Visar, HiLo is not magic. The assertion "Whenever the counter reaches max_lo, it fetches a new Hi value from the DB." applies to a LIVE APPLICATION INSTANCE / SessionFactory. The first time an id needs to be generated in a session factory, a new Hi value is fetched. Also, read Tuna's post. If you want to "preserve" all your key space (I can't think why. Are 64-bit integers expensive in your country?), use identity.
Diego On Sat, Apr 3, 2010 at 08:51, Visar Uruqi <visar.ur...@gmail.com> wrote: > Hello Diego > > Thank you very much for your detailed explanation > I did some tests and found out many things about the hilo > implementation in nhibernate, > > I have a question regarding the lo value the so called "counter" > You said "Whenever the counter reaches max_lo, it fetches a new Hi > value from the DB." > > Well After I restart my application the counter doesn't continue where > it left, instead > it inserts a new "next_hi" value specifically it increment's the > "next_hi" value in DB, > whereby it wastes many id's, what I'm trying to say, the counter > doesn't reach > necessarily the max_lo, after application restart it fetches a new Hi. > > Is there a way to preserve the counter, so if it doesn't reach the > max_lo, it should > continue where it left on the next start of application and not insert > a new nex_hi value > and whereby waste a whole range of keys? Is there a possibility to > continue where it left? > > Visar > > > On Mar 31, 11:25 pm, Diego Mijelshon <di...@mijelshon.com.ar> wrote: > > Read the post carefully. The second formula is how to determine the value > to > > insert as the initial "next_hi" when migrating from identity. > > > > You can see exactly how the IDs are generated here: > https://nhibernate.svn.sourceforge.net/svnroot/nhibernate/trunk/nhibe... > > . > > They are not random, they are sequential. > > > > And yes, you can potentially run out ofhi numbers. To avoid it, you need > > to: > > - Use long enough Id columns (32 or 64 bits depending on the usage) > > - Adjust the max_lo value to reduce the "wasted" key space when > application > > instances generate much less values than the default (this applies mostly > to > > desktop applications) > > > > Diego > > > > > > > > On Wed, Mar 31, 2010 at 17:36, Visar Uruqi <visar.ur...@gmail.com> > wrote: > > > Thank you very much Diego for your reply. > > > > > I found the following formulas in this link > > > > >http://stackoverflow.com/questions/1390078/is-there-a-practical-way-o. > .. > > > > > hilo-id = high-value * max_lo + low-value > > > > > high-value = ceiling(current-identity / max-lo) > > > > > Can you check if they are ok? Is the hilo-id really by this > > > formulas generated? > > > > > How is the lo-value generated in the clients computer? Randomly? > > > > > Is it true that all numbers might get exhausted? > > > > > Visar > > > > > On Mar 31, 3:58 pm, Diego Mijelshon <di...@mijelshon.com.ar> wrote: > > > > There aren't many steps... it's pretty simple... I'll try to address > your > > > > questions. > > > > > > I did not understood this part "Don’t use this generator with a user- > > > > > > supplied connection". > > > > > > Anybody know what he meant with this? > > > > > > ISessionFactory.OpenSession has overloads that take an IDbConnection. > > > > If you use them, you can't use HiLo, because it needs the > SessionFactory > > > to > > > > be managing connections. > > > > It's an implementation detail, but basically, the hi values are > retrieved > > > in > > > > a separate transaction, as they are SessionFactory-wide and > indepentent > > > of > > > > the Session-initiated transaction. > > > > > > I tried the hilo and it generates a table with the name > > > > > > "hibernate_unique_key" and one > > > > > > column "next_hi" > > > > > > Those are actually configurable. It might help thinking of that table > > > with a > > > > single column and record as a replacement for sequences in databases > that > > > > don't support them. When you use seqhilo, all you have is a sequence > > > name. > > > > > > It also generates high values for ID's like 32772 > > > > > > I would like to understand this in depth, what are they for? > > > > > > The HiLo algorithm is pretty straightforward. > > > > Each identifier is composed by two parts, a Hi value that comes from > the > > > DB, > > > > and a Lo value that is generated locally (an incrementing counter) > > > > The Id is generating by combining those two parts, based on the > max_lo > > > > parameter, which specifies how many values you can generate for each > Hi > > > > value retrieved from the DB. > > > > The default max_lo is 32767, which means the lower 15 bits would be > used > > > for > > > > Lo values (that's why a value like 32772 is generated in the first > > > > transaction). > > > > Whenever the counter reaches max_lo, it fetches a new Hi value from > the > > > DB. > > > > > > For the implications of the HiLo behavior, I recommend this post by > > > Fabio: > > >http://fabiomaulo.blogspot.com/2009/02/nh210-generators-behavior-expl. > .. > > > > > > Diego > > > > > > On Wed, Mar 31, 2010 at 10:10, Visar Uruqi <visar.ur...@gmail.com> > > > wrote: > > > > > Hello > > > > > > > Is there a step by step using hilo article? > > > > > > > I found out that in order to take advantage of batch commands in > > > > > nhibernate > > > > > you have to use hile generator (<generator class="hilo" />) > > > > > I looked at Nh Doc and Nh in Action, it does not say much about it, > > > > > I've came accross this statement: > > > > > > > "Generates identifiers that are unique only for a particular > database. > > > > > A high/low algorithm > > > > > is an efficient way to generate identifiers of any integral type, > > > > > given a table and > > > > > column (by default hibernate_unique_key and next_hi, respectively) > as > > > > > a source of hi > > > > > values. See (Ambler 2002) for more information about the high/low > > > > > approach to unique > > > > > identifiers. Don’t use this generator with a user-supplied > > > > > connection." > > > > > > > I did not understood this part "Don’t use this generator with a > user- > > > > > supplied connection". > > > > > Anybody know what he meant with this? > > > > > > > I tried the hilo and it generates a table with the name > > > > > "hibernate_unique_key" and one > > > > > column "next_hi", It also generates high values for ID's like 32772 > > > > > I would like to understand this in depth, what are they for? > > > > > If anybody knows a link that explains much in detail about hilo? > > > > > I'm very curious to know about this. > > > > > > > Visar > > > > > > > -- > > > > > You received this message because you are subscribed to the Google > > > Groups > > > > > "nhusers" group. > > > > > To post to this group, send email to nhus...@googlegroups.com. > > > > > To unsubscribe from this group, send email to > > > > > nhusers+unsubscr...@googlegroups.com<nhusers%2bunsubscr...@googlegroups.com> > <nhusers%2bunsubscr...@googlegroups.com<nhusers%252bunsubscr...@googlegroups.com>> > > > <nhusers%2bunsubscr...@googlegroups.com<nhusers%252bunsubscr...@googlegroups.com> > <nhusers%252bunsubscr...@googlegroup s.com>> > > > > > . > > > > > 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 nhus...@googlegroups.com. > > > To unsubscribe from this group, send email to > > > nhusers+unsubscr...@googlegroups.com<nhusers%2bunsubscr...@googlegroups.com> > <nhusers%2bunsubscr...@googlegroups.com<nhusers%252bunsubscr...@googlegroups.com>> > > > . > > > 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 nhus...@googlegroups.com. > To unsubscribe from this group, send email to > nhusers+unsubscr...@googlegroups.com<nhusers%2bunsubscr...@googlegroups.com> > . > 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. 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