[Dovecot] Avoiding Hardlinks (was: Something other than dotlock for uidlist locking?)
tss at iki.fi
Thu Aug 10 01:05:01 EEST 2006
On 9.8.2006, at 23.44, James Berry wrote:
> In seaching the code for "link(", I find only four affected files/
> cases. Here I look into possible implementations for a patch to
> AVOID_HARDLINKS. Such a patch would dramatically improve
> performance on Mac OS X with the HFS+ filesystem.
Hmh. The only annoying problem with this is that it should be runtime
configurable, but there's no clean way to do that without larger
> Timo, would you mind commenting on these to make sure my
> understanding is correct? And for the last one, I need a suggestion
> on how to proceed.
> file-copy.c: [EASY]
> Looks like it would be easy to take the already coded case for
> when try_hardlink is false.
Yes, easy. This case could even be #ifdefed. Although currently the
only user of file_copy() is copying ssl-parameters.dat from /var/lib/
dovecot to /var/run/dovecot, and I don't see it being used elsewhere
> file-dotlock.c: [EASY]
> In dotlock_create, use try_create_lock_excl rather than
This really should rather be configurable from dovecot.conf, but
there's no simple way to do that, except something like a getenv()
hack inside the file-dotlock.c code..
I don't think this should be #ifdefed since O_EXCL could break if
you're using NFS.
> maildir-copy.c: [LOOKS EASY]
> In maildir_copy(), take the fallback case using mail_storage_copy.
This is the default (maildir_copy_with_hardlinks=no) so no need to do
> maildir-save.c: [NEED HELP]
> In maildir_file_move(), there seems to be no fallback case, and
> I'm unsure of the desired symantics, so I could use some
> suggestions here: can we just fall back into something like the
> code in file-copy.c?
Like you noticed, this can be changed to just rename(). The only
reason it's link()+unlink() is because maildir spec says it should be
done like that. And in case the maildir filenames aren't really
unique the link()+unlink() method makes sure that mails aren't
overwritten, but that practically can't happen with Dovecot. This
code could perhaps also be #ifdefed..
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