takes up the same large amount of system resources. The only advantage of either of these solutions is that they allow you to choose when the swapping occurs, so it can be done before you would be normally trying to allocate that memory to something else. Whether that is actually useful to you depends on several factors, so the simplest way to find out is to just try it.

I've been testing a few of the memory-clearing utilities out there, and I've found that for me, manually forcing inactive swap requires more active monitoring of memory levels than is practical while I'm actually working, and using a utility that automatically forces the swap when free memory drops below a certain threshold is no better than letting the OS do it on its own, as I still have no control over when the swapping will occur and my apps will SPOD. So while there is an app that will do exactly what your alternative question asks for, that doesn't actually make the situation any less painful.

Until Apple's OS development team decides that the memory management system isn't working the way it's supposed to, and they figure out a way to make it work properly, the only real solution is to identify which apps are generating the most inactive memory and stop using them. In my situation, this has meant changing web browsers. I've been testing a variety of them, and Chrome is so far the one that seems to generate the least inactive memory, probably in part because every tab and every extension runs as a separate process, allowing the OS's native memory management to treat each one separately in terms of prioritizing swapping. Safari is the worst I've tried; starting with Safari 5.1, I could open a few tabs, do absolutely nothing, and watch the inactive memory rise rapidly in Activity Monitor—it would easily go from <1gb inactive to >3gb inactive within about five minutes, run the swap cycle, and then do the exact same thing. (Granted, memory that is doing nothing is exactly what makes it inactive in the first place, but it shouldn't create more inactive memory than was allocated active in the first place.) Safari 6 under Mountain Lion is a bit better, but not better enough to be worth switching back. Firefox, not being based on WebKit, ought to be better about this than either Safari or Chrome, but it has its own legacy of memory management problems, including a history of memory leaks, that make it no better in practice.

What would really fix the issue is if there was an option, likely a hidden option in the OS, telling the OS to simply dump the contents of inactive memory when needed instead of swapping its contents to disk. But I don't expect Apple to ever make such an option available.