I just came here to post that Spotlight is going nuts on 1.7.4 under 10.13 as well and see if anyone else had seen anything
. It was always somewhat unreliable, but it would at least work much of the time and index for a while then stop. Since upgrading though I've seen it run constantly, with mds and mds_store pegging a few cores, mds_store consuming ever increasing amounts of memory (I just killed it again, it had reached over 64 GB and heavily slowed down the system of course). As soon as I kill them they restart, and mds_store is increasing real and private mem usage by at least 10-20 megs a minute. I haven't tried blowing away all indexes or anything yet, but this is definitely new behavior regardless. I've got my main user folder on native ZFS and Mail.app is always a good test case of whether Spotlight is functioning properly since it depends on it for searches and smart folders and the like, it used to work intermittently at least but not at all since 1.7.4.
At any rate I don't think it's just a Mojave problem. I'm going to restart and try clearing indexes on all the ZFS volumes to see what happens. Happy to provide any details on pool config that might be relevant. Right now on this system I'm not using HFS formatted ZVOLs at all, blew them all away during a previous upgrade, so it's just right on ZFS. I might try at least one to see if it fixes odd compile/build problems with MacPorts though.