[OpenAFS] experience of SQLite on AFS

[Derrick Brashear]

On Mon, Apr 19, 2010 at 11:41 AM, Ken Dreyer <ktdreyer@ktdreyer.com> wrote:
> Thought I would add another datapoint to the discussion of SQLite on AFS.
>
> We have several Solaris 10 servers running OpenAFS client 1.4.x and
> PHP 5.2.x. We really wanted to get PHP's PDO-SQLite extension working
> with AFS. (PHP bundles SQLite 3.3.x). We anticipate that most of our
> uses would be read-only, but a few applications would need to make
> occasional INSERTs and so on.
>
> SQLite has an option in os_unix.c (SQLITE_ENABLE_LOCKING_STYLE) to
> automatically figure out the database's filesystem type and use the
> most appropriate locking mechanism for that filesystem. Adam Megacz
> wrote a patch to SQLite back in 2006 that added AFS to this list of
> filesystems SQLite could detect. I'm not certain, but I think this
> only works for OSX (Adam, correct me if I'm wrong :-)
>
> Additionally, SQLite also has the (undocumented?) ability to define a
> fixed locking style at compile-time with SQLITE_FIXED_LOCKING_STYLE.
> This is the variable that we manipulated in our tests when we compiled
> PDO-SQLite.
>
> fnctl - Byte-range locking. Since we're using OpenAFS 1.4, this
> pretends to work but actually doesn't lock anything.
> flock - Whole-file locking. This completely hung on Solaris when
> opening sqlite files on read-only mounts. Even if the SQLite
> operations were read-only (SELECT, etc), PHP hung.
> dot-lock - did not work, as SQLite wanted to write dot-files to our
> read-only mounts.
> no locks - worked
>
> I did not expect the flock-style locking to hang when opening files
> that were mounted read-only, but it was 100% repeatable.

cmdebug output? truss output? something?

can i suggest trying it on a directory where you have rlk and not merely rl?

> We figured
> that read-access was better than nothing, so we use no locks currently
> and warn our PHP developers. We hope we can make use of byte-range
> locking some day when OpenAFS supports this on *nix.


-- 
Derrick