Stan, Sounds like a very ambitious implementation. So, IIUIC, you even have indexing/query support against the the primary storage? Or is it separated store/retrieve for performance?
Looking forward to take a closer look, and definitely news-worthy if we can bring this to production quality level. On Tue, Apr 27, 2010 at 5:13 PM, Stanislav Muhametsin <[email protected]> wrote: > Quoting Rickard Öberg <[email protected]>: > >> Can you briefly outline how you did that? What is the strategy? >> >> One EntityStore I am considering is to simply have a key-value table >> approach, which would at least enable using an RDBMS as a store, with >> transactions and all that. That I think would be useful for those who can't >> go the NoSQL route. > > Yeah, using RDBMS as entitystore is relatively simple - but performing > queries in sensible manner is hard unless the database table structure > itself supports the structure of entities. Shortly put - the RDBMS indexing > creates a single table for each qualified-name that is possible to use when > using entities, and uses those tables when performing queries. > > My current apporach is the following: > 1. At startup of application, the RDBMS-indexing scans for all entity types, > and ALL value composite types that can be used with them. > 2. If a schema used in configuration exists, current implementation drops > it, along with any data in it. This is because I haven't had time to > implement algorithm, which would sync database structure with application > entity structure. Obviously, this is an important todo. > 3. A mapping-table for entity types, containing id and class name, is > created, and each entity composite type is inserted to it. > 4. A mapping-table for used classes, containing id and class name is > created, and each used value composite type and enum type is inserted to it. > 5. A table containing common information about entities is created. It has > primary key, entity type id (from (3)), entity identity, modified timestamp, > entity version, and application version as columns. > 6. For each QualifiedName in each entity and value type, except > Identity.identity, a table is created. Table has a name of pattern > qname_<number>, and application contains mapping between each qualified name > and table representing it. Obivously the database should contain this > mapping too, in order to implement algorithm mentioned in (2). The structure > of each table is different whether the qualified name represents a primitive > property, property of value composite, or a collection of primitive or value > composite. If a qualified name represents a collection, two additional > tables are created (to unwind possible nested collection structure). > > The queries are then processed in a similar manner as with RDF. The pattern > is that disjunctions are transformed into SQL union, conjunctions are SQL > intersections, and the rest (or most of it) are normal SQL conditions in > WHERE-clause inside appropriate subquery. The transformation is a bit > complex, and might produce big queries for complex Qi4j-queries, especially > if there is an order by -statement, but the idea would seem to work on > conceptual level. I have no idea yet as if how quick (read: slow) it will > be. But SQL is pretty good when optimizing things, so even if it is > ultra-slow at start, by creating appropriate indexes, it is possible to > speed up things significally, so I am optimistic in that. > >> If anyone wants to pick that up, please let us know. >> > > I will have time for this in June at soonest, if no one else wants to do > this. > > > _______________________________________________ > qi4j-dev mailing list > [email protected] > http://lists.ops4j.org/mailman/listinfo/qi4j-dev > -- Niclas Hedhman, Software Developer http://www.qi4j.org - New Energy for Java I live here; http://tinyurl.com/2qq9er I work here; http://tinyurl.com/2ymelc I relax here; http://tinyurl.com/2cgsug _______________________________________________ qi4j-dev mailing list [email protected] http://lists.ops4j.org/mailman/listinfo/qi4j-dev
