On Oct 6, 9:32 am, Jay Stotz <[email protected]> wrote:
> I have a block of code that interacts with an external web service and
> writes the results of its interaction to the database. This code is
> sometimes called from within a Sequel transaction block. It is
> critical that the results of the web service interaction be committed
> to the database even if the outer transaction is rolled back.
>
> A savepoint is not an option because I want all work performed in the
> outer transaction to be rolled back in the event of an exception or
> explicit rollback at any point before or after the web service code is
> called.
>
> I got the behavior I want by running the independent transaction in a
> separate thread but I think there must be a more efficient way to do
> this. Any suggestions?
>
> def parallel_transaction(*args, &block)
> result = nil
> Thread.new { result = transaction(*args, &block) }.join
> result
> end
A separate thread is one way. The other way is to use the sharding
support with a fake server:
DB = Sequel.connect(..., :servers=>{:fake=>{}})
And use that shard in your transaction:
def parallel_transaction(*args, &block)
transaction(:server=>:fake, &block)
end
If you do that, you need to be sure that the queries in the block
passed to parallel transaction use the fake server (using
Dataset#server).
Using a separate shard probably performs better, but is a little more
work. Using a separate thread probably performs worse, but is less
work.
Jeremy
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