postgres: Document socket length limitation and workaround

[srid]

#77

[srid]

We may want to have a separate page, guide/datadir.md, first and then talk about this. Then we can link to it from postgresql.md.

[srid]

Also, is $HOME the best place? Why not $TMPDIR (falling back to /tmp)?

[shivaraj-bh]

on darwin TMPDIR seems to be set, but that’s not the case in my NixOS. Not sure how it is in other linux distros. Perhaps if this is not set, we can fallback to /tmp.

[shivaraj-bh]

We may want to have a separate page, guide/datadir.md, first and then talk about this. Then we can link to it from postgresql.md.

#144

[shivaraj-bh]

postgres doc mentioning the socket length limitation: #147

[shivaraj-bh]

Also, is $HOME the best place? Why not $TMPDIR (falling back to /tmp)?

This might not be as straight forward as it seems. Let’s assume that the socketDir option is set to “$TMPDIR/”, we can check for the presence of $TMPDIR in the shell script, but how do we then propagate the final socketDir path (after fallback to /tmp), to the settings option?

[srid]

What happens if we don't set this option in the first place? What is postgres' default -- and is that sufficient?

services-flake/nix/postgres/default.nix

Line 201 in 18f9dec

unix_socket_directories = lib.mkDefault config.socketDir;

[shivaraj-bh]

What happens if we don't set this option in the first place? What is postgres' default -- and is that sufficient?

services-flake/nix/postgres/default.nix

Line 201 in 18f9dec

unix_socket_directories = lib.mkDefault config.socketDir;

It will use dataDir by default

[srid]

The default value is normally /tmp, but that can be changed at build time.

https://www.postgresql.org/docs/current/runtime-config-connection.html

So, the nixpkgs package uses something else as default?

Also, it looks like we can disable this entirely:

An empty value specifies not listening on any Unix-domain sockets, in which case only TCP/IP sockets can be used to connect to the server.

(Will that break anything in CI though?)

[shivaraj-bh]

I was looking to disable, let me try it out.

[srid]

Due to socket path limits, the DEVENV_RUNTIME environment variable has been introduced: pointing to $XDG_RUNTIME_DIR by default and falling back to /tmp.

https://devenv.sh/blog/2023/03/20/devenv-10-rewrite-in-rust/#devenv_runtime