Can't say anything about shaders but I do know a thing or two about database queries:
1. Queries are often repeated, i.e. most of backend DBs get the same requests over and over again. Even a slow jit compiler is fine here as things just get cached.
2. Queries usually take some time to complete, and this offsets the jit-related latency.
Also, Postgres has a very limited kind of jit compilation, i.e. for expressions only.
Notice that javascript jit compilers usually have a multi-tiered compilation. That's because proper compilation takes time, and sometimes it is more efficient to just do some basic template jiting (or no additional compilation) instead of firing the heavy guns.
1. Queries are often repeated, i.e. most of backend DBs get the same requests over and over again. Even a slow jit compiler is fine here as things just get cached. 2. Queries usually take some time to complete, and this offsets the jit-related latency.
Also, Postgres has a very limited kind of jit compilation, i.e. for expressions only.
Notice that javascript jit compilers usually have a multi-tiered compilation. That's because proper compilation takes time, and sometimes it is more efficient to just do some basic template jiting (or no additional compilation) instead of firing the heavy guns.
None of them use LLVM, btw.