Too many open files issue

[alun]

I'm running import from a blockchain DB on a MacOS machine

pbtc --btc -d /Volumes/Data/pbtc --verification-level none import /Volumes/Data/bitcoind-data/.bitcoin/blocks

I've stuck on a block 391000 with the error:

thread 'main' panicked at 'Failed to save database: "IO error: /Volumes/Data/pbtc/db/021082.sst: Too many open files"', /.../parity-bitcoin/db/src/kv/overlaydb.rs:79:9
stack backtrace:
   0: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
   1: core::fmt::write
   2: std::io::Write::write_fmt
   3: std::panicking::default_hook::{{closure}}
   4: std::panicking::default_hook
   5: std::panicking::rust_panic_with_hook
   6: rust_begin_unwind
   7: core::panicking::panic_fmt
   8: core::result::unwrap_failed
   9: core::ptr::drop_in_place
  10: alloc::sync::Arc<T>::drop_slow
  11: core::ptr::drop_in_place
  12: alloc::sync::Arc<T>::drop_slow
  13: pbtc::commands::import::import
  14: pbtc::main
  15: std::rt::lang_start::{{closure}}
  16: std::rt::lang_start_internal
  17: main

Tried to raise sysctl kern.maxfilesperproc and sysctl kern.maxfiles but this doesn't help.
Is it normal for rocks DB or this is a resource leak issue.

Side issue: is there a way to disable RockDB optimisation and run it just once after import is completed? I'm seeing it uses too much disk writes/reads as it is.