This is needed for opening lots of file descriptors, which tends to
happen more often when using RocksDB and making lots of federation
connections at startup. The soft limit is usually 1024, and the hard
limit is usually 512000; I’ve personally seen it hit >2000.
Some distributions ship with very low defaults for thread counts; similar to
low default file descriptor limits. But unlike fd’s, thread limit is rarely
reached, though on large systems (32+ cores) shipping with defaults of
~1024 as have been observed are problematic.