Product and version:
FileMaker Server v14, v17, and most likely 15 & 16
OS and version:
OS X 10.10 (FMS14) and OS X 10.13 (FMS17)
Mac Mini, i7, 16GB RAM (FMS14)
Mac Pro, Quad Core, 32GB RAM (FMS17)
When a search takes a measurable amount of time (e.g., 5 seconds or more) simultaneous same or similar searches from two+ users cause the total time to increase 5-10x. Example: Search for person A takes 10 seconds. Search for person B takes 10 seconds. Search when both request at the same time is 50-100 seconds. Results for both users appear to complete at about the same time.
Top Call Stats shows a 10-fold increase in Total Elapsed Query (Find) rows, and this can happen even if all search criteria is within the local table. In other words, when Top Call Stats shows 5 seconds for one user request, subsequent Table-Field rows for both users will indicate around 50 seconds when simultaneous.
It is unknown if simultaneous searches on other tables (or even same table, different fields) has the same problem.
How to replicate
Large table, 250,000 (other developer tested with Windows server) to 300,000,000 rows. Best to perform a search that takes about 10 seconds per alone user to see that simultaneous searches cause both users to wait up to 10x the original timed test.
It is possible this happens with more complex searches in smaller tables, but I have not tested. My searches are fairly simple.
My tests included anywhere from three to nine find requests (single search, new requests) and could include related tables but could be all "local" indexed fields.
Workaround (if any)