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.
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