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XL has a global transaction manager, keeping the whole cluster consistent as a whole, and allows you to query the whole database for analytics, etc. BDR on the
by pgaddict 10y ago
XL has a global transaction manager, keeping the whole cluster consistent as a whole, and allows you to query the whole database for analytics, etc.
BDR on the other hand doesn't have such global component, so each node is consistent on it's own, but the nodes may be at slightly different states. Still, the replicated changes are applied transactionally (i.e. you won't see just a partial update from another node, etc.)
- gleenn 10y agoNot to offend, but "consistent on it's own" is a poor way to say "not consistent" in the way that matters.
- pgaddict 10y agoWell, if you're looking for a solution where the whole cluster is perfectly/strongly consistent, then BDR is not for you I guess. What BDR gives you is a guarantee that the changes are applied atomically (i.e. matching transactions from the source node), and in the commit order. But there's no global consistency guarantee - that's a consequence of of the asynchronous behavior.
- takeda 10y agoOver WAN you pretty much can't make things consistent. Well... I suppose you can, but it will be really slow due to speed of light.