[database-devel] Multi-threaded access to an SQLite database

[Leon Smith]

As quick and easy workaround,  you could use a single haskell thread
to talk to SQLite,  and then snaplet-sqlite-simple code would then
talk to this thread instead of issuing sqlite-simple calls directly.
I've done the same thing to interface with zeromq,  using my
split-channel library.

Leon

On Fri, Jan 4, 2013 at 5:54 PM, Janne Hellsten <jjhellst at gmail.com> wrote:
> Moving the discussion over to database-devel - others may find this
> interesting / may have run into this.
>
> FWIW - I also tried setting up a test case which would have multiple
> concurrent writers, but couldn't get this to fail.  I suspect though
> that my test case wasn't good enough to hit this problem.
>
> Background: This originated from [1], also collected some notes on [2].
>
>   [1]: https://github.com/nurpax/snaplet-sqlite-simple/issues/5
>   [2]: here: http://nurpax.github.com/posts/2013-01-04-note-to-self.html
>
> Janne
>
>
> On Sat, Jan 5, 2013 at 12:38 AM, Joey Adams <joeyadams3.14159 at gmail.com> wrote:
>> On Fri, Jan 4, 2013 at 4:43 PM, Janne Hellsten <jjhellst at gmail.com> wrote:
>>>
>>> I was just wondering if you have any past experience on multi-threaded
>>> use of SQLite?  I hit some issues last week, started seeing
>>> SQLITE_BUSY on inserts and wasn't quite sure what to think about it.
>>> I wrote some notes about it here
>>> http://nurpax.github.com/posts/2013-01-04-note-to-self.html.  Have you
>>> by any chance had to deal with such problems before?
>>
>>
>> According to the SQLite FAQ [1], only one writer can access the database at
>> a time.  I haven't run into this myself, though.
>>
>> Be careful with transactions.  If you allow multiple threads to access a
>> database handle, and to issue BEGIN/COMMIT on their own terms, then one
>> thread might issue BEGIN and interfere with other transactions.  Thus, make
>> sure the MVar lock is held for the duration of the transaction.
>>
>> PS: Mind CCing this to database-devel at haskell.org ?
>>
>>  [1]: http://www.sqlite.org/faq.html#q5
>
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