On Nov 8, 2008, at 3:07 PM, Mike Bernson wrote:
>
> I am looking at how to have 2 engines a session.
>
> I want to be able to switch between engine used based on
> if any writes will be happening to the data being read. I
> can tell if any data will be modify by if the transaction
> started by issues a begin.
>
> I want to setup a number of server doing Replication. I need
> to have a master and a number of slaves.
>
> In the code I always start transaction that will be doing write with
> begin. I would like to
> have the session have 2 engines. The first engine is used outside of
> any transaction that
> have not started with a begin. This would allow all reads to use a
> slave mysql server and
> keep the records in the session identify map. The second engine
> would be used for writes.
> This engine is selected in the transaction started with a begin. The
> rows are read with
> select for update. These rows also would be session identify map.
> When flushing modified
> data it need to be flushed to master.
set session.bind = <any engine> as needed. I recommend a decorator
for the general use case, such as
@decorator
def with_master(fn, *arg, **kw):
sess = Session()
sess.bind = the_master
try:
r = fn(*arg, **kw)
finally:
sess.bind = not_the_master
return r
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