More testing. I repeated my prior test on the LAN but this time using Network Link Conditioner to add artificial 1 through 10 msec delays (on each direction, so 2 through 20msec total ping).
I also did the same test run using PSoS (Perform Script on Server) which presumably has close to zero latency.
Results:
PSoS: 10 seconds
Localhost (0.1 msec ping): 35 seconds
LAN (0.7 msec ping): 38 seconds
LAN (2 msec ping): 82 seconds
LAN (5 msec ping): 161 seconds
LAN (10 msec ping): 218 seconds
LAN (20 msec ping): 557 seconds
Conclusion: latency in FileMaker is an absolute killer.
Here's a graph of the results:
This graph suggests the raw processing takes about 15 seconds, and the rest is network latency, with each millisecond of latency adding about 25 seconds to the total time.