On May 6, 3:43 am, Ants Aasma <ants.aa...@gmail.com> wrote:
> On May 6, 9:07 am, Vic <vctr...@gmail.com> wrote:
>
> > I'm looking for a way to have my DB replicated in REAL TIME to be used
> > in case I lose my primary copy.
>
> > I saw that the two phase commit exist but I'm not sure if that is the
> > correct option. I have the feeling that it would be abusing a
> > mechanism purposed for correlating to separate DBs and not creating
> > replications.
>
> The preferred way to replicate databases is to use ready-made database
> replication tools. For postgres the easiest way to do synchronous
> replication is currently pgpool-II. With mysql I'm not so sure,
MySQL has a mechanism for a database to read the log from a master
database and replay the commands. This provides a loose coupling with
near real-time backup of the data. Should the backup server stop or
lose contact, the primary server is unaffected. When the backup
server regains contact, it restarts the log processing from the point
where it left off.
there
> is the NDB cluster, but it has its own issues, possibly you can find
> similar replication middleware for it.
>
> If you must do the replication inside your application, then my advice
> is to do it by subclassing sqlalchemy.engine.{Engine,Connection} to
> handle distributing requests to multiple backends and managing
> transactions across them. You still need 2 phase commits to achieve
> consistency, and the corresponding separate transaction management
> that goes with it (to rollback/commit prepared transactions in case of
> crashes). Also to avoid inconsitencies you have to get sequence values
> from one database, and cannot use volatile functions for inserts,
> updates. Also, if you are doing this to get high availability, then
> you need figure out, how to bring a replica up online. Don't expect
> this to be anything near simple or transparent if you want to have any
> kind of concurrency for write queries.
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