On Wed, 2008-11-26 at 11:46 -0600, Tim Chase wrote: > > I am currently attempting to roll my own multiple database > > support for django for a new project. I have attempted to > > search for examples of this but have not found very much. > > Does anyone have some examples on how I can accomplish this? > > > There are multiple facets to "multiple database" usage > scenarios...which are you looking for? > > 1) federation: "I've got data in multiple database sources and I > want my Django app to pull from all of them to give a unified view" > > 2) load balancing A: "I've got one database, but have replicated > it master-master, and I want my Django instances to spread the > load across these databases" > > 3) load balancing B: "I've got one database, but have replicated > it master-slave, and I want all my reads to go to the slave DBs, > and all my writes to go to the master DB"
By the way, Tim, unless you're using something like Oracle's gigabit-speed replication or synchronous replication, this last one is almost always "all reads to go to the slave DB, unless they're related to a recent write, in which case they should go to the master". Asynchronous replication (e.g. MySQL's master-slace situation) has a lag between between writes and when they appear in the slave. The lag can be seconds. For example, when Pownce were setting up this type of replication, they had to be very careful to ensure that after you posted a note, the reads to display the page came from the master so that the note actually showed up (people tend to get worried when they post something and it doesn't appear). Ditto for comments, etc. It took a day or so of fairly intensive work, tracing through possibilities to get that mostly working for all cases of "reads associated with a recent write". This case, (3), is one or the more common and perceived as an easy way to balance load, but it has those sorts of hidden traps that need to be avoided. Your summary is still spot-on, though, and people talking about "multiple databases" definitely need to be clear as to which situation they're talking about (and, when it involves replication, whether it's synchronous or asynchronous -- although it's almost always the latter). Regards, Malcolm --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
