If I understand properly the string length is there to assure easier migration. Are we sure this will work with Unicode strings which can use 2 bytes (if we were ever to use Unicode) ?
I give my +1 but I think we need to put in the M1 release notes that this Milestone is really for people that know what they are doing. Also we need to have a good testing process on existing databases. Let us know when this is commited, XWiki SAS can put some people to do a migration test of some of our wikis. Ludovic 2012/2/17 Denis Gervalle <[email protected]> > 9 days, nobody care, most of this was voted previously, I will go ahead and > commit. > Document base key format will be like: 5:space8:document > Object base key format will be like: 5:space8:document15:xspace.class[0] > > Denis > > On Wed, Feb 8, 2012 at 18:08, Denis Gervalle <[email protected]> wrote: > > > > > > > On Wed, Feb 8, 2012 at 13:43, Denis Gervalle <[email protected]> wrote: > > > >> Hi devs, > >> > >> I know this subject will seems to you already voted and discussed in > >> http://xwiki.markmail.org/thread/fsd25bvft74xwgcx > >> But following the remarks and the discussion under that thread, I had > >> largely improved the proposed changes. > >> This is an important matter, so I prefer to resume here to be sure we > all > >> really agree on this. > >> > >> To resume the current situation, we have: > >> - document id > >> - used in document table, rcs, attachment... > >> - simple 32bits string hashcode of a locally serialized > >> document reference, including the language for translated documents > >> - stored in a 64bits field. > >> - object id > >> - used in object and property tables, but also in statistics tables > >> - simple 32bits string hashcode of the concatenation of the document > >> reference, the class reference and the object number > >> - stored in a 32bits field (except in Oracle, where the mapping is > >> 32bits, but the storage is larger) > >> > >> The vote is about: > >> - document id > >> - use the lower 64bits of an MD5 hashcode > >> - the base key for the hashcode is serialized using a > >> LocalUidEntityReferenceSerializer of the document reference > >> - the result is appended with the current locale for translated > >> document, until locale are integrated in references > >> - format for original document: 5space8document > >> > > Please read: > > - format for original document: 5:space8:document > > > > > >> - format for translation: 5:space8:document2:fr > >> - object id > >> - use the lower 64bits of an MD5 hashcode > >> - the base key for the hashcode is serialized using a > >> LocalUidEntityReferenceSerializer of the BaseObjectReference > >> - current format would be: 5:space8:document12:xspace.class[0] > >> - if my proposal in the object reference thread is adopted: > >> 5:space8:document18:6:xspace5:class[0] > >> > >> Since changing document id could really not helps since document > >> reference are used in object ids and therefore unambiguous document > could > >> receive ambiguous objects, I do not advice to split the change. > Moreover, > >> this is really sensible change in the database, so not multiplying them > is > >> better. I think the upcoming 4 is a really good time to introduce this > >> change, so I propose to introduce this in version 40000 of the database > >> (4.0M1 release). > >> But I would like to use it internally earlier. So you would be pleased > to > >> settle on this thread and the previous one before. > >> > >> It implies the following migration for existing instances: > >> - customer custom mapping have to be adapted before the migration, > >> including dynamic one which could be not so easy, but this is already > >> rarely used and very rarely require any change in fact. > >> - change XWikiDocument to provide the key required for IDs, by the > way, > >> also use that key (non local version) for the document cache > >> - refactor the BaseElement hierarchy to provide long IDs (no more > >> integer) based on references (generic way to have ids for any element) > >> - change the hibernate mapping for all object ids > >> - provide dynamic schema updates using liquibase to fix all object id > >> types, including those in custom mapping and collection > >> - migrate in HQL document id for persisted > >> class: XWikiDocument, XWikiRCSNodeInfo, XWikiLink, XWikiAttachment, > DeletedAttachment > >> - migrate in HQL object id for persisted class: BaseObject, *Property, > >> internal custom mapped class, dynamic custom mapped class > >> - migrate in HQL object id for custom statistics class derived form > >> XWikiStats > >> - migrate in SQL ids for all relational collections in the above > >> migrated tables > >> > >> To provide this migration as safely as possible: > >> - Liquibase provide a safe way to change the schema > >> - All id conversion are gathered from the database in a first single > >> read-only transaction, and new id are computed. > >> - Potentially already migrated ids are detected, allowing the process > >> to fails and be restarted. > >> - Proceed to ids replacement using a safe algorithm that may support > >> non-circular conflict between old and new ids (very unlikely anyway, > since > >> we move from 32 to 64bits) > >> - Use a single transaction for each id conversion, replacing it in all > >> related tables > >> - Use Database independent queries (HQL) as much as possible, only > bulk > >> update on collection which are not supported by hibernate are in a > >> minimalistic SQL update statement. > >> > >> Some helps for testing the migration on different > >> environments is requested ! (I do my tests on MySQL deeply) > >> I will commit my branch on platform soon. > >> > >> Here is my +1. > >> > >> -- > >> Denis Gervalle > >> SOFTEC sa - CEO > >> eGuilde sarl - CTO > >> > > > > > > > > -- > > Denis Gervalle > > SOFTEC sa - CEO > > eGuilde sarl - CTO > > > > > > -- > Denis Gervalle > SOFTEC sa - CEO > eGuilde sarl - CTO > _______________________________________________ > devs mailing list > [email protected] > http://lists.xwiki.org/mailman/listinfo/devs > -- Ludovic Dubost Founder and CEO Blog: http://blog.ludovic.org/ XWiki: http://www.xwiki.com Skype: ldubost GTalk: ldubost _______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
