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Re: 673ea509e2c: MDEV-26870 --skip-symbolic-links does not disallow .isl file creation


Hi Sergei,

On Fri, Jan 21, 2022 at 10:45 AM Sergei Golubchik <serg@xxxxxxxxxxx> wrote:
> Hi, Marko,
> On Jan 21, Marko Mäkelä wrote:
> >
> > > Why InnoDB tests depend on server's symlink support?
> > > InnoDB does not use symlinks, it uses isl files.
> >
> > In https://jira.mariadb.org/browse/MDEV-26870 you suggested using
> > my_use_symdir, which I did.
> > That variable is bound to the Boolean start-up parameter symbolic_links.
> >
> > Changing InnoDB to use actual symlinks (and to stop creating
> > "databasename" directories, to be similar to other storage engines)
> > would be a file format change that could break downgrades to earlier
> > minor versions. Therefore, it is only doable in a development release.
> That's not what I meant. I was saying, --skip-symbolic-links and
> filesystem support of symbolic links are unrelated.
> If --skip-symbolic-links was not specified, a filesystem can support
> symbolic links or not support them. In the latter case, I think, InnoDB
> technically still could use DATA DIRECTORY, even if MyISAM cannot.

That is true, the InnoDB attribute DATA DIRECTORY can be technically
supported on any file system.
The ticket MDEV-26870 gradually evolved to a request for InnoDB to be
able to disable its DATA DIRECTORY feature. Quoting your comments:

> This is not what skip-symbolic-links affects. It disables DATA/INDEX DIRECTORY support. You won't be able to create tables with DATA DIRECTORY or INDEX DIRECTORY attributes.
> In other words, the server won't create symlinks. But you can, and the server will access symlinked files all right.
> But, I think, users expect skip-symbolic-links to affect isl files too. Shall we treat it as a bug?

I think that this reasoning makes sense. If you think that my way of
avoiding test failures with ./mtr --mysqld=--skip-symbolic-links is
confusing, I am open to suggestions.

Please find a revised fix at
It is a little different, in that native ALTER TABLE in InnoDB will
always retain any DATA DIRECTORY attribute while TRUNCATE will
silently discard it.

Marko Mäkelä, Lead Developer InnoDB
MariaDB Corporation