Oohh. I love when explanations like this contains bits of history about the project. As well as the sense of humour in some of our logging messages :) https://github.com/apache/jena/blob/7b011c30b6bf54db44b5b14408f103009adbdd67/jena-core/src/main/java/org/apache/jena/shared/uuid/JenaUUID.java#L193
Thanks Andy! Bruno On Sun, 12 Aug 2018 at 8:50, Andy Seaborne ><a...@apache.org> wrote: >JenaUUID predates UUID. > >Yep - it is really old. > >V1 UUIDs used to be the more encouraged form ... nowadays they aren't - >they don't even work really. > >Why? devices don't have a guaranteed 48 bit address or anything else to >seed the device unique part. > >Fine, when everything was a computer with network hadware. >Then came the desire to have them on small devices, not, connected >devices, and then on VMs. No reliable unique 48bit number. > >I don't think the guessablity of the next id was much of an issue. > >Generating V1 ids requires synchronization or batch allocation; V4 can >be generated in parallel. > >JenaUUID, originally called JUUID, came about to have URNs-style ids but >also to write down the details of UUIDs. > >Today, maybe it would be a library of static functions to add >functionality around UUIDs, especially producing URI strings. > >They are both objects which are a pair of longs. > >V1 UUIDs are easier to debug if there are several around - the numbers >move up incrementally. > > Andy > > > > >On 11/08/18 10:47, Bruno P. Kinoshita wrote: >> Hi! >> >> >> Regarding changes in Jena code, not talking about SPARQL uuid or struuid >> functions... Does anyone here know when one would use Java's UUID in Jena >> over JenaUUID implementations, or vice versa? >> >> >> I wrote one of those brain-dump posts, with several notes to myself, about >> what happens when you upload a dataset in Fuseki. Ended up with a post-it to >> check out JenaUUID. >> >> Today I had some spare time, and tried learning how it works [1], from what >> I understood, we have a Version 1 (UUID_V1) and a Version 4 UUID (UUID_V4) >> implementations in Jena, where version 4 is compatible with Java's UUID (but >> with a stronger seed for multiple JVM's?). >> >> But in certain parts of the code we use Java's UUID. The transaction ID's >> are either sequential or JenaUUID. But blank node ID's are either sequential >> or Java's UUID. >> >> Just so I learn (and satisfy my curiosity), in case I ever have to touch >> code that involves UUID's in Jena... is there a rule for when to choose one >> over the other? >> >> Thank you! >> Bruno >> >> [1] https://kinoshita.eti.br/2018/08/11/uuids-in-apache-jena/ >> >
