Allow for separating persistent state and log directories

[dominiklohmann]

It's currently not possible to have different directories for the persistent state and the log files.

The --directory option is the only way to specify the directory for all state. Inside this dir, VAST creates a directory log that contains all ASCII logs.

This PR adds a new option named --log-directory that optionally allows setting the directory for the logs only.

[mavam]

This is useful. However, from a UX perspective I think it's weird to specify both --directory and --log-directory. More natural IMO would be to have --log-directory and --db-directory. (But both would default to --directory.)

[dominiklohmann]

I mean, speaking from a UX perspective, it is usually expected that --directory (or -C, not -d as we have it currently) sets the working directory of the binary.

Adding a separate DB directory can be done, but I'm not sure if it makes any sense.

In any case, the defaults would then have to be changed:

• system.log-directory falls back to sys.directory / vast.db / log
• system.db-directory falls back to sys.directory / vast.db

This would be not be a backwards-compatible change.

[mavam]

Just a wording nit on the changelog.

[mavam]

[..] it is usually expected that --directory (or -C, not -d as we have it currently) sets the working directory of the binary

Yeah, that actually remains the same. My point was more like that we are now starting to differentiate, maybe we'll even get --archive-directory, --index-directory, --schema-directory, and even more eventually. Because the semantics of specifying them in addition to --director is confusing (what takes precedence when all a given?), I would argue that mixing them should result in an error: either specify one top-level directory or the more granular options.

[dominiklohmann]

Let’s discuss this on Monday. I’d rather change the directory option to work like most other UNIX CLI tools have their directory option work. Especially with regards to our focus on UX.

[dominiklohmann]

@mavam I have discussed this with @0ortmann, in order to determine what the natural and expected behavior is for him from a UX standpoint. This is what we converged on:

• Drop --directory completely.
• Add --log-diretory, and --state-directory (naming tbd).
• Change the defaults: $PWD/log for system.log-directory, and $PWD/db for system.state-directory.