[Haskell-cafe] Re: HDBC-postgresql and safe/unsafe FFI calls
jgoerzen at complete.org
Fri Sep 3 20:19:37 EDT 2010
On 09/03/2010 06:14 PM, David Powell wrote:
> Hi John,
> My current usage of hdbc is in a server process that takes requests from
> multiple clients, queries the database, and returns a result. Having a
> single db query block everything else isn't really workable for me. I
> suspect this will also be an issue for others. As an example, the
> persistent-postgresql package which is part of the new Yesod web
> framework will have the same problem.
> I can send you a patch, but I am concerned with the issue Leon raised
> about libpq needing to be compiled with thread support. This is the
> default on my platforms (macosx, debian), but probably is dangerous to
> rely on. I guess we can just test the result of 'PQisthreadsafe()', in
> connectPostgreSQL and raise an error if it is false.
Or at least a warning to stderr -- that won't be a problem for
single-threaded programs, right?
> -- David
> On Fri, Sep 3, 2010 at 1:36 AM, John Goerzen <jgoerzen at complete.org
> <mailto:jgoerzen at complete.org>> wrote:
> Hi David,
> I've had varying arguments from people that want me to mark things
> safe or unsafe for various performance reasons. I'm happy to apply
> your change if you like. Can you send me a diff (and attach your
> explanation here to it, which I'll use as a commit message for
> future reference)?
> -- John
> On 09/01/2010 09:40 PM, David Powell wrote:
> I'm having an issue with the HDBC-postgresql package that
> requires me to
> manually patch it before installation for most of my use cases.
> All the FFI calls in this package are marked "unsafe".
> this means that whenever I issue a slow sql query, all other
> stops. In most places that I want to use this module, I've had to
> manually patch it to at least mark the PQexec and PQexecParams
> calls as
> Is there any reason these calls should not be marked as "safe"? I
> understand that there a little extra runtime overhead with this,
> but I'd
> have thought that negligible given all the other processing that
> goes on
> with these particular calls under the hood.
> David Powell
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