Frequently asked questions

How do I delete records from a table?

Don't do that. Seriously. Just select records you want to retain and replace original table.

I want to make my O script both executable and loadable and pass command-line parameters to it.

Use the following shebang under Linux. You need to use coreutils 8.30+ though.

#!/usr/bin/env -S bash -c 'tachyon -c 0 -f <(cat "$0" | sed "1,1d") -- $@'

Note, previously we used shebang -#!/usr/bin/env -S bash -c 'cat "$0" | sed "1,1d" | tachyon -- $@'. However, it captured stdin forever and prevented e.g. our REPL from properly working.

Now it's possible to drop into working REPL with newer shebang like:

#!/usr/bin/env -S bash -c 'tachyon -c 0 -f <(cat "$0" | sed "1,1d") -- $@'

HOME: getenv[`OPATH];
load HOME,"repl";


How can I find memory leaks in tachyon binary?

Run tachyon using $ RUSTFLAGS="-Z sanitizer=leak -Cforce-frame-pointers=yes" cargo run --bin tachyon.

To get meaningful backtraces, you must have llvm-symbolizer accessible in $PATH (LLVM 8+).

If your Linux distribution installs it prepending its version, just make a symlink like:

$ mkdir -p ~/bin; ln -s /usr/bin/llvm-symbolizer-8 ~/bin/llvm-symbolizer; export PATH=$PATH:~/bin.


How to profile / find places to improve performance?

  • For Linux, first install perf utility. For Debian-based distros (e.g. Ubuntu) execute:

$ sudo apt-get install linux-perf

  • Build tachyon with debug information by editing Cargo.toml in root of source path. Uncomment debug = true under [profile.release] section and run:

$ cargo build --release --bin tachyon

  • Prepare your test as script and run:

$ sudo perf record -g --call-graph=lbr target/release/tachyon -f script_to_profile.o
... by doing that you will record profile information which can be navigated using following:

$ sudo perf report --no-children
P.S. You should omit --call-graph=lbr in case your CPU is not Intel. That would lower profiling quality though.

Performance/network tuning

I am getting errors like "too many open files" and like that when opening many network connections. Any help?

For Linux, following limits should be increased:

  • /etc/sysctl.conf

fs.file-max = 12000000
fs.nr_open = 12000000

  • /etc/security/limits.conf

* hard nofile 12000000
* soft nofile 12000000

  • current shell

$ ulimit -n 10000000

I am getting "allocation failed ..." errors and like that when spawning lots of lambdas. What should I do?

For Linux, the following limit should be increased:


vm.max_map_count = 12000000

I am getting errors like "cannot assign requested address (os error 99)" when making many connections to a single IP. Any help?

For Linux, the following limit should be increased:


net.ipv4.ip_local_port_range = 8192 65535