Recently I worked with a support case from a customer. They complained that the catalog import is too slow for them, it took them 6-7 minutes to import 200 entries. Their catalog is about 50k entries, which is not particularly big, but not small neither, and with that rate, it does mean they will have to wait for days for the catalog imported. This is of course not good and I jumped in when I became available. (In the end, I like performance tuning so much that I find it hard to refuse a case like this)
I did try to import their catalog on my development machine – a relatively powerful desktop with Intel Core i7 4790 CPU, 16GB of RAM and 256GB SSD on Windows 10/.NET 4.5.2. Everything went quite well – I achieved a rate of 200 entries per 9-10 seconds, which is, IMO, more than enough. (And this is on Commerce 9, on Commerce 8 then I would suspect it’s 3-4 times slower).
After some conversations with Episerver’s developer support team, it seems that the slowdown only happens with the re-import. I tried it again with re-import. Hmm, something is wrong here. The import is much slower and it eventually stops at some points. The debugger shows that it starts quite well, even faster than a new import (200 entries per 3-4 seconds, a very recent version of Commerce made an improvement of skipping the entries which are not changed to speed up the import), but it slows down by time. Profiling does not show anything obvious, most of the time was spent with loading the MetaObject:s – which is kind of expected.
I was starring at the import tab, and wondering what can be wrong, and suddenly I realized the answer is what I was looking at: