Is not same as "Combined Disk and In-Memory Operation" (http://hsqldb.sourceforge.net/web/hsqlModes.html)???
Edson ----- Original Message ----- From: Brian McCallister To: OJB Users List Sent: Monday, September 15, 2003 5:10 PM Subject: Re: Prevayler based PB implementation Prevayler is a completely different idea from a relational database. HSQL in-memory is great for a lot of things (persistence not being one of them). Prevayler basically acts as a heap that survives restarts. -Brian On Monday, September 15, 2003, at 03:58 PM, Edson Carlos Ericksson Richter wrote: > Excuse me, but what is wrong with HSQL (or the derivative that is > configured to work in-memory? > Why can't we devote some time to improve HSQL, if it's not so > performatic as we want? > > > Edson > ----- Original Message ----- > From: Thomas Mahler > To: OJB Users List > Sent: Monday, September 15, 2003 4:41 PM > Subject: Re: Prevayler based PB implementation > > > Hi Olli, > > [EMAIL PROTECTED] wrote: >> Hej Thomas, >> >> >>> -----Original Message----- >> >> >>> during the weekend I wrote a new PB implementation that is based on >>> prevayler (http://sourceforge.net/projects/prevayler/). >> >> >> don't you have any hobbies? :-) > > I always thought coding is a well respected hobby in our meritocracy > ? :-) > >> >>> - A query engine must be implemented. This is the largest >>> todo. We need a >>> query engine, that is able to perform PB queries against the >>> in-memory >>> database. >> >> >> I wonder how this engine would look like. > > I'm also thinking about this and have not yet a clear picture. > >> Should it be done via a mapping to SQL? Then it is not our >> job but rather an issue for the prevayler project. Of course, >> the SQL must refer to a virtual O/R-mapping then. > > I don't think that the Prevayler team would regard this as within > their > scope. They care about persisting your business models. But they do > not > care about querying at all. > It's the users responsibility to navigate and search accross the > business model. > > SO if we want to have a SQL engine we'll have to find one or to > develop > it on our own. > > Doing it this way would allow to reuse the existing SqlGenerator and > it > would allow to use bot Criteria and SQL based queries. > > OTOH i think that it's a lot of work :-( > >> >> Or should it support the PB query API directly? > > That was my original idea. But there are some tricky issues to solve. > Only consider a query against class C with to criteria a and b that > are > linked by AND. > How to avoid > 1. a full scan of all C instances to build a collection of all > instances > matching a.? > 2. a full scan of all instances in this collection to filter all > instance also matching b? > >> What about those features in the API that refer to the >> Database schema directly (such as SQLQuery)? > > Sql based queries won't work in this Approach. That's a real > disatvantage of this approach. > >> >>> Any ideas for this are welcome. This engine could be reused >>> to provide >>> in-memory queries for ODMG and JDO. >> >> >> Sounds cool. However, I doubt that it would have essential >> impact. For prototyping and testing, HSQL is sufficiently convenient, >> and in real life, customers want RDBMS. That is my what I guess >> at least. > > I agree. For most enterprise application that I have seen RDBMS are > meant to stay. > > But I think there are other areas (for instance embedded > applications) > where some architects would prefer to not use a RDBMS. > For these areas a Minimum-footprint solution like OJB/Prevayler > could be > an ideal solution. > > Prevayler gained a lot of momentum even for web based applications. > But > after the first enthusiasm developers see that several things (like > transactions, standardized persistence APIs, and queries) are simply > not > present. > So I think there could be a niche market for a OJB/Prevayler OODBMS. > > (If I'm wrong it was at least fun to code... ) > > cheers, > Thomas > >> >> regards, >> Olli >> >> >> >> >> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: [EMAIL PROTECTED] >> For additional commands, e-mail: [EMAIL PROTECTED] >> >> > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > > > --- > Outgoing mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.518 / Virus Database: 316 - Release Date: 11/9/2003 --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.518 / Virus Database: 316 - Release Date: 11/9/2003 --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
