Revert the wal_dir back

[killme2008]

What type of enhancement is this?

Configuration

What does the enhancement do?

It was removed in f71aa37

But it's helpful when you have different disks for wal and data, so let's add it back.

Implementation challenges

No response

[shoothzj]

I am interested in this change. Could you please assign this to me?

[killme2008]

I am interested in this change. Could you please assign this to me?

Cool, it's yours.

[tisonkun]

@killme2008 I noticed that now we use these three consts for different dir:

/// WAL dir for local file storage
pub const WAL_DIR: &str = "wal/";

/// Data dir for table engines
pub const DATA_DIR: &str = "data/";

/// Cluster state dir
pub const CLUSTER_DIR: &str = "cluster/";

Does this issue mean to use a configurable or at least variable wal_dir to replace the const? What for the rest two?

Besides, this seems be closed by d9e7b89.

[tisonkun]

The three consts seem default value.

[killme2008]

@tisonkun Looks like it was fixed via #2606

Thank you. You can find other issues if you are interested.