Thanks for you feedback. I will take a look at the pessimistic listener
On Fri, Jan 10, 2014 at 2:02 PM, Michael Bayer <mike...@zzzcomputing.com>wrote: > > On Jan 10, 2014, at 1:50 PM, Sylvester Steele <sylvesterste...@gmail.com> > wrote: > > Hi, > Currently I am using the sqlalchemy engine to execute string queries only. > I do plan on using sqlalchemy more extensively (including ORM) in the near > future. > I need to add retry logic on every query, in case of some database > failures (less than ideal, but the server is a bit flaky). > > Questions: > 1. Would subclassing the Engine and overriding the execute function > achieve this? > 2. Is there a better\recommended approach? > > > technically, there’s no such operation as “retry a query” in the field of > “database failures”, assuming we’re talking about disconnects. There’s > only, “retry a transaction”. So it’s typically not so simple to build a > generic “retry query” feature - a disconnect means the whole transaction is > gone, so whatever state was already built up is gone as well. In this > regard engine.execute() is kind of hiding a lot of this in that it > begins/commits a transaction on its own, but for more substantial > applications I’d advise having your application be aware of the scope of > transactions. Especially if using the ORM, it’s pretty much a requirement > as the ORM defers/bundles CRUD operations into batches. > > Unless you never perform two queries in a row, your app will perform much > better and also will integrate correctly with transaction isolation. I > typically advise that this scope is managed in just one place, as opposed > to explicitly boilerplated throughout the application, a common antipattern. > > if you’re anticipating frequent database failures, and excepting out is > not an option, you might want to go with a “pessimistic” listener as that > described at > > http://docs.sqlalchemy.org/en/rel_0_9/core/pooling.html#disconnect-handling-pessimistic > . > > > > > Thanks > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy+unsubscr...@googlegroups.com. > > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at http://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/groups/opt_out.
