[jboss-dev-forums] [Design of JBoss Transaction Services] - Re: transaction support in JBossAS 5.0

[mark.little@jboss.com]

"reverbel" wrote : "mark.little at jboss.com" wrote : Yes, but in TP systems you never take a chance, no matter how small. Plus, I'm sure someone made a similar comment about date fields back in the 1960's and looks what happened come the year 2000! ;-)
  | Now your argument sounds a bit like a rhetorical one, as the year 2000 issue was an entirely different problem! ;-)
  | 

Yes and no.

anonymous wrote : 
  | Unless you use unbounded transaction ids you will be always taking a chance, which of course should be very, very, very small. Since the XA spec places an upper limit on the size of Xids, there is no way around this in the XA design space. It is really a matter of reaching a point that is safe enough.
  | 

This is interesting ;-) If we used 128 bit encoding then we could address every atom in the universe uniquely. Most schemes don't use that approach, XA being one of them. Most Uids are federated implementations, where uniqueness is guaranteed within the scope of a domain. The way XA was supposed to work was to use an approach similar to DNS, and approach a body like IANA where companies could get their own high-order bits for the Xid that would be unique to them. Then they only had to ensure that the low-order bits were unique within their own domain. Unfortunately thay didn't really take off.

anonymous wrote : 
  | Half a million years at one million TPS is certainly safe enough. Note that this would not be an upper limit on the entire lifetime of the TP system, but just on the time a transaction may remain in the active state or in a heuristically completed (and not yet forgotten) state. In other words, it is just an upper limit on the time any given transaction may exist in the current set of transaction log files. Half a million years is actually way over the top for that; a few months would probably be enough.
  | 
  | I understand "long transactions" are becoming increasingly important, but... Do you really expect them to be that long? ;-)
  | 
  | Regards,
  | 
  | Francisco

Hey, we shouldn't rule anything out ;-)

However, although I understand why you're doing this reference approach, I'm not convinced it buys you much. The size of an IOR is so large anyway when compared to an Xid, that saving a few bytes is unlikely to make much of a difference on the number of blocks that get written in the log. It's the number of physical disk blocks and not the amount of information, that makes a difference.

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