Here's my guess: All the hilo-style generators should use the same algorithm. Internally, the SequenceHiLo generator uses a sequence to ensure each sessionfactory gets its own next hi value. Therefore, the hi value must increment by one.
Thanks, Jason Dentler On Wed, Feb 2, 2011 at 3:51 PM, Nick <[email protected]> wrote: > As I understand it, the HiLo algorithm for ID generation essentially > uses this formula: > > NextID = (Hi * Lo) + (++Counter) > > Hi is stored in the database, Lo is configured as part of the entity's > mapping, and the Counter is just maintained in memory within the ID > generator. Whenever Counter exceeds Lo (as new IDs are assigned to > entities), a new Hi value is fetched, and Counter is reset. Also, all > applications creating this entity basically have to use the same Lo > value to avoid potential ID collisions, given how this formula > evaluates. > > What I don't understand is the advantage this would have over simply > storing a maximum ID as the Hi value, and incrementing it by the batch > size you expect to use (instead of by 1). You would still need to > fetch a new Hi value every time you run out of IDs, but there's no > need to coordinate the batch sizes across applications, or across > time. > > For example, if the current Hi value is 1, an application could lock > and update that to 11 (batch size = 10), thereby safely ensuring it > can safely assign IDs 1-10. Another application could lock and update > it from 11 to 101 (batch size = 90), thereby ensuring that it can > safely assign IDs 11-100. > > In either approach, locking of the Hi value in the database before > updating it is crucial. But either approach would need to do the same > number of database queries to fetch new Hi values (assuming the same > batch sizes), and a "Max ID"-style approach has the additional > flexibility of allowing the batch size to differ between applications, > or over time. > > What is the advantage of HiLo here? I feel like I must be missing > something obvious. > > -- > You received this message because you are subscribed to the Google Groups > "nhusers" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]<nhusers%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/nhusers?hl=en. > > -- You received this message because you are subscribed to the Google Groups "nhusers" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/nhusers?hl=en.
