Jonas Oreland wrote:Daniel Ek wrote:
I today have a database using 20GB storage, which actually means that I should have at least 30GB (40GB recommended) ram using Mysql cluster.
This could be 40 boxes with 1G ram each.
But doesn't that increase the locking conflicts significantly? It is my understanding that 2PC locking conflicts scale with the third power of the number of nodes:
http://citeseer.ist.psu.edu/gray96danger.html
Btw: We're also working on adding "disk data", i.e. data that does
not have to reside in ram all the time. This will however probably not be finished until the end of this year.
How about a synchronous transaction log? 99.999% availability is nice for the PHB, but my concern is what happens when the 0.001% hits the fan, the whole cluster goes down and the transaction log has not yet been written to disk.
Does MySQL Cluster meet the D of ACID?
1 ) Just curious; e.g a power failure if the whole database resides in RAM wouldn't that mean data loss for the data that resides in the RAM or does the NBD engine "simply" add duplicate data on at least one node? If I have 40 nodes and a 20GB database would that mean that 1/20 would actually reside on 2 physical nodes and so on?
Yes. So you would probably need more like 60 systems with 1 GB RAM each for a 20 GB dataset + overhead + space to grow. Or 8 machines with 8 GB each to keep it manageable, reduce the locking issues and be able to fit it in one rack.
Jochem
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